Smog Chamber Study on the Role of NOx in SOA and O3 Formation from Aromatic Hydrocarbons

China is facing dual pressures to reduce both PM(2.5 )and O(3 )pollution, the crucial precursors of which are NOx and VOCs. In our study, the role of NOx in both secondary organic aerosol (SOA, the important constituent of PM2.5) and O(3 )formation was examined in our 30 m(3 )indoor smog chamber. As revealed in the present study, the NOx level can obviously affect the OH concentration and volatility distribution of gas-phase oxidation products and thus O(3 )and SOA formation. Reducing the NOx concentration to the NOx-sensitive regime can inhibit O(3 )formation (by 42%), resulting in the reduction of oxidation capacity, which suppresses the SOA formation (by 45%) by inhibiting the formation of O-and N-containing gas-phase oxidation products with low volatility. The contribution of these oxidation products to the formation of SOA was also estimated, and the results could substantially support the trend of SOA yield with NOx at different VOC levels. The atmospheric implications of NOx in the coordinated control of PM2.5 and O(3 )are also discussed.