Observations of atmospheric ammonia are important in understanding and modelling the impact of ammonia on both human health and the natural environment. We present a detailed description of a robust ...retrieval algorithm that demonstrates the capabilities of utilizing Cross-track Infrared Sounder (CrIS) satellite observations to globally retrieval ammonia concentrations. Initial ammonia retrieval results using both simulated and real observations show that (i) CrIS is sensitive to ammonia in the boundary layer with peak vertical sensitivity typically around ~ 850–750 hPa (~ 1.5 to 2.5 km), which can dip down close to the surface (~ 900 hPa) under ideal conditions, (ii) it has a minimum detection limit of ~ 1 ppbv (peak profile value typically at the surface), and (iii) the information content can vary significantly with maximum values of ~ 1 degree-of-freedom for signal. Comparisons of the retrieval with simulated "true" profiles show a small positive retrieval bias of 6% with a standard deviation of ~ ± 20% (ranging from ± 12 to ± 30% over the vertical profile). Note that these uncertainty estimates are considered as lower bound values as no potential systematic errors are included in the simulations. The CrIS NH3 retrieval applied over the Central Valley in CA, USA, demonstrates that CrIS correlates well with the spatial variability of the boundary layer ammonia concentrations seen by the nearby Quantum Cascade-Laser (QCL) in situ surface and the Tropospheric Emission Spectrometer (TES) satellite observations as part of the DISCOVER-AQ campaign. The CrIS and TES ammonia observations show quantitatively similar retrieved boundary layer values that are often within the uncertainty of the two observations. Also demonstrated is CrIS's ability to capture the expected spatial distribution in the ammonia concentrations, from elevated values in the Central Valley from anthropogenic agriculture emissions, to much lower values in the unpolluted or clean surrounding mountainous regions. These initial results demonstrate the capabilities of the CrIS satellite to measure ammonia.
Formic acid (HCOOH) is one of the most abundant carboxylic acids and a dominant source of atmospheric acidity. Recent work indicates a major gap in the HCOOH budget, with atmospheric concentrations ...much larger than expected from known sources. Here, we employ recent space-based observations from the Tropospheric Emission Spectrometer with the GEOS-Chem atmospheric model to better quantify the HCOOH source from biomass burning, and assess whether fire emissions can help close the large budget gap for this species. The space-based data reveal a severe model HCOOH underestimate most prominent over tropical burning regions, suggesting a major missing source of organic acids from fires. We develop an approach for inferring the fractional fire contribution to ambient HCOOH and find, based on measurements over Africa, that pyrogenic HCOOH:CO enhancement ratios are much higher than expected from direct emissions alone, revealing substantial secondary organic acid production in fire plumes. Current models strongly underestimate (by 10 ± 5 times) the total primary and secondary HCOOH source from African fires. If a 10-fold bias were to extend to fires in other regions, biomass burning could produce 14 Tg/a of HCOOH in the tropics or 16 Tg/a worldwide. However, even such an increase would only represent 15–20% of the total required HCOOH source, implying the existence of other larger missing sources.
Reactive nitrogen (Nr) is an essential nutrient to plants and a limiting element for growth in many ecosystems, but it can have harmful effects on ecosystems when in excess. Satellite‐derived surface ...observations are used together with a dry deposition model to estimate the dry deposition flux of the most abundant short‐lived nitrogen species, NH3 and NO2, over North America during the 2013 warm season. These fluxes demonstrate that the NH3 contribution dominates over NO2 for most regions (comprising ~85% of their sum in Canada and ~65% in the U.S.), with some regional exceptions (e.g. Alberta and northeastern U.S.). Nationwide, ~51 t of N from these species were dry deposited in the U.S., approximately double the ~28 t in Canada over this period. Forest fires are shown to be the major contributor of dry deposition of Nr from NH3 in northern latitudes, leading to deposition fluxes 2–3 times greater than from expected amounts without fires.
