Models and observations of the impact of natural hydrocarbons on rural ozone

Abstract

Large quantities of non-methane hydrocarbons (NMHCs) are emitted into the atmosphere from vegetation1,2. A recent inventory by Lamb et al.2 indicates that the emission of natural hydrocarbons is significant compared to that of anthropogenic NMHCs in most regions of the United States. Because of their chemical activity, the natural NMHCs can play important parts in the formation of trace gases, such as ozone (O3), peroxyacetyl nitrate (PAN) and oxygenated secondary hydrocarbons3–5, which contribute to regional-scale air pollution6 and may be harmful to crops and forest7–9. The impact of natural hydrocarbons on the formation of O3 in the atmosphere has been discussed previously4–13. In general, it has been concluded that their impact is small14–16. But lack of data on the ambient concentrations of key photochemical species and an incomplete analysis of the photochemistry has prevented a definitive evaluation of the impact of natural NMHCs on rural O3. Here we report on concentrations of key trace gases measured concurrently at a rural site in the eastern USA during the summer of 1986 and a modelling study conducted to analyse these measurements. This study demonstrates that natural NMHCs can have a significant impact on ozone formation in rural air.