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Ammonia (NH3) is the most abundant alkaline compound in the atmosphere, with consequences for the environment, human health, and radiative forcing. In urban environments, it is known to play a key role in the formation of secondary aerosols through its reactions with nitric and sulfuric acids. However, there are only a few studies about NH3 in Mexico City. In this work, atmospheric NH3 was measured over Mexico City between 2012 and 2020 by means of ground-based solar absorption spectroscopy using Fourier transform infrared (FTIR) spectrometers at two sites (urban and remote). Total columns of NH3 were retrieved from the FTIR spectra and compared with data obtained from the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument. The diurnal variability of NH3 differs between the two FTIR stations and is strongly influenced by the urban sources. Most of the NH3 measured at the urban station is from local sources, while the NH3 observed at the remote site is most likely transported from the city and surrounding areas. The evolution of the boundary layer and the temperature play a significant role in the recorded seasonal and diurnal patterns of NH3. Although the vertical columns of NH3 are much larger at the urban station, the observed annual cycles are similar for both stations, with the largest values in the warm months, such as April and May. The IASI measurements underestimate the FTIR NH3 total columns by an average of 32.2±27.5 % but exhibit similar temporal variability. The NH3 spatial distribution from IASI shows the largest columns in the northeast part of the city. In general, NH3 total columns over Mexico City measured at the FTIR stations exhibited an average annual increase of 92±3.9×1013 molecules cm−2 yr−1 (urban, from 2012 to 2019) and 8.4±1.4×1013 molecules cm−2 yr−1 (remote, from 2012 to 2020), while IASI data within 20 km of the urban station exhibited an average annual increase of 38±7.6×1013 molecules cm−2 yr−1 from 2008 to 2018.

Ammonia (NH3) is an important air pollutant which, as precursor of fine particulate matter, raises public health issues. This study analyzes 2.5-years of NH3 observations derived from ground-based (miniDOAS) and satellite (IASI) remote sensing instruments to quantify, for the first time, temporal variabilities (from interannual to diurnal) of NH3 concentrations in Paris. The IASI and miniDOAS datasets are found to be in relatively good agreement (R > 0.70) when atmospheric NH3 concentrations are high and driven by regional agricultural activities. Over the investigated period (January 2020–June 2022), NH3 average concentrations in Paris measured by the miniDOAS and IASI are 2.23 μg.m−3 and 7.10 × 1015 molecules.cm−2, respectively, which are lower or equivalent to those documented in urban areas. The seasonal and monthly variabilities of NH3 concentrations in Paris are driven by sporadic agricultural emissions influenced by meteorological conditions, with NH3 concentrations in spring up to 2 times higher than in other seasons. The potential source contribution function (PSCF) reveals that the close (100–200 km) east and northeast regions of Paris constitute the most important potential emission source areas of NH3 in the megacity. Weekly cycles of NH3 derived from satellite and ground-based observations show different ammonia sources in Paris. In spring, agriculture has a major influence on ammonia concentrations and, in the other seasons, multi-platform observations suggest that ammonia is also controlled by traffic-related emissions. In Paris, the diurnal cycle of NH3 concentrations is very similar to the one of NO2, with morning enhancements coincident with intensified road traffic. NH3 evening enhancements synchronous with rush hours are also monitored in winter and fall. NH3 concentrations measured during the weekends are consistently lower than NH3 concentrations measured during weekdays in summer and fall. This is a further evidence of a significant traffic source of NH3 in Paris.

Ammonia (NH3) is mainly emitted in the atmosphere by anthropogenic activities, especially by agriculture. Excess emissions greatly disturb ecosystems, biodiversity, and air quality. Despite our awareness of these deleterious consequences, NH3 concentrations are increasing in most industrialized countries. This underlines the need for more stringent regulations and good knowledge of the species gained through effective monitoring.Since a decade, NH3 is monitored from space, daily and globally, with thermal infrared sounders. However, their coarse spatial resolution (above 10 km) renders accurate quantification of NH3 sources particularly challenging. Indeed, only the largest and most isolated NH3 point sources have been identified and quantified from current observations and often only by exploiting long-term averages. To address the urgent need for better constraining NH3 emissions, a new satellite, called Nitrosat, has been proposed in response to the 11th ESA’s Earth Explorer call. The mission aims at mapping simultaneously NO2 and NH3 at a spatial resolution of 500 m at a global scale. With the support of ESA, almost 30 aircraft demonstration flights took place in Europe between 2020 and 2022. These flights mapped gapless areas of at least 10 by 20 km containing various sources of NO2 and NH3 using two instruments: the SWING instrument targeting NO2 in the UV-VIS and Hyper-Cam LW measuring infrared spectra to observe NH3.Here we present NH3 observations from campaigns performed in Italy in spring 2022. The Po Valley was the main target, as it is the largest (agricultural) hotspot of NH3 in Europe. Despite the presence of large background concentrations in the Po Valley, we show that the infrared measurements are able to expose a multitude of local agricultural hotspots such as cattle farms. A particularly successful campaign covering the region from Vetto to Colorno demonstrates measurement sensitivity to the gradual increase of NH3 background concentrations outside and inside the Po Valley. We also discuss flights carried out further south in Italy targeting other emissions of NH3, such as those from a soda ash plant, and the emissions from a fertilizer release experiment that was organized in collaboration with a farmer. We present the measurements both at their native horizontal resolution of 4 m and downsampled at the 500 m resolution of Nitrosat.

Short-lived atmospheric pollutants mainly reside in the planetary boundary layer (PBL). In recent years, the sensitivity of high-resolution infrared sounders to the PBL has been amply demonstrated, most notably through observations of local emission sources of sulphur dioxide (SO2), carbon monoxide (CO) and ammonia (NH3). However, sensitivity of infrared sounders to the PBL varies strongly as a function of thermal contrast (TC), the temperature difference between the Earth’s skin temperature and the temperature of the atmosphere. Enhanced contrast, typically seen during daytime when the surface is typically (much) warmer than the air, provides favourable measurement conditions. At night, TC is smaller, and can even become negative, providing again favourable measurement conditions. More generally speaking, TC is highly variable in both time (inter and intraday) and space. Up to now, no study has provided insight in the global statistical behaviour of the TC or answered the question when and where thermal infrared sounders experience optimal measurement conditions.Here we combine the Copernicus Global Land Services land surface temperature (LST) dataset, derived from geostationary satellite measurements, with air temperatures from the ERA5 reanalysis dataset to obtain a global TC dataset at high temporal (1 hour) and high spatial (31 km) resolution. TC is analysed at two different altitudes, the standard meteorological height of 2 meters, and at half the boundary layer height. In addition to the ERA5-based dataset, we also present an additional TC dataset obtained with data from a global constellation of meteorological stations.We analyse and present statistics on the dependence of TC as function of time of the day, time of the year and land cover. These provide constraints on the time windows and boundary conditions (e.g., land cover type) for which the sensitivity of the TIR instruments is best. It also allows optimal planning of overpass times for future infrared satellite sounders or the organization of aerial measurement campaigns for near-surface pollutants. Finally, this unique dataset can be used to statistically assess the measurement sensitivity of infrared sounders.

