China is facing dual pressures to reduce both PM 2.5 and O 3 pollution, the crucial precursors of which are NO x and VOCs. In our study, the role of NO x in both secondary organic aerosol (SOA, the important constituent of PM 2.5 ) and O 3 formation was examined in our 30 m 3 indoor smog chamber. As revealed in the present study, the NO x level can obviously affect the OH concentration and volatility distribution of gas-phase oxidation products and thus O 3 and SOA formation. Reducing the NO x concentration to the NO x -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 NO x at different VOC levels. The atmospheric implications of NO x in the coordinated control of PM 2.5 and O 3 are also discussed.
Nitrate photolysis is a vital process
in secondary NOx
release
into the atmosphere. The heterogeneous oxidation of SO2 due to nitrate photolysis has been widely reported, while the influence
of SO2 on nitrate photolysis has rarely been investigated.
In this study, the photolysis of nitrate on different substrates was
investigated in the absence and presence of SO2. In the
photolysis of NH4NO3 on the membrane without
mineral oxides, NO, NO2, HONO, and NH3 decreased
by 17.1, 6.0, 12.6, and 57.1% due to the presence of SO2, respectively. In the photolysis of NH4NO3 on the surface of mineral oxides, SO2 also exhibited
an inhibitory effect on the production of NOx, HONO, and NH3 due to its reducibility and acidic products, while the increase
in surface acidity due to the accumulation of abundant sulfate on
TiO2 and MgO promoted the release of HONO. On the photoactive
oxide TiO2, HSO3
–, generated
by the uptake of SO2, could compete for holes with nitrate
to block nitrate photolysis. This study highlights the interaction
between the heterogeneous oxidation of SO2 and nitrate
photolysis and provides a new perspective on how SO2 affects
the photolysis of nitrate absorbed on the photoactive oxides.
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