Diurnal evolution of total column and surface atmospheric ammonia in the megacity of Paris, France, during an intense springtime pollution episode
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Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Diurnal evolution of total column and surface atmospheric ammonia in the megacity of Paris, France, during an intense springtime pollution episode Rebecca D. Kutzner1 , Juan Cuesta1 , Pascale Chelin1 , Jean-Eudes Petit2,3 , Mokhtar Ray1 , Xavier Landsheere1 , Benoît Tournadre1,a , Jean-Charles Dupont4 , Amandine Rosso5 , Frank Hase6 , Johannes Orphal6 , and Matthias Beekmann1 1 Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS 7583, Université Paris-Est Créteil, Université de Paris, Institut Pierre-Simon Laplace (IPSL), Créteil, France 2 Laboratoire des Sciences du Climat et de l’Environnement, UMR 8212, CEA/Orme des Merisiers, 91191 Gif-sur-Yvette, France 3 INERIS, Parc Technologique ALATA, 60750 Verneuil-en-Halatte, France 4 Institut Pierre-Simon Laplace, École Polytechnique, UVSQ, Université Paris-Saclay, 91128 Palaiseau, France 5 Airparif, Agence de surveillance de la qualité de l’air, Paris, France 6 Institut für Meteorologie und Klimaforschung (IMK), Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany a new affiliation: Centre Observation, Impacts, Energy – Mines ParisTech, Sophia Antipolis CEDEX, France Correspondence: Rebecca D. Kutzner (rebecca.kutzner@lisa.u-pec.fr) and Pascale Chelin (pascale.chelin@lisa.u-pec.fr) Received: 27 July 2020 – Discussion started: 8 December 2020 Revised: 8 July 2021 – Accepted: 9 July 2021 – Published: 12 August 2021 Abstract. Ammonia (NH3 ) is a key precursor for the for- servatory at an urban site over the southeastern suburbs of the mation of atmospheric secondary inorganic particles, such Paris megacity. This analysis considers the following mete- as ammonium nitrate and sulfate. Although the chemical orological variables and processes relevant to the ammonia processes associated with the gas-to-particle conversion are pollution event: temperature, relative humidity, wind speed well known, atmospheric concentrations of gaseous ammo- and direction, and the atmospheric boundary layer height (as nia are still scarcely characterized. However, this informa- indicator of vertical dilution during its diurnal development). tion is critical, especially for processes concerning the equi- Moreover, we study the partitioning between ammonia and librium between ammonia and ammonium nitrate, due to ammonium particles from concomitant measurements of to- the semivolatile character of the latter. This study presents tal particulate matter (PM) and ammonium (NH+ 4 ) concen- an analysis of the diurnal cycle of atmospheric ammonia trations at the surface. We identify the origin of the pollu- during a pollution event over the Paris megacity region in tion event as local emissions at the beginning of the analyzed spring 2012 (5 d in late March 2012). Our objective is to an- period and advection of pollution from Benelux and west- alyze the link between the diurnal evolution of surface NH3 ern Germany by the end. Our results show a clearly different concentrations and its integrated column abundance, mete- diurnal behavior of atmospheric ammonia concentrations at orological variables and relevant chemical species involved the surface and those vertically integrated over the total at- in gas–particle partitioning. For this, we implement an orig- mospheric column. Surface concentrations remain relatively inal approach based on the combined use of surface and to- stable during the day, while total column abundances show tal column ammonia measurements. These last ones are de- a minimum value in the morning and rise steadily to reach rived from ground-based remote sensing measurements per- a relative maximum in the late afternoon during each day formed by the Observations of the Atmosphere by Solar In- of the spring pollution event. These differences are mainly frared Spectroscopy (OASIS) Fourier transform infrared ob- explained by vertical mixing within the boundary layer, pro- Published by Copernicus Publications on behalf of the European Geosciences Union.
12092 R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris
vided that this last one is considered well mixed and there- in soils, plants and the soil–plant interaction, as described in
fore homogeneous in ammonia concentrations. This is sug- detail by Behera et al. (2013). At the global scale, ammo-
gested by ground-based measurements of vertical profiles nia emissions are mainly attributed to agriculture, biomass
of aerosol backscatter, used as tracer of the vertical distri- burning and the energy sector, accounting in 2005 for 80.6 %,
bution of pollutants in the atmospheric boundary layer. In- 11.0 % and 8.3 %, respectively (Behera et al., 2013).
deed, the afternoon enhancement of ammonia clearly seen by The European Union (EU) addressed ammonia
OASIS for the whole atmospheric column is barely depicted emission in the National Emission Ceilings Direc-
by surface concentrations, as the surface concentrations are tive 2001/81/EC (NECD). Serrano et al. (2019) recently
strongly affected by vertical dilution within the rising bound- reviewed reduction efforts of nitrogen levels between 2001
ary layer. Moreover, the concomitant occurrence of a de- and 2011, finding a significant impact of ammonia emitted
crease in ammonium particle concentrations and an increase from agriculture on ecosystems. Exceedances of ammonia
in gaseous ammonia abundance suggests the volatilization of emissions compared to ceilings set for 2010 are still occur-
particles for forming ammonia. Furthermore, surface obser- ring (NECD reporting status 2018). New reduction goals for
vations may also suggest nighttime formation of ammonium the period of 2020 to 2029 and a second period after 2030 are
particles from gas-to-particle conversion, for relative humid- set for each European country in Directive (EU) 2016/2284.
ity levels higher than the deliquescence point of ammonium Pollution events in urban areas directly impact human
nitrate. health and greatly reduce visibility (e.g., Molina and Molina,
2004). This recurrently occurs during springtime over the
Paris megacity (12.2 million inhabitants including suburbs)
and other European megacities often associated with emis-
1 Introduction sions from agricultural activities in the areas surrounding
the agglomerations (e.g., Petit et al., 2015). Other pollution
Ammonia (NH3 ) is a harmful air pollutant that directly af- events in these areas are also linked to local or regional emis-
fects human health and also contributes to intense smog sions of nitrogen oxides and sulfur dioxide from road traf-
events through the neutralization of sulfuric and nitric acids fic and industry (Behera and Sharma, 2010). Accurate and
for forming secondary aerosols such as ammonium sulfate long-term measurements of atmospheric pollutants, such as
((NH4 )2 SO4 ) and nitrate (NH4 NO3 ) (Behera et al., 2013; ammonia, and meteorological conditions are crucial in order
Seinfeld and Pandis, 2016; Elster et al., 2018). These par- to better understand the origin and the evolution of these pol-
ticles can be transported over long distances, contribute to lution events. In the Paris region, springtime is a very pro-
the degradation of air quality and impact different ecosys- pitious period for particulate matter pollution episodes, es-
tems. Through conversion into different forms of reactive ni- sentially dominated by secondary inorganic aerosols, such
trogen, further impacts of ammonia and ammonium particles as ammonium nitrate and sulfate (Sciare et al., 2011; Petit
are directly or indirectly linked to acidic precipitation, acidi- et al., 2015). Concomitantly, ammonia concentrations have
fication, eutrophication and loss of biodiversity (e.g., Sutton been found to be exceptionally high, as reported by surface
et al., 2011, 2013; Krupa, 2003). Depending on atmospheric in situ measurements (Petit et al., 2015; Petetin et al., 2016)
temperature (T ), relative humidity (RH) and the pH of the and remote sensing from the ground and satellite (Tournadre
particles, volatilization of ammonium nitrate particles may et al., 2020; Viatte et al., 2020). Indeed, that period of the
form gaseous ammonia (e.g., Seinfeld and Pandis, 2016; We- year is characterized by fertilizer spreading, which can dra-
ber et al., 2016; Guo et al., 2018). matically enhance NH3 emissions (Ramanantenasoa et al.,
The main source of NH3 in Europe is the agricultural sec- 2018).