Ammonia (NH3) is an atmospheric pollutant mainly emitted by the agricultural sector. It is a precursor of fine particles (PM2.5) and therefore has a major effect on public health, and climate change. The volatilization process of NH3 and its lifetime in the atmosphere, as well as its transformation into particles, are poorly constrained and strongly depend on meteorological parameters, in particular temperature.Although current satellite measurements have evaluated NH3 spatio-temporal variabilities at various scales (global, regional, and local), observations of NH3 diurnal variability and their diurnal variability and dependence to temperature are poorly constrained. This strongly influences our ability to correctly simulate NH3 emissions and associated particulate pollution events in atmospheric models.The IRS (InfraRed Sounder) instrument which will be launched on the MTG (Meteosat Third Generation) satellite into geostationary orbit in late 2024, will offer the ability to deepen this analysis with more frequent measurements (every 30-45 minutes over Europe and Africa) and better spatially resolved observations (4 km x 4 km at the Equator).In this presentation, we show the potential of the new geostationary IRS-MTG mission to assess spatio-temporal variabilities of ammonia and temperature focusing on a case study over the high NH3 emitted region of Brittany (France). Using atmospheric states simulated using the CHIMERE chemistry-transport model at the effective spatial resolution of IRS over Brittany, synthetic spectra are computed using the 4A/OP radiative transfer model. NH3 measurement-sensitivity of the future IRS-MTG mission is discussed with regards to the presently available IASI observations.

Atmospheric ammonia (NH3) is a precursor to fine particulate matter and a source of nitrogen (N) deposition that can adversely affect ecosystem health. The main sources of NH3 – agriculture and biomass burning – are undergoing are or expected to undergo substantial changes in Africa. Although evidence of increasing NH3 over parts of Africa has been observed, the mechanisms behind these trends are not well understood. Here we use observations of atmospheric NH3 vertical column densities (VCDs) from the Infrared Atmospheric Sounding Interferometer (IASI) along with other satellite observations of the land surface and atmosphere to evaluate how NH3 concentrations have changed over Africa from 2008 through 2018, and what has caused those changes. In West Africa NH3 VCDs are observed to increase during the late dry season, with increases of over 6 % yr−1 in Nigeria during February and March (p

Ammonia (NH3) is the most abundant alkaline component in the atmosphere. Changes in NH3 concentrations have important implications for atmospheric chemistry, air quality, and ecosystem integrity. We present a long-term ammonia (NH3) assessment in the Western and Central Africa region within the framework of the International Network to study Deposition and Atmospheric chemistry in Africa (INDAAF) program. We analyze seasonal variations and trends of NH3 concentrations and total columns densities along an African ecosystem transect spanning dry savannas in Banizoumbou, Niger and Katibougou, Mali, wet savannas in Djougou, Benin and Lamto, Côte d’Ivoire, and forests in Bomassa, Republic of Congo and Zoétélé, Cameroon. We use a 21-year record of observations (1998–2018) from INDAAF passive samplers and 11-year record of observations (2008–2018) of atmospheric vertical column densities from the Infrared Atmospheric Sounding Interferometer (IASI) to evaluate NH3 ground-based concentrations and total column densities, respectively. Annual mean ground-based NH3 concentrations are around 5.7–5.8 ppb in dry savannas, 3.5–4.7 ppb in wet savannas and 3.4–5.6 ppb in forests. These results suggest that NH3 emissions from precipitation-induced pulses and volatilization from animal excreta are important emission sources in dry savannas, and biomass burning and agricultural sources are important sources in wet savanna and forest ecosystems. NH3 total column densities clearly show that the biomass burning source is the most important source in the Lamto wet savanna ecosystem. Annual IASI NH3 total column densities are 10.1–11.0x1015 molec cm-2 in dry savanna, 16.5–21.4x1015 molec cm-2 in wet savanna and 14.3–15.1x1015 molec cm-2 in forest stations. Non-parametric statistical Mann-Kendall trend tests applied to annual data show that ground-based NH3 concentrations increase at Bomassa (+2.56 % yr-1), but decrease at Zoétélé (-2.95 % yr-1) over the 21-year period. The 11-year period of IASI NH3 total column density measurements show yearly increasing trends at Katibougou (+3.98 % yr-1) and Djougou (+2.24 % yr-1). At Zoétélé, we calculated an increasing trend of leaf area index associated to a significant anticorrelation with ground-based NH3 concentrations. Leaf area index increase could enhance deposition processes and could contribute to the decrease of ground-based NH3 concentrations.

Atmospheric emissions of reactive nitrogen in the form of nitrogen dioxide (NO) and ammonia (NH) worsen air quality and upon deposition, dramatically affect the environment. Recent infrared satellite measurements have revealed that NH emitted by industries are an important and underestimated emission source. Yet, to assess these emissions, current satellite sounders are severely limited by their spatial resolution. In this paper, we analyse measurement data recorded in a series of imaging surveys that were conducted over industries in the Greater Berlin area (Germany). On board the aircraft were the Telops Hyper-Cam LW, targeting NH measurements in the longwave infrared at a resolution of 4 m and the SWING+ spectrometer targeting NO measurements in the UV–Vis at a resolution of 180 m. Two flights were carried out over German’s largest production facility of synthetic NH , urea and other fertilizers. In both cases, a large NH plume was observed originating from the factory. Using a Gaussian plume model to take into account plume rise and dispersion, coupled with well-established radiative transfer and inverse methods, we retrieve vertical column densities. From these, we calculate NH emission fluxes using the integrated mass enhancement and cross-sectional flux methods, yielding consistent emissions of the order of 2200 t yr−1 for both flights, assuming constant fluxes across the year. These estimates are about five times larger than those reported in the European Pollutant Release and Transfer Register (E-PRTR) for this plant. In the second campaign, a co-emitted NO plume was measured, likely related to the production of nitric acid at the plant. A third flight was carried out over an area comprising the cities of Staßfurt and Bernburg. Several small NH plumes were seen, one over a production facility of mineral wool insulation, one over a sugar factory and two over the soda ash plants in Staßfurt and Bernburg. A fifth and much larger plume was seen to originate from the sedimentation basins associated with the soda ash plant in Staßfurt, indicating rapid volatilization of ammonium rich effluents. We use the different measurement campaigns to simulate measurements of Nitrosat, a potential future satellite sounder dedicated to the sounding of reactive nitrogen at a resolution of 500 m. We demonstrate that such measurements would allow accurately constraining emissions in a single overpass, overcoming a number of important drawbacks of current satellite sounders.

