We use in situ observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring Project, 11 surface site campaigns as well as Infrared ...Atmospheric Sounding Interferometer (IASI) satellite measurements with the GEOS-Chem model to investigate inorganic aerosol loading and atmospheric ammonia concentrations over the United States. IASI observations suggest that current ammonia emissions are underestimated in California and in the springtime in the Midwest. In California this underestimate likely drives the underestimate in nitrate formation in the GEOS-Chem model. However in the remaining continental United States we find that the nitrate simulation is biased high (normalized mean bias > = 1.0) year-round, except in Spring (due to the underestimate in ammonia in this season). None of the uncertainties in precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concentrations, the reaction rate for the formation of nitric acid, or the dry deposition velocity of nitric acid are able to explain this bias. We find that reducing nitric acid concentrations to 75% of their simulated values corrects the bias in nitrate (as well as ammonium) in the US. However the mechanism for this potential reduction is unclear and may be a combination of errors in chemistry, deposition and sub-grid near-surface gradients. This "updated" simulation reproduces PM and ammonia loading and captures the strong seasonal and spatial gradients in gas-particle partitioning across the United States. We estimate that nitrogen makes up 15−35% of inorganic fine PM mass over the US, and that this fraction is likely to increase in the coming decade, both with decreases in sulfur emissions and increases in ammonia emissions.
Ammonia (NH3) emissions in the atmosphere have increased substantially over the past decades, largely because of intensive livestock production and use of fertilizers. As a short-lived species, NH3 ...is highly variable in the atmosphere and its concentration is generally small, except near local sources. While ground-based measurements are possible, they are challenging and sparse. Advanced infrared sounders in orbit have recently demonstrated their capability to measure NH3, offering a new tool to refine global and regional budgets. In this paper we describe an improved retrieval scheme of NH3 total columns from the measurements of the Infrared Atmospheric Sounding Interferometer (IASI). It exploits the hyperspectral character of this instrument by using an extended spectral range (800–1200 cm−1) where NH3 is optically active. This scheme consists of the calculation of a dimensionless spectral index from the IASI level1C radiances, which is subsequently converted to a total NH3 column using look-up tables built from forward radiative transfer model simulations. We show how to retrieve the NH3 total columns from IASI quasi-globally and twice daily above both land and sea without large computational resources and with an improved detection limit. The retrieval also includes error characterization of the retrieved columns. Five years of IASI measurements (1 November 2007 to 31 October 2012) have been processed to acquire the first global and multiple-year data set of NH3 total columns, which are evaluated and compared to similar products from other retrieval methods. Spatial distributions from the five years data set are provided and analyzed at global and regional scales. In particular, we show the ability of this method to identify smaller emission sources than those previously reported, as well as transport patterns over the ocean. The five-year time series is further examined in terms of seasonality and interannual variability (in particular as a function of fire activity) separately for the Northern and Southern Hemispheres.
Atmospheric carbon monoxide (CO) distributions are controlled by anthropogenic emissions, biomass burning, transport and oxidation by reaction with the hydroxyl radical (OH). Quantifying trends in CO ...is therefore important for understanding changes related to all of these contributions. Here we present a comprehensive record of satellite observations from 2000 through 2011 of total column CO using the available measurements from nadir-viewing thermal infrared instruments: MOPITT, AIRS, TES and IASI. We examine trends for CO in the Northern and Southern Hemispheres along with regional trends for Eastern China, Eastern USA, Europe and India. We find that all the satellite observations are consistent with a modest decreasing trend similar to -1 % yr super(-1) in total column CO over the Northern Hemisphere for this time period and a less significant, but still decreasing trend in the Southern Hemisphere. Although decreasing trends in the United States and Europe have been observed from surface CO measurements, we also find a decrease in CO over E. China that, to our knowledge, has not been reported previously. Some of the interannual variability in the observations can be explained by global fire emissions, but the overall decrease needs further study to understand the implications for changes in anthropogenic emissions.
Atmospheric aerosols impact air quality and global climate. Space based measurements are the best way to observe their spatial and temporal distributions, and can also be used to gain better ...understanding of their chemical, physical and optical properties. Aerosol composition is the key parameter affecting the refractive index, which determines how much radiation is scattered and absorbed. Composition of aerosols is unfortunately not measured by state of the art satellite remote sounders. Here we use high resolution infrared measurements for aerosol type differentiation, exploiting, in that part of spectrum, the dependency of their refractive index on wavelength. We review existing detection methods and present a unified detection method based on linear discrimination analysis. We demonstrate this method on measurements of the Infrared Atmospheric Sounding Interferometer (IASI) and five different aerosol types, namely volcanic ash, windblown sand, sulfuric acid droplets, ammonium sulfate and smoke particles. We compare these with traditional MODIS AOD measurements. The detection of the last three types is unprecedented in the infrared in nadir mode, but is very promising, especially for sulfuric acid droplets which are detected in the lower troposphere and up to 6 months after injection in the upper troposphere/lower stratosphere.
