Abstract:
In recent years, the concentrations of multiple air pollutants in China have been reduced yet the reduction of surface ozone (O
3) concentration is not satisfactory compared to that of fine particulate matter (PM
2.5). The co-occurrence of PM
2.5 and O
3 pollution has occurred from time to time. To develop emission reduction strategy for PM
2.5 and O
3 on concurrent pollution days, the emission reduction effects of anthropogenic NO
x and volatile organic compounds (VOCs) in Shanghai were simulated using a three-dimensional meteorological-air quality model for the period of April 27—30, 2018, when PM
2.5 and O
3 both exceeded the national standard in Shanghai. Simulation results show that Shanghai was mostly under VOCs-controlled during the modeling period with a peak ratio (PR) of 0.6-1.1 in terms of the maximum daily eight-hour average (MDA8) O
3. A VOCs/NO
x reduction ratio (VNr) of at least 1.9:1 is needed to prevent ozone increase during emission reduction maintain the MDA8 O
3 concentration in Shanghai. For the reduction of PM
2.5 concentration, regional transport, SOA response to precursors and the diurnal variations in NO
3- production are important factors. Compared to the local emission reduction in Shanghai, both emission reduction advanced in time and jointly in region can further reduce the MDA8 O
3 concentration in Shanghai by 0.6%-3.0%. However, under the regional emission reduction scenario, PM
2.5 concentration in the downwind (i.e. southwestern Jiangsu) can be effectively reduced whereas PM
2.5 concentration slightly increased in Shanghai due to increases of the secondary inorganic components in PM
2.5. Advanced emission reduction (by three days ahead of pollution days) is more effective than regional reduction in terms of reducing PM
2.5 concentration in Shanghai. In order to effectively reduce both MDA8 O
3 and PM
2.5 concentrations, the emission reduction plan should be consider the local emissions of VOCs and NO
x in different regions as well as the meteorological conditions. To effectively achieve reductions inPM
2.5 concentration, attention also needs to be paid to the emission reduction of primary particulate matter and other gaseous precursors (e.g. SO
2, NH
3).