Isoprene and monoterpenes over Russia and their impacts in tropospheric ozone formation

Abstract

Ground-based levels of important biogenic volatile organic compounds (BVOCs), isoprene and monoterpenes, as well as NOx and O3 measured simultaneously along the Trans-Siberian railway on a mobile railway laboratory in TROICA-12 campaign in summer 2008 are analyzed. It was shown that the highest isoprene (≥ 2.5 ppb) concentration was observed in the daytime in the Far East region where several favorable factors for its emissions occurred: a large amount of deciduous forests, high temperatures (>28°C) and light conditions. Maximum levels of monoterpenes (up to 3-9 ppb) along the Trans-Siberian railway were observed during the nighttime in the Ural region and in Central Siberia where coniferous vegetation is located. To evaluate the relative importance of isoprene and monoterpenes in ground-level ozone formation in Russian cities along the Trans-Siberian railway, where high NOx concentration leads to tropospheric ozone generation, daytime ozone-forming potential (OFP) was calculated. The chemical losses of the studied BVOCs during their transport from sources to the measurement point were taken into account. Calculated OFPs due to isoprene (OFPiso) and monoterpenes (OFPmono) along the Trans-Siberian railway are in average 15±13 and 18±25 ppbv of ozone, respectively. The highest OFPiso (up to 40 ppbv) were estimated in Central Siberia and in the Far East. OFPmono was the highest in the regions of coniferous vegetation, Ural and Central Siberia, and reached 80 ppbv. In the most cities along the Trans-Siberian railway, where high NOx concentration (10-20 ppbv) along with high daytime temperatures (>25°C) were observed, monoterpenes made a main contribution to tropospheric ozone formation. Only in the Far East cities, where the largest deciduous vegetation area of the Trans-Siberian railway is located, isoprene played the main role in tropospheric ozone generation. It was also noted that OFPiso increases with the population-size of the cities. It can be either due to the greater proportion of deciduous vegetation in the large cities along the Trans-Siberian railway or due to the impact of anthropogenic isoprene source. OFPmono the lowest in the medium cities and the highest in the small ones.

Keywords

• isoprene, monoterpenes, tropospheric ozone, biogenic volatile organic, ozoneforming potential, trans-siberian railway
• mobile laboratory
• troica