Ammonia (NH3) is one of the most important gases emitted from agricultural practices. It affects air quality and the overall climate, and in turn influenced by long term climate trends as well as by short term fluctuations in local and regional meteorology. Previous studies have established the capability of the Infrared Atmospheric Sounding Interferometer (IASI) series of instruments aboard the Metop satellites to measure ammonia from space since 2007. In this study, we explore the interactions between atmospheric ammonia, land and meteorological variability, and long-term climate trends in Europe. We investigate the emission potential (Γsoil) of ammonia from the soil, which describes the soil – atmosphere ammonia exchange. Γsoil is generally calculated in-field or in laboratory experiments; here, and for the first time, we investigate a method which assesses it remotely using satellite data, reanalysis data products, and model simulations. We focus on ammonia emission potential during March 2011, which marks the start of growing season in Europe. Our results show that Γsoil ranges from 2 × 103 to 9.5 × 104 (dimensionless) in a fertilized cropland, such as in the North European Plain, and is of the order of 10–102 in a non-fertilized soil (e.g. forest and grassland). These results agree with in-field measurements from the literature, suggesting that our method can be used in other seasons and regions in the world. However, some improvements are needed in the determination of mass transfer coefficient k (m s-1), which is a crucial parameter to derive Γsoil. Using a climate model, we estimate the expected increase in ammonia columns by the end of the century based on the increase in skin temperature (T skin), under two different climate scenarios. Ammonia columns are projected to increase by up to 50 %, particularly in Eastern Europe, under the SSP2-4.5 scenario, and might even double (increase of 100 %) under the SSP5-8.5 scenario. The increase in skin temperature is responsible for a formation of new hotspots of ammonia in Belarus, Ukraine, Hungary, Moldova, parts of Romania, and Switzerland.

Volatile organic compounds are emitted abundantly from a variety of natural and anthropogenic sources. However, in excess, they can severely degrade air quality. Their fluxes are currently poorly represented in inventories due to a lack of constraints from global measurements. Here, we track from space over 300 worldwide hotspots of ethylene, the most abundant industrially produced organic compound. We identify specific emitters associated with petrochemical clusters, steel plants, coal-related industries, and megacities. Satellite-derived fluxes reveal that the ethylene emissions of the industrial sources are underestimated or missing in the state-of-the-art Emission Database for Global Atmospheric Research (EDGAR) inventory. This work exposes global emission point-sources of a short-lived carbonated gas, complementing the ongoing large-scale efforts on the monitoring of inorganic pollutants.

Megacities can experience high levels of fine particulate matter (PM2.5) pollution linked to ammonia (NH3) mainly emitted from agricultural activities. Here, we investigate such pollution in the cities of Paris, Mexico, and Toronto, each of which have distinct emission sources, agricultural regulations, and topography. Ten years of measurements from the infrared atmospheric sounding interferometer (IASI) are used to assess the spatiotemporal NH3 variability over and around the three cities. In Europe and North America, we determine that temperature is associated with the increase in NH3 atmospheric concentrations with a coefficient of determination (r2) of 0.8 over agricultural areas. The variety of the NH3 sources (industry and agricultural) and the weaker temperature seasonal cycle in southern North America induce a lower correlation factor (r2=0.5). The three regions are subject to long-range transport of NH3, as shown using HYSPLIT cluster back trajectories. The highest NH3 concentrations measured at the city scale are associated with air masses coming from the surrounding and north/northeast regions of Paris, the south/southwest areas of Toronto, and the southeast/southwest zones of Mexico City. Using NH3 and PM2.5 measurements derived from IASI and surface observations from 2008 to 2017, annually frequent pollution events are identified in the three cities. Wind roses reveal statistical patterns during these pollution events with dominant northeast/southwest directions in Paris and Mexico City, and the transboundary transport of pollutants from the United States in Toronto. To check how well chemistry transport models perform during pollution events, we evaluate simulations made using the GEOS-Chem model for March 2011. In these simulations we find that NH3 concentrations are underestimated overall, though day-to-day variability is well represented. PM2.5 is generally underestimated over Paris and Mexico City, but overestimated over Toronto.

Ammonia (NH3) is the most abundant alkaline compound in the atmosphere, with consequences for the environment, human health, and radiative forcing. In urban environments, it is known to play a key role in the formation of secondary aerosols through its reactions with nitric and sulphuric acids. However, there are only a few studies about NH3 in Mexico City. In this work, atmospheric NH3 was measured over Mexico City between 2012 and 2020 by means of ground-based solar absorption spectroscopy using Fourier transform infrared (FTIR) spectrometers at two sites (urban and remote). Total columns of NH3 were retrieved from the FTIR spectra and compared with data obtained from the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument. The diurnal variability of NH3 differs between the two FTIR stations and is strongly influenced by the urban sources. Most of the NH3 measured at the urban station is from local sources, while the NH3 observed at the remote site is most likely transported from the city and surrounding areas. The evolution of the boundary layer and the temperature play a significant role in the recorded seasonal and diurnal patterns of NH3. Although the vertical columns of NH3 are much larger at the urban station, the observed annual cycles are similar for both stations, with the largest values in the warm months, such as April and May. The IASI measurements underestimate the FTIR NH3 total columns by an average of 32.2 ± 27.5 % but exhibit similar temporal variability. The NH3 spatial distribution from IASI shows the largest columns in the northeast part of the city. In general, NH3 total columns over Mexico City exhibited an average annual increase of 92 ± 3.9 x 1013 molecules/cm2 yr (urban) and 8.4 ± 1.4 x 1013 molecules/cm2 yr (remote) was observed in Mexico City at both FTIR stations and a decadal increase of 62 % with IASI data.

The presence of a weekly cycle in the abundance of an atmospheric constituent is a typical fingerprint for the anthropogenic nature of its emission sources. However, while ammonia is mainly emitted as a consequence of human activities, a weekly cycle has never been detected in its abundances at large scale. We expose here for the first time the presence of a weekend effect in the NH3 total columns measured by the IASI satellite sounder over the main agricultural source regions in Europe: northwestern Europe (Belgium-the Netherlands-northwest Germany), the Po Valley, Brittany, and, to a lesser extent, the Ebro Valley. A decrease of 15% relative to the weekly mean is seen on Sunday–Monday observations in northwestern Europe, as a result of reduced NH3 emissions over the weekend. This is confirmed by in situ NH3 concentration data from the National Air Quality Monitoring Network in the Netherlands, where an average reduction of 10% is found around midnight on Sunday. The identified weekend effect presents a strong seasonal variability, with two peaks, one in spring and one in summer, coinciding with the two main (manure) fertilization periods. In spring, a reduction on Sunday–Monday up to 53 and 26% is found in the NH3 satellite columns and in situ concentrations, respectively, as fertilization largely drives atmospheric NH3 abundances at this time of the year.

