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High concentrations (>15μm3 cm−3) of CaSO4, Ca(NO3)2 and (NH4)2SO4 were selected as surrogates of dry neutral, aqueous neutral and dry acidic inorganic seed aerosols, respectively, to study the effects of inorganic seeds on secondary organic aerosol (SOA) formation in irradiated m-xylene/NO x photooxidation systems. The results indicate that neither ozone formation nor SOA formation is significantly affected by the presence of neutral aerosols (both dry CaSO4 and aqueous Ca(NO3)2), even at elevated concentrations. The presence of high concentrations of (NH4)2SO4 aerosols (dry acidic) has no obvious effect on ozone formation, but it does enhance SOA generation and increase SOA yields. In addition, the effect of dry (NH4)2SO4 on SOA yield is found to be positively correlated with the (NH4)2SO4 surface concentration, and the effect is pronounced only when the surface concentration reaches a threshold value. Further, it is proposed that the SOA generation enhancement is achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of dry (NH4)2SO4 seed aerosols. [Copyright &y& Elsevier]

Abstract: We show that Aura Ozone Monitoring Instrument (OMI) nitrogen dioxide (NO2) tropospheric column data may be used to assess changes of the emissions of nitrogen oxides (NO x ) from power plants in the United States, though careful interpretation of the data is necessary. There is a clear response for OMI NO2 data to NO x emission reductions from power plants associated with the implementation of mandated emission control devices (ECDs) over the OMI record (2005–2011). This response is scalar for all intents and purposes, whether the reduction is rapid or incremental over several years. However, it is variable among the power plants, even for those with the greatest absolute decrease in emissions. We document the primary causes of this variability, presenting case examples for specific power plants. [ABSTRACT FROM AUTHOR]