tor, with an average of 93 % of total ammonia emission es- Different techniques are used to measure concentrations
timated for 2018 (Pinterits et al., 2020). It is emitted by of NH3 in the atmosphere. Difficulties to measure ammonia
volatilization from fertilizer storage, livestock, and manure by in situ techniques are associated with its “sticky” nature,
and mineral nitrogen fertilizers applied to crops as a function inducing its accumulation in inlets and sampling tubes. In
of temperature, humidity, and pH of atmosphere and soil as order to reduce these artifacts, different techniques are often
well as wind speed (e.g., Sommer et al., 2004, Behera et al., implemented, such as the use of polyethylene or Teflon tubes
2013). Other emissions are associated with traffic and indus- (instead of steel or silicosteel) and halocarbon wax coating,
try. In France, the dominant source of NH3 is also attributed while keeping the length of the tubes to a minimum possible
to the agricultural sector, with contributions between 94 % and a heating system for reducing relative humidity that may
and 98 %, among which 50 % is due to nitrogen-based fer- also lead to losses of NH3 (Yokelson et al., 2003; Whitehead
tilizers as well as emissions from livestock (Génermont et et al., 2008).
al., 2018; Ramanantenasoa et al., 2018). In many regions of Remote sensing of ammonia is an innovative alternative
Africa, Inner Mongolia, southern Siberia and South America, to in situ techniques, which offers a significant enhance-
fires are another anthropogenic source of NH3 (Behera et al., ment of spatial coverage. Satellite approaches are currently
2013). Natural sources are related to biological mechanisms based on hyperspectral thermal infrared measurements from
Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021
R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris 12093
the Cross-track Infrared Sounder (CrIS; Shephard and Cady- also provide a brief description of the new retrieval of am-
Pereira, 2015) and the infrared atmospheric sounding inter- monia from OASIS (Tournadre et al., 2020). In the third sec-
ferometer (IASI; Clerbaux et al., 2009), respectively, aboard tion, we present and discuss the analysis of these datasets.
the United States Suomi National Polar-orbiting Partner- First, we describe the regional conditions of the Paris pollu-
ship (SNPP) and the European MetOp (Meteorological Oper- tion event in late March 2012 using meteorological analysis,
ational) satellites. Both platforms are pointing nadir in polar a chemistry–transport model and satellite data (Sect. 3.1).
sun-synchronous orbits, with overpasses around 09:30 and Then, we analyze the diurnal evolution of surface and total
21:30 LT (local time) for IASI and 13:30 and 01:30 LT for columns of ammonia and particulate matter as well as mete-
CrIS (Shephard and Cady-Pereira, 2015; Dammers et al., orological variables over the Paris region (Sect. 3.2 to 3.4).
2017). Therefore, they both offer global coverage twice a Following that, we analyze the complementarity of surface
day, providing particularly valuables measurements over re- and total column measurements of ammonia using ground-
mote regions lacking ground-based instruments such as in based backscatter lidar (LIght Detection And Ranging) mea-
the tropics. Remote sensing of ammonia can also be per- surements, as a proxy for the vertical distribution of pollu-
formed using hyperspectral measurements from a ground- tants within the atmospheric boundary layer (Sect. 3.5). Sec-
based Fourier transform infrared (FTIR) spectrometer, like tion 4 provides conclusions of this study.
OASIS (Observations of the Atmosphere by Solar Infrared
Spectroscopy; Chelin et al., 2014) mid-resolution obser-
vatory in Créteil (France). Remote sensing from satellite 2 Datasets
and ground-based platforms provides vertically integrated
2.1 Description of ground-based sites and platforms
amounts of ammonia over the atmospheric column for cloud-
free conditions. The combined use of remote sensing and in An original aspect of this work is the analysis of the diurnal
situ measurements offers an interesting framework for ana- evolution of total column observations of ammonia derived
lyzing ammonia variability both at the surface and integrated from OASIS. This remote sensing observatory is located
over the atmospheric column, as already done for greenhouse in Créteil (OASIS; 48.79◦ N, 2.44◦ E; 56 m a.s.l., above sea
gases (Zhou et al., 2018). FTIR ground-based measurements level), in the southeastern suburbs of Paris, on the rooftop of
can provide highly valuable information on the diurnal evo- the Université Paris-Est Créteil (UPEC; Chelin et al., 2014).
lution of atmospheric species for a particular geographical It is an urban site mainly affected by background levels of
location, as shown here for ammonia in the Paris suburbs. Al- pollution (Fig. 1).
though numerous FTIR ground-based stations currently ex- Measurements from other sites over the Paris region are
ist, such as those of the Network for the Detection of Atmo- also used in the current study (Fig. 1). Meteorological and
spheric Composition Change (NDACC; De Mazière et al., detailed atmospheric composition data at the surface level are
2018), only a few of them document the diurnal evolution of measured at the “Site Instrumental de Recherche par Télédé-
atmospheric constituents. tection Atmosphérique” supersite near Palaiseau (SIRTA;
This paper presents a detailed analysis of the diurnal evo- 48.72◦ N, 2.20◦ E; http://sirta.ipsl.fr, last access: 29 Jan-
lution of ammonia as observed in total columns from ground- uary 2019), located about 19 km southwest from OASIS and
based remote sensing and at the surface from an in situ ana- southwest of Paris, which is often used for monitoring back-
lyzer in Paris, France, during a major pollution event in late ground air quality conditions in the Paris region (Haeffelin et
March 2012. We characterize the diurnal variation of ammo- al., 2005). We use radiosounding measurements of temper-
nia, analyzing both the link with the formation and volatiliza- ature, pressure and humidity profiles from the Trappes sta-
tion of ammonium particles and vertical dilution in the at- tion that is about 31 km west of Créteil (15 km away from
mospheric boundary layer. Spring 2012 was one of the most the SIRTA supersite) and operated by Météo-France. Addi-
polluted periods since 2007, with a succession of persistent tional surface measurements of PM2.5 and PM10 (particle
pollution events (Petit et al., 2015, 2017). We use total col- matter with aerodynamic diameters, respectively, less than
umn ammonia concentrations derived from the OASIS obser- 2.5 and 10 µm) are provided by the Airparif network ded-
vatory in the southeastern Paris suburbs (Créteil) and surface icated to monitoring air quality in the Paris region (https:
observations in the southwestern Paris suburbs (Palaiseau) //www.airparif.asso.fr/, last access: 17 January 2019) from
to characterize the diurnal evolution of ammonia between the stations of Vitry-sur-Seine, Bobigny and Gennevilliers. In
26 and 30 March 2012. To the authors’ knowledge, this is the paper, time series of measurements are presented in terms
the first analysis of the diurnal evolution of ammonia from of hourly median values, except when stated otherwise.
