February 2nd, 2011
Changing land-use and climate may increase biogenic isoprene emissions, which could offset the benefits from North American air pollution controls for both domestic and European air quality (surface ozone). Both anthropogenic and biogenic emission changes are reflected in peroxy acetyl nitrate (PAN), which may serve as a more effective indicator of intercontinental emission changes than ozone itself.
We also examine changes in PAN at 700 hPa for two reasons: (1) this level should reside in the lower free troposphere and thus reflect the composition of air masses that are available to subside and mix into the continental boundary layer, and (2) this altitude is a region of the atmosphere that can be sampled with ground-based instruments in mountainous regions. Both NA anthropogenic and isoprene emission changes exert a larger relative influence on PAN at 700 hPa, as compared to surface O3 (compare top and bottom). This result implies that long-term PAN measurements at high altitude sites may help to detect O3 precursor emission changes.
For more information please see Fiore, Arlene M., Hiram Levy II, and D A Jaffe (2011): North American isoprene influence on intercontinental ozone pollution. Atmospheric Chemistry and Physics, 11(4), doi: 10.5194/acp-11-1697-2011.