Tropical cities are experiencing rapid growth but lack routine air pollution monitoring to develop prescient air quality policies. Here, we conduct targeted sampling of recent (2000s to 2010s) observations of air pollutants from space-based instruments over 46 fast-growing tropical cities. We quantify significant annual increases in nitrogen dioxide (NO 2 ) (1 to 14%), ammonia (2 to 12%), and reactive volatile organic compounds (1 to 11%) in most cities, driven almost exclusively by emerging anthropogenic sources rather than traditional biomass burning. We estimate annual increases in urban population exposure to air pollutants of 1 to 18% for fine particles (PM 2.5 ) and 2 to 23% for NO 2 from 2005 to 2018 and attribute 180,000 (95% confidence interval: −230,000 to 590,000) additional premature deaths in 2018 (62% increase relative to 2005) to this increase in exposure. These cities are predicted to reach populations of up to 80 million people by 2100, so regulatory action targeting emerging anthropogenic sources is urgently needed.

Emissions of ammonia (NH3) to the atmosphere impact human health, climate, and ecosystems through their critical contributions to secondary aerosol formation. Estimation of NH3 emissions is associated with large uncertainties because of inadequate knowledge about agricultural sources. Here, we use satellite observations from the Infrared Atmospheric Sounding Interferometer (IASI) and simulations from the GEOS-Chem model to constrain global NH3 emissions over the period of 2008–2018. We update the prior NH3 emission fluxes with the ratio between biases in simulated NH3 concentrations and effective NH3 lifetimes against the loss of the NHx family. In contrast to about a factor of two discrepancies between top-down and bottom-up emissions found in previous studies, our method results in a global land NH3 emission of 79 (71–96) Tg a-1, ~30 % higher than the bottom-up estimates. Regionally, we find that the bottom-up inventory underestimates NH3 emissions over the South America and tropical Africa by 60–70 %, indicating under-representation of agricultural sources in these regions. We find a good agreement within 10 % between bottom-up and top-down estimates over the U.S., Europe and eastern China. Our results also show significant increases in NH3 emissions over India (13 % decade-1), tropical Africa (33 % decade-1), and South America (18 % decade-1) during our study period, consistent with the intensifying agricultural activities in these regions in the past decade. We find that inclusion of SO2 column observed by satellite is crucial for more accurate inference of NH3 emission trends over important source regions such as India and China where SO2 emissions have changed rapidly in recent years.

Ammonia (NH3) is a key species in the atmosphere, playing a crucial role in air quality and climate through the formation of sulfate and nitrate particles. Moreover, NH3 surface deposition alters ecosystems. About 85% of NH3 global anthropogenic emissions are related to food and feed production and in particular to the use of mineral fertilizers and manure management. Even though the estimate of the emissions from livestock can reach 36 Tg N/yr, they are generally not represented explicitly in global land surface models. Most global chemistry transport models rely on bottom-up emission inventories subject to large uncertainties. Our objective consists of replacing these external emissions data by dynamical emissions computed by ORCHIDEE, a terrestrial ecosystem model including the carbon and the nitrogen cycles. This new version of the ORCHIDEE model includes a detailed integrated scheme for livestock management, from housing and storage to grazing emissions. Ultimately, our work aims at developing an interactive nitrogen cycle model in a coupled climate-chemistry-vegetation model in order to investigate the impact of NH3 emissions from livestock on atmospheric chemistry and climate, and the associated feedbacks.In this study, we describe and present global NH3 emissions from livestock calculated based on the new version of the ORCHIDEE land surface model . We evaluate NH3 emissions simulated by ORCHIDEE with previous inventories and model estimates. An analysis of key parameters driving the soil NH3 emissions (pH of the manure, the timing of the N application, the surface atmospheric concentration etc… ) have also been performed in order to assess the sensitivity of the simulated emissions. Last, we investigate the impact of prescribing these new simulated emissions on atmospheric chemistry, using the global atmospheric chemistry transport model LMDZ-OR-INCA. The simulated NH3 atmospheric columns are evaluated by global and regional comparisons with the spaceborne IASI instrument measurements. The products used are monthly gridded NH3 distributions using morning observations of IASI-(Metop)A and IASI-(Metop)B for the period 2011-2017. In addition, we compare the ammonia atmospheric columns simulated based on the dynamical livestock emissions and based on reference bottom-up emission inventories. Finally, we investigate the impact of the different NH3 emission inventories on key atmospheric species concentrations.

Agricultural emissions of ammonia (NH3) impact air quality, human health, and the vitality of aquatic and terrestrial ecosystems. In the UK, there are few direct policies regulating anthropogenic NH3 emissions and development of sustainable mitigation measures necessitates reliable emissions estimates. Here, we use observations of column densities of NH3 from two space-based sensors (IASI and CrIS) with the GEOS-Chem model to derive top-down NH3 emissions for the UK at fine spatial (similar to 10 km) and time (monthly) scales. We focus on March-September when there is adequate spectral signal to reliably retrieve NH3. We estimate total emissions of 272 Gg from IASI and 389 Gg from CrIS. Bottom-up emissions are 27% less than IASI and 49% less than CrIS. There are also differences in seasonality. Top-down and bottom-up emissions agree on a spring April peak due to fertilizer and manure application, but there is also a comparable summer July peak in the top-down emissions that is not in the bottom-up emissions and appears to be associated with dairy cattle farming. We estimate relative errors in the top-down emissions of 11%-36% for IASI and 9%-27% for CrIS, dominated by column density retrieval errors. The bottom-up versus top-down emissions discrepancies estimated in this work impact model predictions of the environmental damage caused by NH3 emissions and warrant further investigation.

International audience; Ammonia (NH3) and nitrogen oxides (NOx: nitrogen dioxide [NO2] + nitric oxide [NO]) play important roles in atmospheric chemistry. Throughout most of Africa, emissions of these gases are predominantly from soils and biomass burning. Here we use observations of tropospheric NO2 vertical column densities (VCDs) from the Ozone Monitoring Instrument from 2005 through 2017 and atmospheric NH3 VCDs from the Infrared Atmospheric Sounding Interferometer from 2008 through 2017 to evaluate seasonal variation of NO2 and NH3 VCDs across Africa and in seven African ecoregions. In regions where mean annual precipitation (MAP) is under 500 mm yr−1, we find that NO2 and NH3 VCDs are positively related to monthly precipitation, and where MAP is between 500 and 1,750 mm yr−1 or higher, NO2 VCDs are negatively related to monthly precipitation. In dry ecoregions, temperature and precipitation were important predictors of NH3 and NO2 VCDs, likely related to variation in soil emissions. In mesic ecoregions, monthly NO2 VCDs were strongly related to burned area, suggesting that biomass burning drives seasonality. NH3 VCDs in mesic ecoregions were positively related to both monthly temperature and monthly carbon monoxide (CO) VCDs, suggesting that a mixture of soil and biomass burning emissions influenced NH3 seasonality. In northern mesic ecoregions, monthly temperature explained most of the variance in monthly NH3 VCDs, suggesting that soil sources, including animal excreta, determined NH3 seasonality. In southern mesic ecoregions, monthly CO VCDs explained more variation in NH3 VCDs than temperature, suggesting that biomass burning may have greater influence over NH3 seasonality.

