PM2.5 Suppression of Ozone Formation at High Mass Loading
JAMES SCHWAB, Jie Zhang, Alexandra Catena, Janie Schwab, Matthew Ninneman, Junfeng Wang, Amanda Teora,
Atmospheric Sciences Research Center, University at Albany Abstract Number: 212
Working Group: Urban Aerosols
AbstractRecent work has highlighted the relationship between PM
2.5 and O
3 and the interplay of these two important pollutants in areas that suffer high pollution loading. Following the US National Ambient Air Quality Standards (NAAQS), we have analyzed summertime maximum daily 8-h average ozone (MDA8 O
3) in relation to the daily average PM
2.5 (DA24 PM
2.5). At low PM concentrations (below 20 or 25 µg/m
3), the two pollutants show a direct linear relationship. At higher PM concentrations the relationship curves and levels off - or even decreases. The flat or declining relationship has been partly attributed to the scavenging of HO
2 or NO
3 radicals, or to reduced photolysis rates due to the higher PM loading. We have fit a non-linear polynomial function to this full relationship and obtained a three term solution, with a linear term describing the O
3/PM
2.5 co-occurrence, a negative power function term reflecting the PM suppression of O
3 formation, and a constant term. We evaluate the PM suppression factor (the coefficient of the power function term) for a number of different locations in the Eastern US over the past 20 years. Detailed PM chemical composition measurements at NYC from four measurement periods over the study period allow us to interpret the reason for changes in the PM suppression factor. Inclusion of an additional eleven city sites in the Eastern US allows a more complete picture of the spatial and temporal variations and trends of the suppression factor. Finally, we examine the relationship between the PM suppression factor and the satellite measurements of the HCHO/NO
2 ratio (a frequently used indicator of the ozone production regime). The strong association between these two quantities leads us to conclude that the PM suppression factor can also be a useful measure of the ozone production regime.
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