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Abstract
Ground-based levels of important biogenic volatile organic compounds (BVOCs), isoprene and monoterpenes, as well as NO x and O 3 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 NO x 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 (OFP iso ) and monoterpenes (OFP mono ) along the Trans-Siberian railway are in average 15±13 and 18±25 ppbv of ozone, respectively. The highest OFP iso (up to 40 ppbv) were estimated in Central Siberia and in the Far East. OFP mono 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 NO x 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 OFP iso 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. OFP mono the lowest in the medium cities and the highest in the small ones.
Highlights
One of the important consequences of human activity on the atmosphere is an increase in tropospheric ozone level
The highest ozone levels are often observed in urban environment, which is characterised by higher temperatures, and by higher levels of ozone precursors, nitrogen oxides (NOx), carbon monoxide (CO), methane (CH4) and volatile organic compounds (VOCs)
CO, CH4 and VOCs are mainly oxidized in the troposphere by OH radicals, and at high air temperature and solar radiation in NOx-polluted conditions can cause the formation of high ozone levels which pose a threat to human health (Sillman 1999)
Summary
One of the important consequences of human activity on the atmosphere is an increase in tropospheric ozone level. The atmospheric composition measurements over Russia along the Trans-Siberian railway in the unique TROICA (TRanscontinental Observations Into the Chemistry of the Atmosphere) experiments on a mobile laboratory in summer 2008 allowed the detailed analysis of the main BVOCs levels, isoprene and monoterpenes, over Russia and the estimation of their impact in tropospheric ozone formation.
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