As a precursor of atmospheric aerosols, ammonia (NH3) is one of the primary gaseous air pollutants. Given its short atmospheric lifetime, ambient NH3 concentrations are dominated by local sources. In a recent study, Van Damme et al. (2018) have highlighted the importance of NH3 point sources, especially those associated with feedlots and industrial ammonia production. Their emissions were shown to be largely underestimated in bottom-up emission inventories. The discovery was made possible thanks to the use of oversampling techniques applied to 9 years of global daily IASI NH3 satellite measurements. Oversampling allows one to increase the spatial resolution of averaged satellite data beyond what the satellites natively offer. Here we apply for the first time superresolution techniques, which are commonplace in many fields that rely on imaging, to measurements of an atmospheric sounder, whose images consist of just single pixels. We demonstrate the principle on synthetic data and on IASI measurements of a surface parameter. Superresolution is a priori less suitable to be applied on measurements of variable atmospheric constituents, in particular those affected by transport. However, by first applying the wind-rotation technique, which was introduced in the study of other primary pollutants, superresolution becomes highly effective in mapping NH3 at a very high spatial resolution. We show that plume transport can be revealed in greater detail than what was previously thought to be possible. Next, using this wind-adjusted superresolution technique, we introduce a new type of NH3 map that allows tracking down point sources more easily than the regular oversampled average. On a subset of known emitters, the source could be located within a median distance of 1.5 km. We subsequently present a new global point-source catalog consisting of more than 500 localized and categorized point sources. Compared to our previous catalog, the number of identified sources more than doubled. In addition, we refined the classification of industries into five categories – fertilizer, coking, soda ash, geothermal and explosives industries – and introduced a new urban category for isolated NH3 hotspots over cities. The latter mainly consists of African megacities, as clear isolation of such urban hotspots is almost never possible elsewhere due to the presence of a diffuse background with higher concentrations. The techniques presented in this paper can most likely be exploited in the study of point sources of other short-lived atmospheric pollutants such as SO2 and NO2.

Ammonia (NH3) is an essential reactive nitrogen species in the biosphere and through its use in agriculture in the form of fertilizer (important for sustaining humankind). The current emission levels, however, are up to 4 times higher than in the previous century and continue to grow with uncertain consequences to human health and the environment. While NH3 at its current levels is a hazard to environmental and human health, the atmospheric budget is still highly uncertain, which is a product of an overall lack of measurements. The capability to measure NH3 with satellites has opened up new ways to study the atmospheric NH3 budget. In this study, we present the first estimates of NH3 emissions, lifetimes and plume widths from large (>∼5 kt yr−1) agricultural and industrial point sources from Cross-track Infrared Sounder (CrIS) satellite observations across the globe with a consistent methodology. The same methodology is also applied to the Infrared Atmospheric Sounding Interferometer (IASI) (A and B) satellite observations, and we show that the satellites typically provide comparable results that are within the uncertainty of the estimates. The computed NH3 lifetime for large point sources is on average 2.35±1.16 h. For the 249 sources with emission levels detectable by the CrIS satellite, there are currently 55 locations missing (or underestimated by more than an order of magnitude) from the current Hemispheric Transport Atmospheric Pollution version 2 (HTAPv2) emission inventory and only 72 locations with emissions within a factor of 2 compared to the inventories. The CrIS emission estimates give a total of 5622 kt yr−1, for the sources analyzed in this study, which is around a factor of ∼2.5 higher than the emissions reported in HTAPv2. Furthermore, the study shows that it is possible to accurately detect short- and long-term changes in emissions, demonstrating the possibility of using satellite-observed NH3 to constrain emission inventories.

Air pollution reaching hazardous levels in many Chinese cities has been a major concern in China over the past decades. New policies have been applied to regulate anthropogenic pollutant emissions, leading to changes in atmospheric composition and in particulate matter ( PM ) production. Increasing levels of atmospheric ammonia columns have been observed by satellite during recent years. In particular, observations from the Infrared Atmospheric Sounding Interferometer (IASI) reveal an increase of these columns by 15 % and 65 % from 2011 to 2013 and 2015, respectively, over eastern China. In this paper we performed model simulations for 2011, 2013 and 2015 in order to understand the origin of this increase and to quantify the link between ammonia and the inorganic components of particles: NH 4 ( p ) + / SO 4 ( p ) 2 - / NO 3 ( p ) - . Interannual change of meteorology can be excluded as a reason: year 2015 meteorology leads to enhanced sulfate production over eastern China, which increases the ammonium and decreases the ammonia content, which is contrary to satellite observations. Reductions in SO2 and NOx emissions from 2011 to 2015 of 37.5 % and 21 % respectively, as constrained from satellite data, lead to decreased inorganic matter (by 14 % for NH 4 ( p ) + + SO 4 ( p ) 2 - + NO 3 ( p ) - ). This in turn leads to increased gaseous NH3(g) tropospheric columns by as much as 24 % and 49 % (sampled corresponding to IASI data availability) from 2011 to 2013 and 2015 respectively and thus can explain most of the observed increase.

Ammonia (NH3) is a key precursor of haze particles and fine particulate matter (PM2.5) and its spatiotemporal variabilities are poorly constrained. In this study, we present measurements of NH3 over the Indian subcontinent region from the Infrared Atmospheric Sounder Interferometer (IASI) and Cross-track Infrared Sounder (CrIS) satellite instruments. This region exhibits a complex emission profile due to the number of varied sources, including crop burning, fossil fuel combustion, fertilizer application, livestock and industrial sources. Observations from the CrIS and IASI instruments are oversampled to a resolution of 0.02° × 0.02°. Five regions with distinct spatiotemporal NH3 profiles are determined using k-means clustering. Maximum NH3 columns are seen in July over the western India with column densities of 6.2 × 1017 mol cm−2 and 7.2 × 1017 mol cm−2 respectively for IASI and CrIS. The seasonality of measured NH3 columns show annual maxima occurring in spring in Eastern India and Bangladesh and in mid-summer for the western Indo-Gangetic plain. Our observational constraints suggest that the impact of local farming practices on NH3 emissions is not well captured in emission inventories such as Coupled Model Intercomparison Project Phase 6 (CMIP6), which exhibits peaks in the late spring and autumn. The spatial variability in the seasonal patterns of NH3 is also not captured by the single emissions profile used in CMIP6 for India. The high-resolution maps obtained from these measurements can be used to improve NH3 emission inventories in order to understand its sources for more accurate predictions of air quality in the Indian subcontinent. Our study points to the need for regionally specific emissions inventories for short-lived species such as NH3 that have heterogeneous emissions profiles due to specific agricultural practices and other emission source characteristics.

International audience; Limiting excess atmospheric ammonia (NH3) is one of the great challenges for humanity in the 21th century, but can only be achieved with adequate monitoring means in place. Here, we report the first NH3 measurements from the Geostationary Interferometric Infrared Sounder (GIIRS) onboard the Chinese FY-4A satellite. The instrument scans almost all of Asia ten times per day. We show that GIIRS’ unprecedented temporal sampling can be exploited to measure diurnal and nocturnal variations of NH3 and demonstrate this on two case studies over Punjab and the North China Plain. Day–night variations are found to be almost absent in winter, but can reach a factor 2–3 in the warmer months. These case studies are very promising given the future landscape of geostationary sounders, but also show that improved knowledge on lower tropospheric air temperatures and the vertical profile of NH3 is key to better exploit their measurements.

