Abstract
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 a 20% increase in North American (NA) isoprene and a 20% decrease in NA anthropogenic emissions (nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC) and NOx + NMVOC + carbon monoxide + aerosols). The surface O3 response to NA isoprene emissions (ΔO3_ISOP) in surface air over NA is about one third of the response to all NA anthropogenic emissions (ΔO3_ANTH; although with different signs). Over intercontinental distances, ΔO3_ISOP is relatively larger; in summer and fall, ΔO3_ISOP in surface air over Europe and North Africa (EU region) is more than half of ΔO3_ANTH. Future increases in NA isoprene emissions could thus offset decreases in EU surface O3 resulting from controls on NA anthropogenic emissions. Over the EU region, ΔPAN_ISOP at 700 hPa is roughly the same magnitude as ΔPAN_ANTH (oppositely signed). Outside of the continental source region, the percentage changes in PAN are at least twice as large as for 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).
Highlights
A recent internationally coordinated effort has estimated hemispheric pollutant transport at northern mid-latitudes and assessed uncertainties in these estimates (TFHTAP, 2007)
The slightly larger peroxy acetyl nitrate (PAN) ISOP at 700 hPa over the Europe and North Africa (EU) region may partially reflect the transport of hydroxyacetone, an intermediate isoprene oxidation product with a lifetime of days, which further reacts to produce methyl glyoxal and the peroxy acetyl radical, which may lead to additional PAN formation in the presence of nitrogen oxides (NOx)
With the MOZART-2 global chemical transport model, we examined the influence of isoprene versus anthropogenic emissions from North America (NA) on intercontinental O3 www.atmos-chem-phys.net/11/1697/2011/
Summary
A recent internationally coordinated effort has estimated hemispheric pollutant transport at northern mid-latitudes and assessed uncertainties in these estimates (TFHTAP, 2007). Of particular relevance for O3 produced in the source regions is the uncertain interaction of isoprene with the NOx budget via isoprene nitrate formation; the ultimate influence of isoprene on O3 may hinge on the poorly understood fate of isoprene nitrates (e.g., von Kuhlmann et al, 2004; Ito et al, 2009; Perring et al, 2009; Paulot et al, 2009; Weaver et al, 2009) While we expect these uncertainties to contribute to model diversity in “baseline” simulations for the present atmosphere, it is unclear whether they are contributing to the range in model estimates of the responses of surface O3 and NOy deposition to anthropogenic emission perturbations, as reported in prior TF HTAP publications (Sanderson et al, 2008; Fiore et al, 2009; Reidmiller et al, 2009). We evaluate the impact of uncertainties in isoprene emissions and chemistry on estimates of hemispheric responses to NA anthropogenic emission controls (Sect. 6) and discuss the implications of our findings (Sect. 7)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