Key Points
First use of satellite observations to estimate the dry deposition of reactive nitrogen (Nr) from ammonia (NH3)
Satellite estimates of NH3 and NO2 dry deposition indicate that the NH3 dominates over most regions across the North America during the 2013 warm season
Locations at northern latitudes affected by forest fires tend to have 2–3 times more dry deposition of ammonia relative to the local background
Ammonia (NH3) has significant impacts on biodiversity, eutrophication, and acidification. Widespread uncertainty in the magnitude and seasonality of NH3 emissions hinders efforts to address these ...issues. In this work, we constrain U.S. NH3 sources using observations from the TES satellite instrument with the GEOS‐Chem model and its adjoint. The inversion framework is first validated using simulated observations. We then assimilate TES observations for April, July, and October of 2006 through 2009. The adjoint‐based inversion allows emissions to be adjusted heterogeneously; they are found to increase in California throughout the year, increase in different regions of the West depending upon season, and exhibit smaller increases and occasional decreases in the Eastern U.S. Evaluations of the inversion using independent surface measurements show reduced model underestimates of surface NH3 and wet deposited NHx in April and October; however, the constrained simulation in July leads to overestimates of these quantities, while TES observations are still under predicted. Modeled sulfate and nitrate aerosols concentrations do not change significantly, and persistent nitrate overestimation is noted, consistent with previous studies. Overall, while satellite‐based constraints on NH3 emissions improve model simulations in several aspects, additional assessment at higher horizontal resolution of spatial sampling bias, nitric acid formation, and diurnal variability and bi‐directionality of NH3 sources may be necessary to enhance year‐round model performance across the full range of gas and aerosol evaluations.
Key PointsInverse modeling with TES satellite data helps constrain ammonia emissionsImprovements beyond NH3 sources are needed for better ammonium aerosol modelingNH3 emissions may be broadly underestimated throughout the U.S
•The MT_CKD water vapor continuum model is now a component of HITRAN.•The formulation for the temperature dependence of the water vapor self continuum is now a power law.•The MT_CKD water vapor ...continuum model has been modified in near-infrared windows and the far-infrared to better agree with measurements.•There is a need for additional experimental studies of water vapor continuum absorption.
Atmospheric radiative transfer calculations require information about the spectral absorption properties of all relevant gases in the atmospheric path. For years, much of the atmospheric community has relied on the HITRAN molecular spectroscopic database for absorption line information and the MT_CKD (Mlawer-Tobin_Clough-Kneizys-Davies) water vapor continuum model to specify water vapor continuum absorption. This paper reports on efforts related to the recent inclusion of the MT_CKD water vapor continuum model as a component of HITRAN. Details are provided about the restructuring of the MT_CKD model to separate its code and data and simplify the code structure. We also describe the reformulation of the temperature dependence of the water vapor self continuum in MT_CKD, motivated both by improvements to the model's accuracy at high temperatures and greater consistency with HITRAN. We also briefly describe other recent updates to the MT_CKD water vapor continuum. Finally, perspective is provided on the need for future water vapor continuum measurements.
The code and data for the MT_CKD water vapor continuum are available through the HITRAN website at https://hitran.org/mtckd and at the AER GitHub site at https://github.com/AER-RC/MT_CKD_H2O.
Air-broadened half-widths of the 22- and 183-GHz water-vapor lines and associated uncertainties have been determined using comparisons between ground-based radiometric measurements from Atmospheric ...Radiation Measurement sites in Oklahoma and Alaska, and MonoRTM, a radiative transfer model. Values of the widths obtained using the measurements are 0.0900 cm -1 /atm with 1.6% uncertainty for the 22-GHz line and 0.0992 cm -1 /atm with 2.4% uncertainty for the 183-GHz line. Also presented are spectroscopic parameters for these lines from new calculations performed using the complex implementation of the Robert-Bonamy theory (CRB). The CRB values of the air-broadened widths are 0.0913 cm -1 /atm with 3% uncertainty and a temperature exponent of 0.755 for the 22-GHz line and 0.0997 cm -1 /atm with 3% uncertainty and a temperature exponent of 0.769 for the 183-GHz line. The values for the air-broadened half-widths derived from the measurement/model comparisons show good agreement with the new CRB calculations. For future versions of MonoRTM, width values of 0.0900 and 0.0997 cm -1 /atm are to be adopted with temperature dependences of 0.76 and 0.77 for the 22- and 183-GHz lines, respectively.
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