both total column and surface measurements, in close rela-
tion with particle-phase measurements.
Section 2 provides information concerning the instruments
from the OASIS and SIRTA (Site Instrumental de Recherche
par Télédétection Atmosphérique) sites, as well as other
datasets (see Sect. 2.1, 2.4 and 2.5) used for this study. We
https://doi.org/10.5194/acp-21-12091-2021 Atmos. Chem. Phys., 21, 12091–12111, 2021
12094 R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris
Figure 1. Outline of the Paris region and a zoomed-in view of the relevant sites (A – Airport Orly, B – Bobigny, G – Gennevilliers, O – OASIS,
P – Palaiseau, S – SIRTA, T – Trappes, VsS – Vitry-sur-Seine) using shapefiles provided by data.gouv.fr (https://www.data.gouv.fr/fr/datasets/
espaces-agricoles-de-la-region-ile-de-france-inscrits-sur-la-cdgt-du-sdrif-arrete-en-2012-idf/#discussion-5cc30bdb8b4c4166219c058e,
last access: 30 April 2019) and processed with QGIS 3.6.
2.2 Observations of total column ammonia derived lar position. The altitude–azimutal solar tracker of OASIS
from OASIS uses bare gold-coated mirrors (A547N model from Bruker
Optics). Infrared solar radiation spectra are recorded by a
DTGS (deuterated triglycine sulfate) detector using a potas-
Since 2009, the OASIS observatory regularly records high
sium bromide (KBr) beam splitter to cover the large spec-
spectral measurements of solar radiation absorbed and scat-
tral region from 700 to 11 000 cm−1 (0.9–14.3 µm) with no
tered by atmospheric constituents, under clear-sky conditions
optical filter. The acquisition system is set to average over
(Chelin et al., 2014). It uses a medium-spectral-resolution
30 scans at maximum spectral resolution in order to increase
Fourier transform spectrometer manufactured by Bruker Op-
the signal-to-noise ratio of the measurements. This averag-
tics (the Vertex 80 model) with a spectral resolution of
ing procedure results in an effective temporal resolution of
0.06 cm−1 (corresponding to a maximum optical path dif-
10 min, that allows for measuring the diurnal variability of
ference of 12 cm). OASIS is routinely used for monitoring
relatively short-lifetime species such as NH3 . Absolute cali-
air pollutants, such as tropospheric ozone (O3 ) and carbon
bration of spectra measured by OASIS is done every month
monoxide (CO), with good accuracy and high sensitivity to
with a reference internal source of radiation.
near-surface concentrations (Viatte et al., 2011). This system
Ammonia concentrations integrated over the total atmo-
is particularly suited for air quality monitoring in megacities,
spheric column are retrieved with the PROFFIT 9.6 code
given its compactness and moderate cost, and it can play a
developed by the Karlsruhe Institute of Technology (Ger-
key role in validating current (e.g., IASI) and future satel-
many; Hase et al., 2004), adapted for the medium spectral
lite observations (e.g., Infrared Atmospheric Sounder Inter-
resolution. As detailed by Tournadre et al. (2020), two spec-
ferometer Next Generation – IASI-NG – and the infrared
tral microwindows within the ν2 vibrational band of NH3 are
sounder aboard the Meteosat Third Generation mission –
used: 926.3–933.9 and 962.5–970 cm−1 . The main interfer-
MTG/IRS).
ing species in this spectral range are water vapor (H2 O), car-
The observatory is covered by an automatized cupola (Sir-
bon dioxide and O3 , whose abundances are taken from the
ius 3.5 “School Model” observatory, 3.25 m high and 3.5 m
Whole Atmosphere Community Climate Model (WACCM
in diameter), in which the aperture rotates to track the so-
Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021
R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris 12095
2.3 Surface in situ observations of ammonia and
aerosol composition
In the present analysis, we use in situ gaseous ammonia mea-
surements at surface level carried out with an AiRRmonia in-
strument (Mechatronics Instruments, the Netherlands) at the
SIRTA observatory (Haeffelin et al., 2005). The principle of
this instrument, described in Cowen et al. (2004), is essen-
tially based on conductimetric detection of ammonia that is
first absorbed via a gas-permeable membrane and dissolved
in water (i.e., in the form of ammonium ions, forming acidic
solution). Several intercomparison exercises have shown that
this procedure provides more accurate NH3 measurements
(Norman et al., 2009; von Bobrutzki et al., 2010). The AiR-
Figure 2. OASIS FTIR atmospheric spectrum recorded with the
Rmonia was regularly calibrated with 0 and 500 ppb ammo-
Bruker Vertex 80 at Créteil on 21 March 2012 in the two microwin-
nium solution.
dows (before and after the spectral gap), showing the strong am-
monia absorbing lines (pointed out by the green arrows) around Concomitant measurements of the major chemical compo-
932 cm−1 (origin of the NH3 ν2 band) with individual contribu- sition of submicron aerosols were performed with an aerosol
tions of the main interfering species represented from the atlas of chemical speciation monitor (ACSM; Aerodyne Research
Meier et al. (2004). All spectra are plotted using arbitrary unit (a.u.) Inc., Billerica, MA, USA; Ng et al., 2011), providing concen-
on the y axis. trations of particulate organic matter (OM), nitrate (NO− 3 ),
2− + −
sulfate (SO4 ), ammonium (NH4 ) and chloride (Cl ), ev-
ery 30 min. Submicron particles are sampled at 3 L min−1 ,
version 6: Chang et al., 2008) and jointly adjusted with that subsampled at 0.85 L min−1 and focused through an aerody-
of NH3 . We also use climatological concentrations for mi- namic lens for PM1 (particle matter with aerodynamic di-
nor interfering gases (i.e., nitric acid, HNO3 ; sulfur hexaflu- ameter smaller than 1 µm). Non-refractory particles are then
oride, SF6 ; ethane, C2 H4 ; and chlorofluorocarbons – e.g., flash-vaporized on a 600 ◦ C heated plate, fragmented by elec-
CFC-12) that may essentially impact the baseline of the spec- tronic impact at 70 keV, and eventually separated and de-
tra. The spectral signatures of absorption of infrared radiation tected by a quadrupole. Calibrations were performed by in-
by ammonia are clearly seen in individual spectra measured jecting known concentrations of ammonium nitrate and am-
by OASIS, such as those recorded during a pollution event monium sulfate particles with an aerodynamic diameter of
in March 2012 (as compared to the atlas from Meier et al., 300 nm. Details on the operational conditions of the AiR-
2004; see Fig. 2). Atmospheric columns of ammonia derived Rmonia and the ACSM instruments at SIRTA are provided
from the 9-year database of OASIS range from 0.0005 × by Petit et al. (2015).
