Atmos. Chem. Phys. Discuss., 10, 24821-24851, 2010
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
North American isoprene influence on intercontinental ozone pollution
A. M. Fiore1, H. Levy II1, and D. A. Jaffe2
1NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
2Department of Science and Technology, University of Washington-Bothell, Washington, USA

Abstract. Changing land-use and climate may alter emissions of biogenic isoprene, a key ozone (O3) precursor. Isoprene is also a precursor to peroxy acetyl nitrate (PAN) and thus affects partitioning among oxidized nitrogen (NOy) species, shifting the balance towards PAN which more efficiently contributes to long-range transport relative to nitric acid (HNO3) which rapidly deposits. With a suite of sensitivity simulations in the MOZART-2 global tropospheric chemistry model, we gauge the relative importance of the intercontinental influence of 20% changes in North American (NA) isoprene versus 20% changes in NA anthropogenic emissions (nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC) and NOx + NMVOC + carbon monoxide + aerosols). The regional NA surface O3 response to a 20% increase in NA isoprene is approximately one third of the response (oppositely signed) to a 20% decrease in all NA anthropogenic emissions in summer. The intercontinental surface O3 response over Europe and North Africa (EU region) to NA isoprene is more than half of the response to all NA anthropogenic emissions combined in summer and fall. During these seasons, natural inter-annual variations in NA isoprene emissions (estimated at ±10%) may modulate the responses of EU surface O3, lower tropospheric PAN, and total NOy deposition to a 20% decrease in NA anthropogenic emissions by ±25%, ±50%, and ±20%, respectively. Lower tropospheric PAN responds similarly for 20% perturbations to either NA isoprene or NA anthropogenic O3 precursor emissions. This PAN response is at least twice as large as the relative changes in surface O3, implying that long-term PAN measurements at high altitude sites may help to detect O3 precursor emission changes. We find that neither the baseline level of isoprene emissions nor the fate of isoprene nitrates contributes to the large diversity in model estimates of the anthropogenic emission influence on intercontinental surface O3 or oxidized nitrogen deposition, reported in the recent TF HTAP multi-model studies (TFHTAP, 2007).

Citation: Fiore, A. M., Levy II, H., and Jaffe, D. A.: North American isoprene influence on intercontinental ozone pollution, Atmos. Chem. Phys. Discuss., 10, 24821-24851, doi:10.5194/acpd-10-24821-2010, 2010.
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