Gas‐aerosol partitioning of ammonia in biomass burning plumes: Implications for the interpretation of spaceborne observations of ammonia and the radiative forcing of ammonium nitrate

Abstract

Satellite‐derived enhancement ratios of NH3 relative to CO column burden ( normalERNH3/CO) in fires over Alaska, the Amazon, and South Equatorial Africa are 35, 45, and 70% lower than the corresponding ratio of their emissions factors ( normalEFNH3/CO) from biomass burning derived from in situ observations. Simulations performed using the Geophysical Fluid Dynamics Laboratory AM3 global chemistry‐climate model show that these regional differences may not entirely stem from an overestimate of NH3 emissions but rather from changes in the gas‐aerosol partitioning of NH3 to NH4+. Differences between normalERNH3/CO and normalEFNH3/CO are largest in regions where normalEFNOx/NH3 is high, consistent with the production of NH4NO3. Biomass burning is estimated to contribute 11–23% of the global burden and direct radiative effect (DRE) of NH4NO3 (−15 to −28 mW m−2), despite accounting for less than 6% of the global source of NH3. Production of NH4NO3 is largely concentrated over the Amazon and South Equatorial Africa, where its DRE can reach −1.9 W m−2 during the biomass burning season.

On the Role of the Flaming to Smoldering Transition in the Seasonal Cycle of African Fire Emissions

“…The underestimation of CO columns exceeds the interannual variation in MOPITT observations, a feature that was also seen in other studies that used different atmospheric transport models and previous versions of the GFED data (Edwards et al, 2006;van Leeuwen et al, 2013). Additionally, the models driven by GFED cannot reproduce the late peak of satellite retrievals of NH 3 columns (Paulot et al, 2017) Compared to bottom-up emission estimates, the late peak of the inversion emissions has also been observed by studies that assimilated previous releases of MOPITT or Infrared Atmospheric Sounding Interferometer (IASI) retrievals in different data assimilation systems Chevallier et al, 2009;Pétron et al, 2004;Whitburn et al, 2015). We interpret the consistency with other inversion studies as a sign of robustness of the delayed timing in CO emissions retrieved in this study, when compared to both GFED and GFAS.…”

“…The underestimation of CO columns exceeds the interannual variation in MOPITT observations, a feature that was also seen in other studies that used different atmospheric transport models and previous versions of the GFED data (Edwards et al, ; van Leeuwen et al, ). Additionally, the models driven by GFED cannot reproduce the late peak of satellite retrievals of NH 3 columns (Paulot et al, ) and aerosol optical depth (AOD; Horowitz et al, ; Magi et al, ; Tummon et al, ) over Africa. These tracers follow different chemical processes than CO and have shorter atmospheric lifetimes; therefore, the modeling biases are probably caused by the underestimated emissions of GFED in the late season rather than by modeling deficiencies.…”

Revisiting the Impact of Sea Salt on Climate Sensitivity

“…− T (Dir. Aerosol) is estimated by calling the radiative transfer scheme in the absence of aerosol at each time step (Paulot et al, 2017). Similarly, − T (LW (clr)) and the longwave cloud feedback are estimated by calling the radiative transfer scheme in the absence of clouds at each time step.…”

Importance of Ammonia Gas-Particle Conversion Ratio in Haze Formation in the Rural Agricultural Environment

“…These findings collectively imply that the fundamental role of NH3 in regulating aerosol acidity is 46 still ambiguous, thus altering the SNA formation mechanism (Seinfeld and Pandis, 2012). 47 NH3 emission sources include agricultural practices, on-road vehicles (Chang et al, 2016;Sun et al, 2016) and 48 biomass burning (Lamarque et al, 2010;Paulot et al, 2017). Recent field measurements and modeling works reveal 49 that agricultural practices (i.e., animal manure and fertilizer application) contribute to 80-90% of total NH3 50 emissions in China Kang et al, 2016;Huang et al, 2011).…”