1016 to 9×1016 molec. cm−2 (molecules per square centime- As observed by Petit et al. (2015), we expect the daily evo-
ter), and their retrieval error is estimated to be 20 %–35 % lution of ammonia over the Paris region to be closely linked
(Tournadre et al., 2020), dominated by the systematic errors to the gas-to-particle conversion between ammonia (gas) and
that are the combination of uncertainties in the spectroscopic ammonium nitrate particles. This is a reversible conversion
parameters of ammonia and the interfering species (the domi- for which the equilibrium is closely linked to the abundance
nating term), radiometric noise, instrumental parameters, and of precursors (NH3 and HNO3 ) and meteorological condi-
forward model uncertainties. The magnitudes of these errors tions, such as temperature and relative humidity (Seinfeld
are comparable to those estimated by Dammers et al. (2015) and Pandis, 2016). The conditions needed for volatilization
for a high-resolution ground-based station at Bremen (Ger- of NH3 from NH4 NO3 are given by the relationship of rel-
many). OASIS retrievals of NH3 total columns show a good ative humidity and deliquescence relative humidity (DRH),
agreement with co-located observations derived from IASI which depends on temperature, whereby volatilization is fa-
(the ANNI-NH3-v2.2R version; Van Damme et al., 2017): a vored when RH is much lower than DRH. In order to estimate
linear correlation coefficient of ∼ 0.8 and a small mean dif- the balance between DRH and RH, we consider the follow-
ference of ∼ 0.08 × 1016 molec. cm−2 , with OASIS-derived ing equation, as suggested by Seinfeld and Pandis (2016):
concentrations slightly larger (Tournadre et al., 2020). This
last aspect could be associated with an enhanced sensitivity 1HS 1 1
to larger concentrations of NH3 near the surface for OASIS DRH(T ) = DRH(298) exp A −
R T 298
as compared to the satellite retrieval which is most sensitive
T
to higher atmospheric layers. −B ln − C(T − 298) , (1)
298
https://doi.org/10.5194/acp-21-12091-2021 Atmos. Chem. Phys., 21, 12091–12111, 2021
12096 R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris
where DRH(298) is the deliquescence relative humidity of that are inserted in the CHIMERE model for calculating the
NH4 NO3 at 298 K, which corresponds to 61.8 %. 1HS is thermodynamic equilibrium of the species. Ammonia, nitrate
the enthalpy of solution for NH4 NO3 at 298 K which is and sulfate are simulated in aqueous, gaseous and particulate
25.69 kJ mol−1 , R is the universal gas constant and T is the phases in the model.
temperature in kelvin. A, B and C are factors for the solu- Meteorological conditions are analyzed from in situ mea-
bility of common aerosol salts in water as a function of tem- surements and numerical model simulations. We use sea-
perature provided by Seinfeld and Pandis (2016) (i.e., 4.3, level pressure, wind and potential temperature fields from
−3.6 × 10−2 and 7.9 × 10−5 , respectively). Moreover, parti- the ERA-Interim (ERAI; Simmons et al., 2007) reanalysis
tioning between ammonia and ammonium nitrate is also in- of the European Centre for Medium-Range Weather Fore-
fluenced by the pH of the ambient particles (e.g., Weber et casts (ECMWF) that are provided by the Institut Pierre-
al., 2016; Guo et al., 2018). When pH drops below an ap- Simon Laplace Mésocentre (https://mesocentre.ipsl.fr, last
proximate critical value of 3 (slightly higher in warm and access: 6 March 2019). These simulations have a 0.75×0.75◦
slightly lower in cold seasons), the NH3 reduction leads to horizontal resolution and 37 pressure levels.
evaporation of NH4 NO3 , while this is not expected to hap-
pen for moderately acidic to neutral conditions (Guo et al., 2.5 Local conditions in the Paris region from
2018). In addition, it is worth noting that in the present study ground-based measurements
we use the above expression and the currently available data
for a qualitative interpretation of diurnal variations of am- Meteorological conditions at the surface over the Paris region
monia and ammonium. However, additional dedicated mea- are analyzed by in situ measurements of wind speed and di-
surements throughout the atmospheric column are needed in rection performed at the SIRTA site (Haeffelin et al., 2005).
order to perform a quantitative analysis (see more details in Local temperature and relative humidity were measured at
the conclusion section). Créteil with a LOG 110-EXF sensor, with an accuracy in
temperature of ±0.5 ◦ C and in relative humidity of ±3 %.
2.4 Regional conditions from satellite data and models Vertical profiles of temperature and relative humidity from
the surface up to 25 km of altitude and with about 10 m ver-
For characterizing the pollution event during March 2012, tical resolution are measured by radiosoundings launched
we use a suite of satellite and model datasets concern- around noon and midnight at the Trappes site (southwest sub-
ing both the pollutant distributions at regional and conti- urbs of Paris).
nental scales and meteorological conditions. Aerosol opti- The diurnal evolution of particle pollution over the Paris
cal depth (AOD) data derived from satellite and ground- region is studied in terms of surface measurements of PM2.5
based measurements are used for analyzing the spatial and and PM10 from several Airparif sites and AOD measured
temporal evolution of total particle abundance integrated by ground-based sun photometers (version 3 of level 2.0
over the atmospheric column. The horizontal distribution data) at the Paris and SIRTA sites from AERONET (AErosol
of AOD over western Europe is described using MODIS RObotic NETwork; Holben et al., 2001, https://aeronet.gsfc.
(Moderate Resolution Imaging Spectroradiometer; Remer et nasa.gov/, last access: 9 June 2019). We use the distinction
al., 2005) data aboard the Terra (MOD04L2) satellite with between AOD from a fine (e.g., smoke or smog) and coarse
overpasses at 10:30 LT (from the NASA Worldview website (e.g., sea-salt or dust) modes at 500 nm, derived from the
https://worldview.earthdata.nasa.gov/, last access; 27 Febru- wavelength dependence of the AOD (O’Neill et al., 2003;
ary 2019; Levy and Hsu, 2015). The MODIS images have a Giles et al., 2019). Errors in AOD data correspond to approx-
horizontal resolution of 3 km at nadir. imately 0.02 (Giles et al., 2019).
