Inconsistency of ammonium–sulfate aerosol ratios with thermodynamic models in the eastern US: a possible role of organic aerosol
We identify a fundamental discrepancy between thermodynamic equilibrium theory and observations of inorganic aerosol composition in the eastern US in summer that shows low ammonium sulfate aerosol ratios. In addition, from 2003 to 2013, while SO2 emissions have declined due to US emission controls, aerosols have become more acidic in the southeastern US. To explain these observations, we suggest that the large and increasing source of organic aerosol may be affecting thermodynamic equilibrium.
For more: Silvern et al., 2017
Observed NO/NO2 ratios in the upper troposphere imply errors in NO-NO2-O3 cycling kinetics or an unaccounted NOx reservoir
We identify large discrepancies between observed NO/NO2 ratios and models representing our best understanding of the chemistry controlling NO and NO2 in the upper troposphere over the southeast United States during August–September 2013. We suggest that either unrecognized chemistry or errors in modeled cycling between NO, NO2, and O3 could explain this discrepancy. Either explanation will have important implications for global tropospheric chemistry and for the interpretation of satellite observations of NO2.
For more: Silvern et al., 2018
Using satellite observations of tropospheric NO2 columns to infer long-term trends in US NOx emissions: the importance of accounting for the free tropospheric NO2 background
The US EPA reports a steady decrease in nitrogen oxide (NOx) emissions from fuel combustion over the 2005-2017 time period, while satellite observations show a leveling off after 2009 suggesting emission reductions and related air quality gains have halted. We show that the sustained decrease in NOx emissions is in fact consistent with observed trends in surface NO2 and ozone concentrations, and that the flattening of the satellite trend reflects a growing influence from the non-anthropogenic background.
For more: Silvern et al. (2019)