Diagnosing the Sensitivity of Particulate Nitrate to Precursor Emissions Using Satellite Observations of Ammonia and Nitrogen Dioxide

Abstract

Particulate nitrate is a major component of fine particulate matter (PM2.5). Its formation may be varyingly sensitive to emissions of ammonia (NH3), nitrogen oxides (NOx ≡ NO + NO2), and volatile organic compounds (VOCs), depending on local conditions. Diagnosing these sensitivities is critical for successful air quality management. Here, we show that satellite measurements of tropospheric NH3 and NO2 columns can be used as a quick indicator of the dominant sensitivity regime through the NH3/NO2 column ratio together with the NO2 column. We demonstrate the effectiveness of this indicator with the GEOS-Chem chemical transport model and define thresholds to separate the different sensitivity regimes. Applying the method to wintertime IASI and OMI observations in East Asia reveals that surface nitrate is dominantly VOC-sensitive in the southern North China Plain (NCP), NOx-sensitive in most of the East China Plain, and NH3-sensitive in the northern NCP, southern China, and Korea.