The horizontal distribution of air pollutants at the Euro- Additionally, we use ground-based lidar measurements
pean scale is studied with CHIMERE chemistry–transport from the SIRTA site for describing the vertical distribution
model simulations of PM2.5 provided by the ESMERALDA of particles over the Paris region, which is used as an in-
(EtudeS Multi RégionALes De l’Atmosphère; Cortinovis dicator of the vertical distribution of air pollutants and the
et al., 2006) project (http://www.esmeralda-web.fr/accueil/ vertical structure of the atmospheric boundary layer. This is
index.php, last access: 28 February 2019). The version 2008b done with vertical profiles of attenuated backscatter profiles,
of CHIMERE is run hourly and averaged at a daily timescale, measured by an elastic backscatter lidar (the Leosphere ALS
with a horizontal resolution of 15 km × 15 km and nine ver- model) at 355 nm. The mixing boundary layer height is visu-
tical levels between 20 m to 5 km. Meteorological inputs for ally identified as the lowest marked discontinuity of the lidar
CHIMERE come from MM5 simulations (Dudhia, 1993), profiles during daytime hours (from 06:00 to 18:00 UTC).
using Final (FNL) analysis data from National Centers for
Environmental Prediction (NCEP) as boundary conditions.
Chemical reactions are simulated using the MELCHIOR2
mechanisms scheme and the ISORROPIA model (Nenes et
al., 1998). This last one has been used to produce tables
Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021
R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris 12097
3 Results polluted air masses are advected from Benelux and west-
ern Germany during 28–29 March, PM2.5 levels are clearly
We focus our study on the diurnal evolution of ammonia dur- enhanced (up to 80 µg m−3 ), as also seen in daily averaged
ing a major pollution event over the Paris region occurring simulations. Figure 4 also shows the largest peaks of surface
at the end of March 2012. It corresponds to the period with PM2.5 concentrations occurring every day during the morn-
highest concentrations of ammonia on the multiyear time se- ing and secondary high values in the late evening.
ries (2009–2017) of OASIS measurements, which is proba- Very similar temporal evolution patterns of surface particle
bly linked to the springtime spreading of mineral fertilizer concentrations are observed over the whole Paris region and
in the Paris region and the surrounding regions (Ramanan- during the entire period (26–30 March), both in absolute and
tenasoa et al., 2018; Tournadre et al., 2020). It is the most relative terms. Figure 4 illustrates this horizontally homoge-
polluted spring season between 2007 and 2015 (Petit et al., neous distribution of surface PM as the chosen stations are
2017). located at the southeastern, southwestern, northeastern and
northwestern suburbs of Paris (Fig. 1). The same peaks and
3.1 Meteorological and atmospheric conditions over troughs of surface PM are seen for all these locations. Par-
western Europe ticularly, we also remark that PM1 at SIRTA also shows the
same temporal evolution as other stations in the Paris region
During late March 2012, the prevailing atmospheric condi- but with levels roughly ∼ 30 % below those of PM2.5 dur-
tions over western Europe are driven by an anticyclonic high- ing 26–28 March and similar concentrations afterwards (for
pressure system centered over Great Britain and the North both PM1 and PM2.5 ). The 30 % difference between PM1 and
Sea (55◦ N, 0◦ E) on 26 March and moving westwards in the PM2.5 observed in the present case could be linked with ag-
following days (see Fig. 3a, d and g). Following the anticy- ing (and/or long-range transport) which has been remarked
clonic circulation associated with this system, northeasterly for measurements in 2015 by Petit et al. (2017). In the Paris
winds blow from the Benelux region (Belgium, the Nether- region, PM1 generally represents 90 % of PM2.5 (Petit et al.,
lands and Luxembourg) to northern France. As expected for 2017), particularly when PM1 is larger than 20 µg m−3 (al-
an anticyclonic period, relatively low wind speeds occur at though for lower levels, PM1 may represent around 50 % of
its core, located over central Europe (from southern France PM2.5 ; Petit, 2014). Occasionally, some background levels
to eastern Germany), which are accompanied by high insula- of PM might not be accounted for in PM1 that are measured
tion and low cloudiness (not shown). According to MODIS as PM2.5 (Petit, 2014). Moreover, comparisons made by Pe-
satellite observations (Fig. 3b, e and h) and CHIMERE sim- tit (2014) show a very similar statistical distribution for both
ulations (Fig. 3c, f and i), an aerosol plume with moder- PM1 at SIRTA and PM2.5 at the urban background stations
ate AOD (0.2 to 0.3) and moderately large concentrations in Paris suburbs mentioned in Fig. 4. For the future, it should
of PM2.5 at the surface (20 to 30 µg m−3 ) is formed on be very interesting to have co-located PM1 and PM2.5 chem-
26 March over Benelux and extends across the English Chan- ical composition measurements. The clear similarity of these
nel. Meanwhile, aerosol baseline levels are observed over measurements at four different locations of the Paris sub-
northern France (AOD ∼ 0.1 and 10–15 µg m−3 for surface urbs suggests that we may also expect a consistent evolution
PM2.5 ). After 27 March, the aerosol plume reaches north- of pollution levels at the Créteil site (OASIS observatory),
ern France and southern England. On 28 March, a clear en- whose observations are also used later in this section for ana-
hancement of the aerosol load over Benelux and northern lyzing the evolution of the atmospheric ammonia concentra-
France is observed both in terms of AOD (up to 0.4) and tions during the event.
modeled surface PM2.5 concentrations (up to 50 µg m−3 ). The time series of surface PM levels suggest the occur-
These high aerosol loads over northern France remain un- rence of two distinct pollution regimes within the period of
til 30 March (not shown). Both the horizontal extent of the 26–30 March. Indeed, while daily mean PM2.5 values dur-
aerosol plume and wind directions suggest that these highly ing 26–27 March remain under the air quality 24 h guideline
polluted air masses originate over Benelux as well as western of WHO (World Health Organization, PM2.5 of 25 µg m−3 ,
Germany and are transported southwestwards, clearly reach- except for one station on 1 single day), this PM2.5 threshold
ing the Paris region after 28 March (also remarked for this is exceeded for all stations during 28–30 March. Hereafter,
pollution event by Fortems-Cheiney et al., 2016). these two regimes are named period 1 or P1 (26–27 March)
and period 2 or P2 (28–30 March). These two different atmo-
3.2 Geographical distribution of particle matter over spheric conditions are also pointed out by Petit et al. (2015)
the Paris region by analyzing this particular pollution episode using surface
measurements at SIRTA. A statistical comparison of the sim-
Over the Paris region, particle concentrations at the surface ilarity of surface PM measurements from different sites over
are moderately high during 26–27 March (PM2.5 concentra- the Paris region is shown in Table 1 (for periods 1 and 2).