Sulphur dioxide (SO2 ) fluxes of active degassing volcanoes are routinely measured with ground-based equipment to characterize and monitor volcanic activity. SO2 of unmonitored volcanoes or from ...explosive volcanic eruptions, can be measured with satellites. However, remote-sensing methods based on absorption spectroscopy generally provide integrated amounts of already dispersed plumes of SO2 and satellite derived flux estimates are rarely reported. Here we review a number of different techniques to derive volcanic SO2 fluxes using satellite measurements of plumes of SO2 and investigate the temporal evolution of the total emissions of SO2 for three very different volcanic events in 2011: Puyehue-Cordón Caulle (Chile), Nyamulagira (DR Congo) and Nabro (Eritrea). High spectral resolution satellite instruments operating both in the ultraviolet-visible (OMI/Aura and GOME-2/MetOp-A) and thermal infrared (IASI/MetOp-A) spectral ranges, and multispectral satellite instruments operating in the thermal infrared (MODIS/Terra-Aqua) are used. We show that satellite data can provide fluxes with a sampling of a day or less (few hours in the best case). Generally the flux results from the different methods are consistent, and we discuss the advantages and weaknesses of each technique. Although the primary objective of this study is the calculation of SO2 fluxes, it also enables us to assess the consistency of the SO2 products from the different sensors used.
In this paper, we describe a new flexible and robust NH3 retrieval algorithm from measurements of the Infrared Atmospheric Sounding Interferometer (IASI). The method is based on the calculation of a ...spectral hyperspectral range index (HRI) and subsequent conversion to NH3 columns via a neural network. It is an extension of the method presented in Van Damme et al. (2014a) who used lookup tables (LUT) for the radiance‐concentration conversion. The new method inherits the advantages of the LUT‐based method while providing several significant improvements. These include the following: (1) Complete temperature and humidity vertical profiles can be accounted for. (2) Third‐party NH3 vertical profile information can be used. (3) Reported positive biases of LUT retrieval are reduced, and finally (4) a full measurement uncertainty characterization is provided. A running theme in this study, related to item (2), is the importance of the assumed vertical NH3 profile. We demonstrate the advantages of allowing variable profile shapes in the retrieval. As an example, we analyze how the retrievals change when all NH3 is assumed to be confined to the boundary layer. We analyze different averaging procedures in use for NH3 in the literature, introduced to cope with the variable measurement sensitivity and derive global averaged distributions for the year 2013. A comparison with a GEOS‐Chem modeled global distribution is also presented, showing a general good correspondence (within ±3 × 1015 molecules.cm−2) over most of the Northern Hemisphere. However, IASI finds mean columns about 1–1.5 × 1016 molecules.cm−2 (∼50–60%) lower than GEOS‐Chem for India and the North China plain.
Key Points
New IASI‐NH3 retrieval approach based on a neural network
Flexible NH3 vertical profiles ease comparison with model and in situ data
The impact of using ECMWF or GEOS‐Chem vertical profile information leads to differences in the retrieved columns up to 50‐60%
As one of the most abundant oxygenated volatile organic compounds in the atmosphere, acetone (CH3COCH3) influences atmospheric oxidants levels and ozone formation. Here we report the first ...unambiguous identification of acetone from the nadir‐viewing satellite sounder Infrared Atmospheric Sounding Interferometer (IASI). Via a neural network‐based retrieval approach that was previously applied to the retrieval of other weak absorbers, we obtain daily global acetone retrievals. A first intercomparison with independent measurements is conducted. As the retrieval method is computationally fast, it allowed the full reprocessing of the 2007–2018 IASI time series. Analysis of the retrieved global product and its seasonality suggests that emissions of acetone and precursors from the terrestrial biosphere at Northern Hemisphere middle and high latitudes are the main contributors to the atmospheric acetone abundance, more than year‐round oxidation of anthropogenic isoalkanes. Remarkably, biomass burning does not appear to be a strong global source of acetone.
Plain Language Summary
Acetone is an omnipresent atmospheric gas that has a significant impact on atmospheric chemistry, especially on the concentration of other species that can degrade greenhouse gasses like methane. However, its sources remain uncertain and poorly quantified, in part due to the absence of routine measurements. Here we show that acetone can be detected from space by the Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop satellites. From the IASI measurements, we produce the first daily distributions of acetone abundance at the global scale, using a neural network algorithm. Comparison with acetone measurements made in various aircraft campaigns shows a good agreement. From the analysis of the IASI acetone distribution and variability, we deduce that the dominant source of atmospheric acetone is the terrestrial vegetation at Northern Hemisphere middle and high latitudes. Human activities also contribute to the atmospheric acetone concentrations, although fires do not appear as a strong source globally.