Atmospheric sounding in the infrared has, for a long time, mainly been dedicated to meteorology. The operation of hyperspectral sounders has remarkably served this application area in the last two decades, up to the level that these instruments have become the dominant contributors to numerical weather forecast. Even more remarkable is, however, how the hyperspectral infrared sounders have fostered the fields of atmospheric chemistry and climate, thanks to the measurements of a large series of trace gases in the troposphere and stratosphere (see infographics in Figure 1 and e.g. [1]). In Europe, major advances have been made by exploiting radiance record of the Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop platform series, which started in 2006 and is expected to continue until 2024 at least. The long time series of available IASI measurements and its remarkable stability over time has in particular allowed characterizing the inter-annual variability of several reactive species (ozone -O 3 -, carbon monoxide -CO-, ammonia -NH 3 -), to isolate significant trends in the troposphere and the stratosphere (for 03), and to trace these to emission reductions or to changes in our environment and climate (e.g. [2], [3]). Another key achievement made with IASI lies in the detection and characterization of local point sources from agriculture and industry in averaged distributions [4].

Anthropogenic atmospheric emissions of the reactive nitrogen components nitrogen dioxide (NO2) and ammonia (NH3) have majorly altered the global nitrogen cycle in the past 100 years, with devastating consequences to biodiversity, soil, water and air quality. Thanks to effective legislation, NO2 emissions are declining worldwide. Unfortunately, this is not the case for NH3 for which a recent study reports yearly increases of around 2% in Europe and the U.S. and up to 6% in East Asia. Both species are currently actively monitored with several satellite sounders, which provide daily global measurements. Yet, the spatial resolution of current sounders is inadequate for resolving the highly heterogonous spatial distributions of both species. This is particularly the case for point source emitters, for which satellites are currently only able to quantify the largest and most isolated ones. To fill the important gap in the monitoring landscape, a satellite called Nitrosat has been proposed in answer to ESA’s Earth Explorer call. The satellite would allow making simultaneous measurements of NO2 and NH3 at a spatial resolution of 500 meter. In support to the Nitrosat proposal, ESA has funded a project called NITRO-CAM (Nitrogen cycle airborne measurements), which aims at mapping simultaneously NO2 and NH3 in the Greater Berlin area using aircraft measurements. It is the results of this campaign that are presented here. These can be seen as proof-of-concept for Nitrosat, but are also interesting in their own right. A larger focus is given to NH3, for which the presented measurements are the first of their kind.Campaign flights were performed in the surroundings of Berlin in the autumn of 2020. A follow-up campaign is foreseen in early spring. Measurements are performed with BIRA’s UV-VIS spectrometer newly-developed SWING instrument for NO2 and TELOPS thermal infrared HYPER-CAM for NH3. Surveying gapless areas of at least 10 by 10 km, the measurements enable capturing the emissions of both point and area sources, and are suitable for degrading at various hypothetical satellite instrument footprints. For NO2 specifically, Berlin and nearby power plants are targeted, while for NH3 the Piesteritz fertilizer factory is targeted, as well as rural areas in the surroundings of Berlin.

The nitrogen cycle has been heavily perturbed due to ever growing agriculture, industry, transport and domestic production. It is believed that we now have reached a point where the nitrogen biochemical flow has exceeded its planetary boundary for a safe operating zone. This goes together with a cascade of impacts on human health and ecosystems. To better understand and address these impacts, there is a critical need to quantify the global nitrogen cycle and monitor its perturbations on all scales, down to the urban or agricultural source.The Nitrosat concept, which was proposed most recently in the framework of ESA’s Earth Explorer 11 call, has for overarching objective to simultaneously identify the emission contributions of NH3 and NO2 from farming activities, industrial complexes, transport, fires and urban areas. The specific Nitrosat science goals are to:Quantify the emissions of NH3 and NO2 on the landscape scales, to expose individual sources and characterize the temporal patterns of their emissions. Quantify the relative contribution of agriculture, in its diversity of sectors and practices, to the total emissions of reactive nitrogen. Quantify the contribution of reactive nitrogen to air pollution and its impact on human health. Constrain the atmospheric dispersion and surface deposition of reactive nitrogen and its impacts on ecosystems and climate; and contribute to monitoring policy progress to reduce nitrogen deposition in Natura 2000 areas in Europe. Reduce uncertainties in the contribution of reactive nitrogen to climate forcing, atmospheric chemistry and interactions between biogeochemical cycles. To achieve these objectives, Nitrosat would consist of an infrared Imaging Fourier Transform Spectrometer and a Visible Imaging Pushbroom Spectrometer. These imaging spectrometers will measure NH3 and NO2 (respectively) at 500 m, which is the required spatial scale to differentiate, identify and quantify the main point and area sources in a single satellite overpass. Source regions would be probed from once a week to once a month to reveal the seasonal patterns. Combined with air quality models, assimilation and inverse modelling, these measurements would allow assessing the processes that are relevant for the human disruption of the nitrogen cycle and their resulting effects, in much more detail than what will be achieved with the satellite missions that are planned in the next decade. In this way, Nitrosat would enable informed evaluations of future policies on nitrogen emission control.

The Infrared Atmospheric Sounding Interferometer (IASI) mission consists of a suite of three infrared sounders providing today over 13 years of consistent global measurements (from end of 2007 up to now). In this work we use the recently developed version 3 of the IASI NH3 dataset to derive global, regional and national trends from 2008 to 2018. Reported national trends are analysed in the light of changing anthropogenic and pyrogenic NH3 emissions, meteorological conditions and the impact of sulphur and nitrogen oxides emissions. A case study is dedicated to the Netherlands. Temporal variation on shorter timescales will also be investigated.

The Syrian civil war started in 2011, with dramatic social, political, economic, and environmental consequences over the whole area of Syria and nearby countries. Agriculture, in particular, suffered massively. Several studies used satellite-retrieved data and imagery to examine the spatio-temporal changes in the region, due to the civil war. For instance, open-source satellite imagery could show the damage in urban areas, and provide an estimate of the number of people affected by the crisis.In this study, we investigate the impacts of the Syrian civil war on atmospheric ammonia (NH3) emitted from industrial and agricultural activities during the 2008-2019 period. Our analyses are based on the NH3 measurements from the IASI instruments onboard the Metop satellites. Firstly, land-use changes and a decrease in agricultural emissions are explored over the country. We also investigate the changes in atmospheric NH3 over an ammonia plant, which activities have been suspended due to several conflict-related events. We show that the NH3 columns retrieved from IASI are directly affected by the war, and those periods of intense conflict and siege are reflected in lower NH3 concentrations, which are not driven by meteorology. The interpretation of the identified changes in atmospheric NH3 is supported by the analyses of NO2 columns from GOME-2 as well as satellite imagery and land cover data. The latter is used to highlight the change in croplands’ area over the years, and the satellite images are used to show the activity of the ammonia plant.