tions up to 40 µg m−3 ; see surface measurements of PM lev- For the first period (26–27 March), the time series of hourly
els from several stations of the Paris region in Fig. 4). As PM2.5 measurements performed at three different locations
https://doi.org/10.5194/acp-21-12091-2021 Atmos. Chem. Phys., 21, 12091–12111, 202112098 R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris
Figure 3. (a, d, g) Meteorological conditions characterized by 950 hPa winds (arrows) and sea level pressure (shading) over Europe (15◦ W
to 20◦ E and 40 to 65◦ N) from ERAI reanalysis in 26–28 March 2012. Horizontal distribution of particles over northern France (−5 to 7◦ E
and 45 to 52.5◦ N) in terms of (b, e, h) AOD at 550 nm from MODIS aboard the Terra satellite and (c, f, i) surface PM2.5 (in µg m−3 ) from
the CHIMERE model during the period 26–28 March 2012.
show a moderate correlation between each other (R 2 of 0.63 3.3 Evolution of ammonia concentrations over the
to 0.67), suggesting a similar evolution but with some hori- Paris region
zontal heterogeneity over the Paris region. During the second
period (28–30 March), correlations between PM measure- During the P1 and P2, ammonia concentrations over the
ments are clearly higher (R 2 of 0.86 to 0.91) and therefore Paris region are observed both at surface level (using in
indicate a more horizontally homogeneous PM distribution situ analyzer at SIRTA) and integrated over the total at-
over the Paris region. Levels of surface PM10 for the same mospheric column (using OASIS at Créteil, Fig. 5). To-
stations and periods show similar behaviors (Table 1). This tal atmospheric columns of NH3 show a very marked and
different behavior between P1 and P2 is likely linked to the clear diurnal evolution: lower column amounts of ammo-
origin of the pollution event, being rather local for P1 and nia in the morning that rise almost monotonically during
dominant advection of air pollution from Benelux during P2, the day until reaching a maximum in the afternoon. Both on
as remarked in the regional analysis of AOD, PM and wind 26 and 27 March, stable ammonia concentrations around 2 ×
regimes of Sect. 3.1. Additionally, we note that comparisons 1016 molec. cm−2 remain until noon and then increase only
of PM2.5 from three stations to PM1 at SIRTA show moderate in the afternoon. Early morning total columns of NH3 dur-
correlations during P1 as the other measurements but lower ing 28 and 29 March are lower (respectively, 1.4 × 1016 and
ones during P2 (although peaks and troughs are clearly coin- 0.6 × 1016 molec. cm−2 ) than for the previous days and show
cident). a steady enhancement from the early morning to the after-
noon. The highest total column of ammonia is measured
Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris 12099
Table 1. Correlation of different available PM values of Vitry, Gennevilliers, Bobigny and SIRTA sites during 26–27 March (period 1) and
28–30 March (period 2). SE refers to standard error, and R 2 refers to the square of the correlation coefficient.
26–27 March (period 1) 28–30 March (period 2)
Slope SE R2 Slope SE R2
PM2.5 Vitry vs. PM2.5 Gennevilliers 0.84 0.09 0.67 0.91 0.04 0.86
PM2.5 Vitry vs. PM2.5 Bobigny 0.89 0.10 0.63 0.94 0.04 0.91
PM10 Vitry vs. PM10 Gennevilliers 1.04 0.09 0.74 1.04 0.05 0.84
PM10 Vitry vs. PM10 Bobigny 1.02 0.11 0.63 0.93 0.07 0.73
PM1 SIRTA vs. PM2.5 Vitry 0.57 0.06 0.67 0.49 0.08 0.35
PM1 SIRTA vs. PM2.5 Gennevilliers 0.61 0.04 0.82 0.44 0.09 0.26
PM1 SIRTA vs. PM2.5 Bobigny 0.57 0.04 0.84 0.48 0.08 0.34
Meanwhile, surface measurements at SIRTA show rela-
tively high overall levels of ammonia: from 2 to 10 µg m−3 ,
which is higher than Paris urban background levels of 1–
3 µg m−3 shown by Petetin et al. (2016), but for the May 2010
to February 2011 period. On each of the days of the event
(26–30 March), morning daily maxima (up to 6–9 µg m−3 )
and smaller evening peaks (around 5 µg m−3 , Fig. 5) are
clearly depicted. Although both surface (Fig. 5b) and inte-
grated total column (Fig. 5a) ammonia measurements show
large concentrations, their daily evolution patterns are clearly
different. While total column values increase steadily during
the day until reaching a peak in the late afternoon, surface
ammonia moderately fluctuates during the day. These dif-
ferences may be associated with atmospheric processes or
interactions with the surface that modify ammonia concen-
trations differently as a function of altitude. This may be the
Figure 4. Particle matter concentrations measured at the surface case for vertical dilution of atmospheric constituents within
at the stations of Vitry, Bobigny, Gennevilliers and SIRTA, respec- the atmospheric boundary layer or the vertical variability of
tively, southeast, northeast, northwest and southwest of Paris. Parti- gas–particle partitioning related to relative humidity, temper-
cle concentrations in terms of PM2.5 and PM1 are provided, respec- ature and particle pH. These aspects are investigated in detail
tively, at the three Airparif stations and at the last one in the period in the following paragraphs.
between 26–31 March 2012. Vertical variations of atmospheric ammonia concentra-
tions may potentially be associated with temperature and rel-
on 28 March (4.6 × 1016 molec. cm−2 ). On 30 March, the ative humidity vertical profiles. As mentioned in Sect. 2.3,
diurnal evolution of NH3 total columns is more similar to dry conditions lead to volatilization of ammonia from ammo-
the first 2 measurement days (26–27 March). Steady to- nium particles, whereas humidity levels beyond the deliques-
tal columns around 1.5 × 1016 molec. cm−2 during the first cence point favor the inverse process (Seinfeld and Pandis,
1.5 h of the morning are followed by a decrease down to 2016). During the pollution event during 26–30 March, tem-
0.85 × 1016 molec. cm−2 around 11:00 UTC and afterwards perature shows the usual steady decrease with altitude from
an increase up to 2.5 × 1016 molec. cm−2 , which is lower the surface up to 2.5 km (see the median temperature pro-
than those observed during the 4 previous days. This clear file measured by radiosoundings launched at Trappes during
enhancement of ammonia total atmospheric columns dur- 26–30 March, Fig. 6a). Relative humidity varies greatly at
ing the day measured by OASIS is found to be typical of the lowest few kilometers of the atmosphere, typically in-
springtime polluted periods as already analyzed by Tournade creasing with altitude within the mixing boundary layer (up
et al. (2020) but not shown here (e.g., in March 2014 and to 1 to 1.5 km a.s.l., for the present case; see Fig. 6b). Dur-
March 2016). For all these years, the NH3 maximum in the ing 26–27 and 29 March, relative humidity increases from
afternoon is above 2 × 1016 molec. cm−2 (Tournadre et al., 25 % at the surface up to 35 %–40 % around 900 m a.s.l. and
2020). drops above 1000 m a.s.l. down to 10 %–20 %. On 28 March,
relative humidity is roughly 15 % higher than on the men-
https://doi.org/10.5194/acp-21-12091-2021 Atmos. Chem. Phys., 21, 12091–12111, 202112100 R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris
Figure 5. Observations of atmospheric ammoniac concentrations over the Paris region from 26 to 30 March 2012. The upper panel (a) dis-
plays total column retrievals at Créteil derived from OASIS observatory (48.79◦ N, 2.44◦ E) measurements during the day (∼ 07:00 and
16:00 UTC). The lower panel (b) displays continued ammonia surface concentration measurements from the AiRRmonia instrument near
Palaiseau (SIRTA observatory; 48.71◦ N, 2.20◦ E). This figure shows all available individual measurements from OASIS FTIR instrument
and AiRRmonia in situ analyzer.