Key Points
The atmospheric acetone spectral signature can be unambiguously observed in IASI/Metop satellite infrared spectra
First daily global distributions of acetone columns are produced using a neural network‐based retrieval approach
Northern Hemisphere biogenic emissions appear as the main acetone source, more than anthropogenic isoalkanes and biomass burning
Assessments of carbon monoxide emissions through inverse modeling are dependent on the modeled abundance of the hydroxyl radical (OH) which controls both the primary sink of CO and its photochemical ...source through hydrocarbon oxidation. However, most chemistry transport models (CTMs) fall short of reproducing constraints on hemispherically averaged OH levels derived from methylchloroform (MCF) observations. Here we construct five different OH fields compatible with MCF‐based analyses, and we prescribe those fields in a global CTM to infer CO fluxes based on Infrared Atmospheric Sounding Interferometer (IASI) CO columns. Each OH field leads to a different set of optimized emissions. Comparisons with independent data (surface, ground‐based remotely sensed, aircraft) indicate that the inversion adopting the lowest average OH level in the Northern Hemisphere (7.8 × 105 molec cm−3, ∼18% lower than the best estimate based on MCF measurements) provides the best overall agreement with all tested observation data sets.
Plain Language Summary
Satellite measurements of a pollutant can be used to deduce the emissions of this pollutant to the atmosphere. But often, such estimates have errors due to our uncertain knowledge of the chemical lifetime of pollutants. Here we assess the importance of specifying the correct lifetime for deducing the sources of carbon monoxide. We also show that the measurements can provide new constraints on the lifetime of pollutants. More precisely, we provide constraints on the abundance of OH radicals, often considered to be the main detergent of the atmosphere. Indeed, OH radical is the main oxidant of carbon monoxide, but also methane, which is a potent greenhouse gas.
Key Points
The global CO sources were inferred based on IASI CO columns, using a global CTM and prescribed OH fields
Varying hemispheric mean OH levels within their uncertainties estimated from methylchloroform analyses has a strong impact on derived fluxes
The inversion adopting the lowest OH in NH provides the best match with satellite, in situ, and FTIR data
This work presents observations of a series of short-lived species in biomass burning plumes from the Infrared Atmospheric Sounding Interferometer (IASI), launched onboard the MetOp-A platform in ...October 2006. The strong fires that have occurred in the Mediterranean Basin – and particularly Greece – in August 2007, and those in Southern Siberia and Eastern Mongolia in the early spring of 2008 are selected to support the analyses. We show that the IASI infrared spectra in these fire plumes contain distinctive signatures of ammonia (NH3), ethene (C2H4), methanol (CH3OH) and formic acid (HCOOH) in the atmospheric window between 800 and 1200 cm−1, with some noticeable differences between the plumes. Peroxyacetyl nitrate (CH3COOONO2, abbreviated as PAN) was also observed with good confidence in some plumes and a tentative assignment of a broadband absorption spectral feature to acetic acid (CH3COOH) is made. For several of these species these are the first reported measurements made from space in nadir geometry. The IASI measurements are analyzed for plume height and concentration distributions of NH3, C2H4 and CH3OH. The Greek fires are studied in greater detail for the days associated with the largest emissions. In addition to providing information on the spatial extent of the plume, the IASI retrievals allow an estimate of the total mass emissions for NH3, C2H4 and CH3OH. Enhancement ratios are calculated for the latter relative to carbon monoxide (CO), giving insight in the chemical processes occurring during the transport, the first day after the emission.
Thermal infrared sounding of sulphur dioxide (SO2) from space has gained appreciation as a valuable complement to ultraviolet sounding. There are several strong absorption bands of SO2 in the ...infrared, and atmospheric sounders, such as AIRS (Atmospheric Infrared Sounder), TES (Tropospheric Emission Spectrometer) and IASI (Infrared Atmospheric Sounding Interferometer) have the ability to globally monitor SO2 abundances. Most of the observed SO2 is found in volcanic plumes. In this paper we outline a novel algorithm for the sounding of SO2 above ~5 km altitude using high resolution infrared sounders and apply it to measurements of IASI. The main features of the algorithm are a wide applicable total column range (over 4 orders of magnitude, from 0.5 to 5000 dobson units), a low theoretical uncertainty (3–5%) and near real time applicability. We make an error analysis and demonstrate the algorithm on the recent eruptions of Sarychev, Kasatochi, Grimsvötn, Puyehue-Cordón Caulle and Nabro.
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