Effect of isoprene emissions from major forests on ozone formation in the city of Shanghai, China

The assessment of the impact of isoprene on ozone formation suggests that the concentrations of peroxy radicals (RO(2)) are significantly enhanced due to the oxidation of isoprene, with a maximum of 30 ppt. However, the enhancement of RO(2) is confined to the forested regions. Because the concentrations of NO(x) were low in the forest regions, the ozone production due to the oxidation of isoprene (C(5)H(8) + OH ->-> RO(2) + NO ->-> O(3)) is low (less than 2-3 ppb h(-1)).

The calculation further suggests that the oxidation of isoprene leads to the enhancement of carbonyls (such as formaldehyde and acetaldehyde) in the regions downwind of the forests, due to continuous oxidation of isoprene in the forest air. As a result, the concentrations of HO(2) radical are enhanced, resulting from the photo-disassociation of formaldehyde and acetaldehyde. Because the enhancement of HO(2) radical occurs in regions downwind of the forests, the enhancement of ozone production (6-8 ppb h(-1)) is higher than in the forest region, causing by higher anthropogenic emissions of NO(x).

This study suggests that the biogenic emissions in the major forests to the south of Shanghai have important impacts on the levels of ozone in the city, mainly due to the carbonyls produced by the continuous oxidation of isoprene in the forest air.