Estimation of Biogenic VOC Emissions in the Czech Republic

Characteristics of biogenic VOC as well as methodology of BVOC emission estimation are presented in this article. Biogenic emissions of VOC were estimated using semi-empirical model proposed by Guenther et al., 1995. Terms of formation, amount, spatial distribution of tropospheric ozone and the contribution of biogenic sources of VOC to ozone precursors were studied using numerical model for summer photochemical smog simulation (SMOG model, see Bednar et al., 2001). North-eastern part of the Czech Republic (Hruby Jesenik area) was selected as a model domain. Two representative points of the model grid were selected for comparison of two model runs with measured data. In the first run of the SMOG model only anthropogenic sources of VOC were taken into account, natural sources of VOC were added in the second run of the model. Introduction Tropospheric ozone O3 is a significant element of atmospheric pollution, especially in the summer period when photochemical reactions, which lead to ozone formation, are remarkably enhanced by intensive sunlight and high temperatures. Main ozone precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOC) are released to the atmosphere not only from anthropogenic sources, but they are emitted in considerable amounts from biogenic sources as well. Biogenic VOC (BVOC) are released from various sources such as marine and fresh water, soils and sediments, are produced during microbiological decomposition of organic material, but the main BVOC emitters are plant foliage and woody material (Guenther et al., 1995). Therefore majority of natural emissions in the Czech Republic are expected to originate from deciduous, coniferous and mixed forests. Laboratory and outdoor measurements have shown that plants emit wide spectrum of VOC, where isoprene (C5H8) and monoterpenes (C10H16) are considered to be the most prominent (Simpson et al., 1995). Purpose and processes of VOC production in plants are subjects of research and are not yet well understood, but recent studies have shown that VOC are released in case the plant is wounded or under unfavourable external conditions. Emissions are thought to act as a deterrent against parasites and herbivores and may be involved in plant protection against environmental stress such as foliar or root damage, polluted ambient air etc. (e.g. Kesselmeier et al., 1999). On the other hand VOC accumulated in flowers lure insect to pollinate plants. Since release of VOC has a significant dependence on temperature and solar radiation, due to control of plant stomata development, emissions of BVOC have diurnal and annual variation. Release of these gaseous compounds has a strong effect on chemical and physical properties of the atmosphere. VOC are crucial element in chemical reactions leading to ozone formation and accumulation in the troposphere. The main source of ozone in the lower atmosphere is photochemical decomposition of NO2 forming molecule of NO and single oxygen which is promptly combined with O2 molecule and produces ozone. At the same time ozone is being removed from atmosphere through oxidizing reaction of NO. In the system of these two source and sink reactions stable concentration of ozone would be established. Unfortunately this is not observed in the atmosphere. Real ozone concentrations are much higher than concentrations expected from pure NO2 and NO system (Fiala, Zavodsky, 2003) therefore there must be other element affecting this chemical cycle and causing storage of ozone in the atmosphere. Such elements are peroxyl radicals RO2 which are products of reaction between VOC and hydroxyl radical OH. Since radicals RO2 replace ozone in oxidizing reaction of nitrogen oxide NO, ozone is not removed from the atmosphere and may appear in high concentrations forming photochemical smog. Further consequence of interaction between VOC and WDS'07 Proceedings of Contributed Papers, Part III, 145–149, 2007. ISBN 978-80-7378-025-8 © MATFYZPRESS