Insights from ozone and particulate matter pollution control in New York City applied to Beijing

Strict emission control policies implemented in two megacities of New York City (NYC) and Beijing show impacts on the non-linear relationship of their ozone (O3) and fine particulate matter (PM2.5) during summertime. Here we show these non-linear O3-PM2.5 relationships including a positive linear part reflecting the O3/PM2.5 co-occurrence and a negative power function part reflecting the O3 formation suppression by PM2.5 based on the multiyear surface observations. The control policies targeting sulfur dioxide and PM2.5, then volatile organic compounds and nitrogen oxides, changed the PM2.5 chemical composition which resulted in an increased linear slope that indicates a weaker O3 control effect than occurred for PM2.5. These policies also enhanced the relative PM2.5 suppression effect as shown by an increase in the power function coefficient. Model simulations suggest that regional equal percentage emission reductions for Beijing and other Chinese megacities will be necessary to avoid further increase in the O3/PM2.5 linear slope and continuing occurrences of high levels of ozone.