Atmospheric ammonia (NH3) is a precursor to fine particulate matter and a source of nitrogen (N) deposition that can adversely affect ecosystem health. The main sources of NH3 – agriculture and biomass burning – are undergoing or expected to undergo substantial changes in Africa. Although evidence of increasing NH3 over parts of Africa has been observed, the mechanisms behind these trends are not well understood. Here we use observations of atmospheric NH3 vertical column densities (VCDs) from the Infrared Atmospheric Sounding Interferometer (IASI) along with other satellite observations of the land surface and atmosphere to evaluate how NH3 concentrations have changed over Africa from 2008 through 2017, and what has caused those changes. We find that NH3 VCDs have increased over several regions, including much of West Africa and parts of the Lake Victoria Basin. In West Africa NH3 VCDs are observed to increase during the late dry season, with increases of over 6 % yr−1 in Nigeria during February and March. These positive trends are associated with increasing burned area and CO trends during these months, likely related to agricultural preparation. Increases are also observed in the Lake Victoria Basin, where they are associated with expanding agricultural area. In contrast, South Sudan NH3 VCDs declined by over 2 % yr−1 during the February through May period, with the largest rates of change over the Sudd wetlands. Annual maxima in NH3 VCDs in South Sudan occur during February through May and are associated with drying of temporarily flooded wetland soils, which favor emissions of NH3. The change in mean NH3 VCDs over the Sudd and all of South Sudan during February through May is strongly correlated with variation in wetland extent in the Sudd: in years when more area remained flooded during the dry season, NH3 concentrations were higher (r = 0.69, p = 0.03). Relationships between agriculture and NH3 can be observed when evaluating national-scale statistics: countries with the largest declines in NH3 VCDs concentrations over time tended to have the smallest growth rates in crop productivity and livestock numbers as well as smaller negative changes in burned area than other countries. Fertilizer use in Africa is currently low but growing; implementing practices that can limit NH3 losses from fertilizer as agriculture is intensified may help mitigate impacts on health and ecosystems.

Ammonia (NH3) is a major source of nitrates in the atmosphere, and a major source of fine particulate matter. As such, there have been increasing efforts to measure the atmospheric abundance of NH3 and its spatial and temporal variability. In this study, long-term measurements of NH3 derived from multiscale datasets are examined. These NH3 datasets include 16 years of total column measurements using Fourier transform infrared (FTIR) spectroscopy, three years of surface in-situ measurements, and 10 years of total column measurements from the Infrared Atmospheric Sounding Interferometer (IASI). The datasets were used to quantify NH3 temporal variability over Toronto, Canada. The multiscale datasets were also compared to assess the observational footprint of the FTIR measurements. All three time series showed positive trends in NH3 over Toronto: 3.34 ± 0.46 %/year from 2002 to 2018 in the FTIR columns, 8.88 ± 2.83 %/year from 2013 to 2017 in the surface in-situ data, and 8.38 ± 0.77 %/year from 2008 to 2018 in the IASI columns. To assess the observational footprint of the FTIR NH3 columns, correlations between the datasets were examined. The best correlation between FTIR and IASI was obtained with coincidence criteria of ≤ 25 km and ≤ 20 minutes, with r = 0.73 and a slope of 1.14 ± 0.06. Additionally, FTIR column and in-situ measurements were standardized and correlated. Comparison of 24-day averages and monthly averages resulted in correlation coefficients of r = 0.72 and r = 0.75, respectively, although correlation without resampling to reduce high-frequency variability led to a poorer correlation, with r = 0.39. The GEOS-Chem model, run at 2° × 2.5° resolution, was compared against FTIR and IASI to assess model performance and investigate correlation of observational data and model output, both with local column measurements (FTIR) and measurements on a regional scale (IASI). Comparisons on a regional scale (a domain spanning 35° N to 53° N, and 93.75° W to 63.75° W) resulted in r = 0.57, and thus a coefficient of determination, which is indicative of the predictive capacity of the model, of r2 = 0.33, but comparing a single model grid point against the FTIR resulted in a poorer correlation, with r2 = 0.13, indicating that a finer spatial resolution is needed for modeling NH3.

Anthropogenic emissions of reactive nitrogen species have significantly increased, largely because of discharges from livestock, agricultural intensification and fertilizer use. Reactive nitrogen affects air quality, sensitive natural ecosystems, and the carbon balance. The proposed mission aims at providing high spatial resolution measurements (

Limited availability of atmospheric ammonia (NH3) observations, limits our understanding of controls on its spatial and temporal variability and its interactions with ecosystems. Here we used the Model for Ozone and Related chemical Tracers (MOZART-4) global chemistry transport model and the Hemispheric Transport of Air Pollution version-2 (HTAP-v2) emission inventory to simulate global NH3 distribution for the year 2010. We present a first comparison of the model with monthly averaged satellite distributions and limited ground-based observations available across South Asia. The MOZART-4 simulations over South Asia and East Asia are evaluated with the NH3 retrievals obtained from the Infrared Atmospheric Sounding Interferometer (IASI) satellite and 69 ground based monitoring stations for air quality across South Asia, and 32 ground based monitoring stations from the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) of China. We identify the northern region of India (Indo-Gangetic Plain, IGP) as a hotspot for NH3 in Asia, both using the model and satellite observations. In general, a close agreement was found between yearly-averaged NH3 total columns simulated by the model and IASI satellite measurements over the IGP, South Asia (r = 0.85) and North China Plain (NCP), of East Asia (r = 0.88). However, the MOZART-4 simulated NH3 column is substantially higher over South Asia than East Asia, as compared with the IASI retrievals, which show smaller differences. Model simulated surface NH3 concentrations indicate smaller concentrations in all seasons than surface NH3 measured by the ground based observations over South and East Asia, although uncertainties remain in the available surface NH3 measurements. Overall, the comparison of East Asia and South Asia using both MOZART-4 model and satellite observations showed smaller NH3 columns in East Asia compared with South Asia for comparable emissions, indicating rapid dissipation of NH3 due to secondary aerosol formation, which can be explained by larger emissions of acidic precursor gases in East Asia.