tioned days up to 800 m a.s.l., above which it decreases down in Petetin et al. (2016) for the same period of the year. As
to 48 % and then rises up to 60 % at 1600 m a.s.l., drop- expected, results indicate that partitioning of ammonia into
ping down to 30 % at 2500 m a.s.l. In all these cases, rel- the particulate phase is favored with the decrease of tempera-
ative humidity up to 2500 m a.s.l. remains below the deli- ture. This temperature decrease is correlated to an increase of
quescence point (DRH) as shown in Fig. 6b, thus favoring relative humidity (while values remain below DRH). There-
the formation of NH3 by volatilization of ammonium par- fore, in equilibrium conditions (e.g., in absence of ammo-
ticles. This is also confirmed by relative humidity time se- nia and ammonium advection), ammonia likely decreases at
ries at different altitudes (200, 500, and 1000 m a.s.l.), recon- higher altitudes. Nevertheless, it should be noted that pH and
structed from all radiosounding measurements over the en- aerosol chemical composition also impact ammonium nitrate
tire event (launched from Trappes both at midday and mid- partitioning. PM1 was found to be neutralized during the pe-
night, Fig. 6c). This supports a hypothesis of an increase in riod study (Fig. S1 in the Supplement); therefore, we expect
ammonia amounts due to volatilization of ammonium nitrate a limited influence of ambient particle pH. However, our full
at higher altitudes. Relative humidity always remains below understanding is limited by the lack of HNO3 in situ and col-
the DRH (grey band), except for one single measurement at umn measurements.
1000 m on 30 March at noon. We also remark that during the As a conclusion, the decrease in T and the increase of RH
whole period relative humidity does not vary much vertically within the boundary layer height of 1–1.5 km with respect to
below 1000 m (except on 30 March) and that the most hu- ground shift the equilibrium to the aerosol phase. This does
mid conditions are found at midnights from 28 to 30 March. not explain the observed daytime column NH3 maximum,
No contrasting conditions between midday and midnight are which was not observed at the surface. This suggests that
either found for the vertical shape of relative humidity. We T and RH may not be the only drivers regarding the vertical
do not clearly point out any particular link or concomitant variability in NH3 concentrations. Other possible drivers are
temporal variation of relative humidity every 12 h at differ- analyzed in the following sections.
ent altitudes (Fig. 6c) and ammonia measurements (Fig. 5).
An additional analysis was performed with the ISOR- 3.4 Link between ammonia and ammonium particles
ROPIA II box model (Fountoukis and Nenes, 2007) to inves- over the Paris region
tigate the role of temperature and relative humidity in the par-
titioning of ammonium nitrate. The forward calculation used A joint analysis of the temporal evolution of ammonia and
measurements of the SIRTA site for NH+ −
4 , NO3 and NH3 ammonium particles provides further evidence of the role of
on 28 March 2012, representing the highest concentrations particle–gas conversion on the evolution of ammonia con-
on the studied period, as well as the meteorological param- centrations. As previously mentioned, volatilization leads to
eters. HNO3 concentrations were set constant from values concomitant increases of ammonia concentrations and de-
Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris 12101
Figure 6. (a) Median temperature (◦ C) over the period of interest in the vertical during midday. (b) Relative humidity (%) in the vertical
(midday only) from Trappes station and DRH based on the median temperature from (a). (c) Relative humidity evolution at different heights
(average over ±25 m) for all radiosoundings during 26–30 March, whereby the grey bar indicates the DRH lowest and highest values
corresponding to 170 and 2500 m altitude. DRH refers to deliquescence relative humidity.
creases of NH4 NO3 particles (the most abundant ammo- tions around 5 µg m−3 until midnight (Fig. 7c). Hourly con-
nium particles observed during this event; Petit et al., 2015). centrations of NH+ −
4 and NO3 show a similar evolution dur-
Complementary, the formation of ammonium nitrate parti- ing the day (Fig. 7c and e). They remain rather stable during
cles may be accompanied by a relative reduction of the abun- the night and early morning hours until 06:00 UTC (around
dance of its precursors (if they are not in excess) and thus ∼ 5 and ∼ 18 µg m−3 for, respectively, NH+ −
4 and NO3 ), with
ammonia and HNO3 . The following two subsections analyze a relative peak at 03:00 UTC. Afterwards, their concentra-
these processes for periods 1 and 2. tions show a small relative peak at 07:00 UTC, followed by
a strong reduction of 75 % during the day. Between noon
3.4.1 Local pollution regime during 26–27 March 2012 and 19:00 UTC, a rather stable daily minimum is seen for
(period 1) both ammonium and nitrate concentrations (of, respectively,
∼ 1 and ∼ 3 µg m−3 ). This is followed by a slight increase
Figure 7 presents hourly median measurements of ammo- (up to 3 and 7 µg m−3 , respectively). Meanwhile, sulfate
nia total column from OASIS and surface concentrations amounts remain low during P1 (below 1.5 µg m−3 , Fig. 7e).
