Abstract
Abstract. Hourly measurements of 13 volatile hydrocarbons (C2–C7) were performed at an urban background site in Zurich (Switzerland) in the years 1993–1994 and again in 2005–2006. For the separation of the volatile organic compounds by gas-chromatography (GC), an identical chromatographic column was used in both campaigns. Changes in hydrocarbon profiles and source strengths were recovered by positive matrix factorization (PMF). Eight and six factors could be related to hydrocarbon sources in 1993–1994 and in 2005–2006, respectively. The modeled source profiles were verified by hydrocarbon profiles reported in the literature. The source strengths were validated by independent measurements, such as inorganic trace gases (NOx, CO, SO2), methane (CH4), oxidized hydrocarbons (OVOCs) and meteorological data (temperature, wind speed etc.). Our analysis suggests that the contribution of most hydrocarbon sources (i.e. road traffic, solvents use and wood burning) decreased by a factor of about two to three between the early 1990s and 2005–2006. On the other hand, hydrocarbon losses from natural gas leakage remained at relatively constant levels (−20%). The estimated emission trends are in line with the results from different receptor-based approaches reported for other European cities. Their differences to national emission inventories are discussed.
Highlights
Air pollutants can have adverse impacts on human health, most notably on the respiratory system and circulation (Nel, 2005), acidify and eutrophicate ecosystems (Matson et al, 2002), diminish agricultural yields, corrode materials and buildings (Primerano et al, 2000), and decrease atmospheric visibility (Watson, 2002)
Volatile organic compounds (VOCs) have several important impacts: while only some of them are toxic to humans, e.g. benzene (WHO, 1993), or relevant greenhouse gases, e.g. methane (Forster et al, 2007), all VOCs are oxidized in the atmosphere and most are thereby involved in the formation of secondary pollutants, such as ozone (O3), and secondary organic aerosol (SOA)
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Summary
Air pollutants can have adverse impacts on human health, most notably on the respiratory system and circulation (Nel, 2005), acidify and eutrophicate ecosystems (Matson et al, 2002), diminish agricultural yields, corrode materials and buildings (Primerano et al, 2000), and decrease atmospheric visibility (Watson, 2002). Volatile organic compounds (VOCs) have several important impacts: while only some of them are toxic to humans, e.g. benzene (WHO, 1993), or relevant greenhouse gases, e.g. methane (Forster et al, 2007), all VOCs are oxidized in the atmosphere and most are thereby involved in the formation of secondary pollutants, such as ozone (O3), and secondary organic aerosol (SOA). Ambient VOC measurements became important since the 1950s (Eggertsen and Nelsen, 1958) due to summer smog phenomena, first and foremost due to high O3 levels in the Los Angeles basin. The identification and quantification of VOC sources is a necessary step to mitigate air pollution. Receptor models were developed to attribute measured ambient air pollutants to their emission sources. Depending on the degree of prior knowledge of the sources, a chemical mass balance (CMB; composition of the emission sources is known), a multivariate receptor model (no a priori knowledge) or a hybrid model in between these extreme cases is most appropriate
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