Enhanced summertime PM_2.5-suppression of O₃ formation over the Eastern US following the O₃-sensitivity variations

The suppression of ozone (O-3) formation due to the presence of fine particulate matter (PM2.5) has recently been highlighted for further O-3 pollution controls in regions that suffer high ozone concentrations. Here we derive multiple PM2.5-suppression factors for the Eastern United States (U.S.) major cities based on a non-linear fitting of the PM2.5 and O-3 relationship from the multiyear surface observations. Our results show that these PM2.5-suppression factors are increasing with time and generally follow the transition of the O-3-sensitive regime towards NOx-limited chemistry. A spatial discrepancy of this suppression factor is seen currently with a higher value in the Southeastern U.S. than in the Northeastern U.S. A spatial similarity between urban regions and their downwind locations was observed for the New York City metro area. This more extensive formulation of the PM2.5-suppression factor will further improve the ability of models to help guide O-3 and PM2.5 concentration pollution controls.