The global concentration of reactive nitrogen (e.g. NH3, NOx and N2O) has intensely increased since the pre-industrial era. Ammonia (NH3) is one of the main sources of reactive nitrogen in the atmosphere and plays a crucial role in the formation of inorganic particulate matter, which harms health and deteriorates air quality. In addition to that, the wet/dry deposition of ammonia derivatives affects ecosystems through acidification and eutrophication of soil and water bodies; leading to a loss in biodiversity and intensification of the response to climate change. NH3 is mainly emitted by biomass burning and agricultural activities. Agriculture contributes to air pollution and is affected by atmospheric composition, meteorology and climate change.Several studies proved the efficiency of the IASI instrument aboard Metop satellites in measuring ammonia from space. For the last ten years, hotspots of ammonia point sources have been identified and categorized around the world.In this poster, we explore the interaction of atmospheric ammonia with land, meteorological, and leaf conditions. We look at the temporal variability of ammonia in different regions of the world. The relationship land-ammonia volatilization is assessed by comparing the variability of surface soil moisture and the skin temperature products from the ECMWF latest reanalysis (ERA5) with IASI NH3 total columns. The meteorology-ammonia relation is examined, by looking at air temperature, humidity, precipitation, planetary boundary layer height, and wind speed/direction. Agricultural seasons in studied regions are detected from space in matter of leaf area per ground area. The crop-ammonia relation is assessed by looking at the Leaf Area Index (LAI) products. The regions examined have been identified as point sources and/or hotspots of ammonia of agricultural and industrial sources (mainly fertilizer industry).The result of this work will improve our understanding of biosphere-atmosphere interactions, in particular, the relationship between ammonia on the one hand and land, meteorology and crops on the other hand, in different regions in the world.

Air pollution is one of the leading global causes of premature mortality, necessitating routine monitoring of air quality in cities where most (55%) people now reside. Surface monitors are sparse and costly to operate, whereas satellites provide global coverage of a multitude of pollutants spanning more than 2 decades. Here we make use of the dynamic range of satellite products to understand long-term changes in air quality in target cities in the UK (London and Birmingham) and India (Kanpur and Delhi). These include nitrogen dioxide (NO2) from OMI for 2005-2018, formaldehyde (HCHO) from OMI for 2005-2016 to monitor non-methane volatile organic compounds (NMVOCs), ammonia (NH3) from IASI for 2008-2017 and aerosol optical depth (AOD) from MODIS for 2005-2018 to monitor PM2.5. Where surface observations are available (almost exclusively the UK), we first evaluate the ability of the satellite observations to reproduce variability in surface air pollution. We find temporal consistency for most pollutants (R >= 0.5), with the exception of MODIS AOD and surface PM2.5 (R = 0.3), but the decline in AOD (3.0% a-1) and surface PM2.5 (2.8% a-1), so far only evaluated for London, is similar. Inconsistencies result from seasonal variability in the planetary boundary layer, differences in sampling footprint between the satellite and surface monitors, and interferences in the surface measurements (as is the case for NO2). We find a decrease in all pollutants in Birmingham and London and an increase in all pollutants in Delhi and Kanpur, over the analysis period, but not all trends are significant. Birmingham and London NO2 both declined by 2.5% a-1, whereas Delhi NO2 increased by 2.0% a-1, so that by the end of 2018 Delhi and London have the same tropospheric column concentrations of NO2. Only Delhi exhibits a significant NMVOCs trend (increase) of 1.8% a-1. NH3 trends are not significant in any of the four cities, consistent with bottom-up inventories and lack of direct controls on emissions of this pollutant, mostly from agriculture. These data show no evidence of air quality improvements in Delhi, despite rollout of strict controls on industry and vehicles.

Ammonia (NH3) is a key precursor to fine particulate matter (PM2.5) and has remarkable impacts on air quality, climate, and ecosystem diversity. Satellite NH3 observations from the Infrared Atmospheric Sounding Interferometer (IASI) provide long-term measurements of ammonia globally since 2007 and have been validated by both ground based and airborne measurements. In this study, IASI Level 2 NH3 columns were oversampled at high-resolution (0.02°×0.02°) from 2008 to 2017 to yield monthly NH3 maps covering the two top agricultural exporting regions in the world, the contiguous U.S. (CONUS) and Europe. K-means clustering was applied to identify NH3 seasonality observations. The U.S. and Europe showed large temporal variabilities that differed by region and agricultural activities. For example, in the U.S., areas dominated by livestock waste emissions had peak NH3 column abundances in the summer, while cropland-dominated regions tended to have spring peak and sometimes a fall shoulder. We also compared IASI NH3 column amounts to NH3 surface concentrations provided by the Ammonia Monitoring Network (AMoN) in the CONUS. Since IASI provides column NH3 at ~ 9:30 LST while AMoN provides biweekly averaged surface NH3, different factors were examined to find out the most important factors for the comparison between the two datasets (spatial window, temporal coverage, data averaging). We found that IASI data temporal coverage of the 2-week AMoN sampling period was the key factor in improving correlations. The r value increased from 0.38 to 0.73 when at least 80% of the two-week AMoN period had concurrent satellite measurements within a 25 km radius of the site. Neglecting interannual variability, the r value of multiyear monthly averaged AMoN and IASI NH3 is 0.68, indicating the importance of temporal averaging. The good agreement between AMoN and IASI NH3 concentrations demonstrates the feasibility of utilizing satellite NH3 retrievals to better understand NH3 variability in these agricultural intensive regions. With the global coverage and long data record, satellite measurements are likely to be a cost-effective approach as a supplemental source of information for understanding NH3 variability, as well as guiding the locations of future sites within ground monitoring network. Finally, IASI NH3 spatiotemporal variabilities will be compared to AM3 model output with bottom-up emission inventory (Magnitude And Seasonality of Agricultural Emissions model for NH3, MASAGE_NH3).

Atmospheric ammonia (NH3) plays an important role in the formation of fine particulate matter, leading to severe environmental degradation and human health issues. In this work, ground-based FTIR observations are used to obtain the total columns and vertical profiles of atmospheric NH3 at a measurement site in Hefei, China, from December 2016 to November 2018. The spatial distribution and temporal variation, seasonal trend, emission sources and potential sources of NH3 are analyzed. The time series of ammonia columns show that FTIR observations captured the seasonal cycle of NH3 over the two years of measurement, with a 22.14 % yr-1 annual increase rate over the Hefei site. We used IASI satellite data to compare with the FTIR data, and the correlation coefficients (R) between the two datasets are 0.86 and 0.78 for IASI-A and IASI-B, respectively. The results demonstrate the IASI data are in broad agreement with our FTIR data. To examine the contribution of traffic to NH3 columns, we analyze the relationship of NH3 columns with CO surface concentrations. NH3 columns show high correlation (R = 0.77) with CO concentrations in summer, indicating that the elevated NH3 columns are partly caused by urban emissions from vehicles. Further, high correlation of NH3 columns with air temperature is obvious from their diurnal variation during the observation period. In addition, the clear correlation between NH3 columns and air temperature in spring and autumn over Hefei, suggests that agriculture was indeed the main source of ammonia in spring and autumn. Furthermore, the back trajectories of air masses calculated by the HYSPLIT model confirmed that agriculture was the dominant source of ammonia in spring, autumn and winter, while urban anthropogenic emissions contributed to the high level of NH3 in summer over the Hefei site. The potential source areas influencing the NH3 columns were distributed in the local area of Hefei, the northern part of Anhui province, as well as Shangdong, Jiangsu and Henan provinces. This study helps to identify the emission sources and potential sources that contribute to NH3 columns over Hefei, a highly populated and polluted area. This is the first time that ground-based FTIR remote sensing of NH3 columns and comparison with satellite data are reported in China.