of ammonia, ammonium (NH+ −
4 ), nitrate (NO3 ) and sul-
From the early morning until the afternoon, the strong re-
2−
fate (SO4 ) radicals measured at the SIRTA site (respec- duction of 75 % for both ammonium and nitrate abundances
tively, in Fig. 7a, c and e, for P1, and Fig. 7b, d and f, at the surface, which is not clearly observed for surface am-
for P2). During P1, hourly ammonia total columns measured monia (reducing by only 35 %), likely suggests the occur-
by OASIS show a stable level around 2 × 1016 molec. cm−2 rence of volatilization of ammonium particles. Probably, par-
until 10:00 UTC, after which a steady increase with larger ticle volatilization may be observable locally in the Paris re-
variability is observed during all the afternoon until reach- gion as this first period (P1) is characterized by a rather lo-
ing a median maximum of 3.4 × 1016 molec. cm−2 around cal pollution regime with limited transport of pollutants from
15:00 UTC (Fig. 7a). Surface ammonia concentrations other regions. Sustained volatilization of ammonium parti-
strongly vary during the night and clearly increase in the cles would lead to a steady enhancement of ammonia con-
morning hours with a relative maximum around 07:00 UTC centrations, as is clearly observed during almost all of the
up to 7 µg m−3 , likely related to evaporation from morning daytime by OASIS in terms of NH3 total columns. Addition-
dew (Petit et al., 2015; Wentworth et al., 2016) and it is fol- ally, volatilization of applied mineral fertilizers in the sur-
lowed by a steady decrease of about 35 % down to 4.5 µg m−3 rounding crop areas may also contribute to the daytime in-
around 13:00 UTC. A second relative enhancement of sur- crease of ammonia, as analyzed in detail during the same
face NH3 is seen during the afternoon at 17:00 UTC until period (March/April 2012) over crop fields located west of
reaching 6 µg m−3 , after which it fluctuates with concentra- Paris by Personne et al. (2015).
https://doi.org/10.5194/acp-21-12091-2021 Atmos. Chem. Phys., 21, 12091–12111, 202112102 R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris
Figure 7. Average diurnal evolution of total column NH3 (a, b), surface NH3 and NH+ −
4 (c, d) hourly median surface measurements of NO3
and SO−24 (e, f) for period 1 on the left side and period 2 on the right side. Hourly boxplots of NH3 total column retrieved from OASIS (a, b)
and hourly boxplots of NH3 from surface measurements show within the boxplot the median as a line in the plot, 25th and 75th percentile
as the lower and upper border of the box, and whiskers that extend to the most extreme data points, whereby outliers are separately marked
with a “+”.
Table 2. Meteorological variables at the surface and AOD during 26–27 March (period 1) and during 28–30 March (period 2), displayed by
the median, minimum and maximum values for temperature, relative humidity, deliquescence relative humidity, and wind speed and direction
– as well as AOD in its fine mode (FM) and coarse mode (CM).
period 1 period 2
Median Minimum Maximum Median Minimum Maximum
Temperature (◦ C) 16.2 10.8 21.8 14.8 10.5 21.0
Relative humidity (%) 41.8 19.0 66.0 54.8 26.5 77.0
Deliquescence relative humidity (%) 70.9 65.1 76.7 72.1 65.6 77.2
Wind speed (m s−1 ) 3.34 0.86 8.19 2.51 0.29 7.09
FM AOD 550 nm – Paris 0.10 0.05 0.14 0.29 0.13 0.55
CM AOD 550 nm – Paris 0.04 0.02 0.07 0.04 0.02 0.13
FM AOD 550 nm – SIRTA 0.10 0.04 0.15 0.32 0.10 0.62
CM AOD 550 nm – SIRTA 0.04 0.01 0.08 0.03 0.02 0.17
The fact that the daytime enhancement of NH3 is not that face relative humidity dropping down to 19 % at about
clearly reflected by its variability at surface level (Fig. 7c) 12:00 UTC, while the deliquescence relative humidity point
might be associated with an additional phenomenon that is 65 % (Fig. 8c). Local meteorological conditions are also
would reduce surface concentrations of gases and particles characterized by a gentle to fresh breeze, according to the
during daytime, such as vertical mixing within the atmo- Beaufort scale, with a dominant wind direction from the
spheric boundary layer (which is investigated in detail in north (see Fig. 8e and g, Table 2) and surface temperatures
Sect. 3.5). Volatilization of ammonium particles is also fa- ranging from 11 to 21 ◦ C.
vored by rather dry conditions during the day, with sur-
Atmos. Chem. Phys., 21, 12091–12111, 2021 https://doi.org/10.5194/acp-21-12091-2021R. D. Kutzner et al.: Diurnal evolution of total column and surface atmospheric ammonia in Paris 12103
Figure 8. Hourly median surface temperature (in ◦ C) (a, b), relative humidity (blue) and calculated deliquescence relative humidity (DRH;
black) (in %) (c, d), wind speed (in m s−1 ) (e, f), and wind direction (in degrees) (g, h) are presented in (a, c, e, g) for period 1 and
in (b, d, f, h) for period 2. Although temperature and relative humidity measurements originate from OASIS, wind speed and wind direction
data originate from the SIRTA supersite.
3.4.2 Pollution transported from the Benelux region steadily rise for 6 h until reaching 3.5 × 1016 molec. cm−2 at
and western Germany during 28–30 March 2012 16:00 UTC (Fig. 7b) with clearly more variability than dur-
(period 2) ing P1. Surface measurements of NH3 during the night show
a steady decrease from 5 µg m−3 at midnight to 3 µg m−3
at 05:00 UTC, with smaller variability as compared to the
P2 is characterized by the arrival of polluted air masses to the
same period of the day during P1. Surface NH3 concentra-
Paris region, originating from the Benelux and western Ger-
tions increase during the morning until reaching a maximum
many region (as remarked in Sect. 3.1, Fig. 3c, f and i) by
of 5.7 µg m−3 at 08:00 UTC, followed by a reduction down
rather weak winds (2.5 m s−1 , Fig. 8f) from the north and
to 4 µg m−3 2 h after (10:00 UTC) and then a second relative
northeast (Fig. 8h). Locally, meteorological conditions fa-
maximum of smaller amplitude (5 µg m−3 ) in the afternoon
vor particle formation during the night (maximum of RH of
(15:00 UTC, Fig. 7d). Ammonia emissions from the soil of
95 % above a DRH of 67 %, Fig. 8d) and volatilization dur-
surrounding crop areas may contribute to its enhancement
ing the day (minimum of RH of 27 % well below the DRH of
during the morning (Personne et al., 2015). It is also worth
66 %). A clear and stronger afternoon enhancement of am-
noting that forests surrounding the NH3 surface measure-
monia total columns is observed (Fig. 7b) as compared to
ment site at Palaiseau may act as local sinks of ammonia (as
the 2 previous days (P1, Fig. 7a). The median diurnal evo-
remarked by Behera et al., 2013; Hansen et al., 2015); this is
lution patterns of ammonia columns during P2 depict an
not the case for total column retrievals performed at Créteil.
early decrease from 1.5 × 1016 molec. cm−2 at 07:00 UTC
down to 1 × 1016 molec. cm−2 at 10:00 UTC. Then, they
https://doi.org/10.5194/acp-21-12091-2021 Atmos. Chem. Phys., 21, 12091–12111, 2021You can also read
