• Retrievals of far infrared surface emissivity are reported for the first time, exploiting aircraft observations taken over Greenland. • The retrieved emissivity reaches values as low as 0.89 over the range 360-535 cm-1 , where the associated uncertainties are smallest. • Simulations of the surface emissivity are unable to simultaneously match retrievals in the far and mid infrared.

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Abstract. The direct radiative effect (DRE) of aerosols, which is the instantaneous radiative impact of all atmospheric particles on the Earth's energy balance, is sometimes confused with the direct radiative forcing (DRF), which is the change in DRE from pre-industrial to present-day (not including climate feedbacks). In this study we couple a global chemical transport model (GEOS-Chem) with a radiative transfer model (RRTMG) to contrast these concepts. We estimate a global mean all-sky aerosol DRF of −0.36 Wm −2 and a DRE of −1.83 Wm −2 for 2010. Therefore, natural sources of aerosol (here including fire) affect the global energy balance over four times more than do present-day anthropogenic aerosols. If global anthropogenic emissions of aerosols and their precursors continue to decline as projected in recent scenarios due to effective pollution emission controls, the DRF will shrink (−0.22 Wm −2 for 2100). Secondary metrics, like DRE, that quantify temporal changes in both natural and anthropogenic aerosol burdens are therefore needed to quantify the total effect of aerosols on climate.

Many clouds important to the Earth's energy balance contain small amounts of liquid water, yet despite many improvements, large differences in retrievals of their liquid water amount and particle size still must be resolved.

[1] Ammonia (NH 3 ) has significant impacts on biodiversity, eutrophication, and acidification. Widespread uncertainty in the magnitude and seasonality of NH 3 emissions hinders efforts to address these issues. In this work, we constrain U.S. NH 3 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 NH 3 and wet deposited NH x 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 NH 3 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 NH 3 sources may be necessary to enhance year-round model performance across the full range of gas and aerosol evaluations.

Abstract. Presently only limited sets of tropospheric ammonia (NH 3 ) measurements in the Earth's atmosphere have been reported from satellite and surface station measurements, despite the well-documented negative impact of NH 3 on the environment and human health. Presented here is a detailed description of the satellite retrieval strategy and analysis for the Tropospheric Emission Spectrometer (TES) using simulations and measurements. These results show that: (i) the level of detectability for a representative boundary layer TES NH 3 mixing ratio value is ∼0.4 ppbv, which typically corresponds to a profile that contains a maximum level value of ∼1 ppbv; (ii) TES NH 3 retrievals generally provide at most one degree of freedom for signal (DOFS), with peak sensitivity between 700 and 900 mbar; (iii) TES NH 3 retrievals show significant spatial and seasonal variability of NH 3 globally; (iv) initial comparisons of TES observations with GEOS-CHEM estimates show TES values being higher overall. Important differences and similarities between modeled and observed seasonal and spatial trends are noted, with discrepancies indicating areas where the timing and magnitude of modeled NH 3 emissions from agricultural sources, and to lesser extent biomass burning sources, need further study.

[1] Atmospheric ammonia (NH 3 ) has recently been observed with infrared sounders from space. Here we present 1 year of detailed bidaily satellite retrievals with the Infrared Atmospheric Sounding Interferometer and some retrievals of the Tropospheric Emission Spectrometer over the San Joaquin Valley, California, a highly polluted agricultural production region. Several sensitivity issues are discussed related to the sounding of ammonia, in terms of degrees of freedom, averaging kernels, and altitude of maximum sensitivity and in relation to thermal contrast and concentration. We also discuss their seasonal dependence and sources of errors. We demonstrate boundary layer sensitivity of infrared sounders when there is a large thermal contrast between the surface and the bottom of the atmosphere. For the San Joaquin Valley, large thermal contrast is the case for daytime measurements in spring, summer, and autumn and for nighttime measurements in autumn and winter when a large negative thermal contrast is amplified by temperature inversion.

Abstract.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 Crosstrack 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 NH 3 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.