Variation Characteristics of Ambient NMHCs at Shangdianzi and Lin'an Regional GAW Sites

In order to study the variation characteristics of concentration of the atmospheric non-methane hydrocarbons (NMHCs) in background area of China, the atmospheric concentrations of NMHCs were measured at Lin'an (LA) regional GAW (Global Atmosphere Watch) Station (30°250'N , 119° 440'E; 132.0 m ASL)and Shangdianzi (SDZ) regional GAW Station (40°190'N , 117°07'E; 286.5 m ASL) with the sorbent sorption/thermal desorption/gas chromatographic method. Totally 145 samples were collected during the period of October 2003 and July 2004. Among the 52 NMHC species of C2-C10 detected there were 26 alkanes,17 alkenes, and 9 aromatics. The average concentrations of total NMHCs (TNMHCs) at LA and SDZ were(238.5±126.0) 10-9C and (278.7±185.5) 10-9C, respectively. The results showed the ambient concentrations of TNMHCs at LA regional GAW Station increased notably over the last decade. The compositions of NMHCs at SDZ and LA were relatively similar. The proportions of alkanes, alkenes, and aromatics for SDZ and LA were in ranges of (27.3±4.0)%, (10.3±3.5)%, and (62.5±4.8)%,respectively, with features of vehicle exhaust emissions. The concentrations of NMHCs at the two sites showed obvious diurnal and seasonal variations. The TNMHC concentrations in October-November were high at the two sites, and relatively low in April and July. The diurnal variation patterns at the sites were different. The high TNMHC concentrations at SDZ normally appeared in evening and night, but appeared in morning at LA. The TNMHCs concentrations at the two sites were significantly influenced by the meteorological condition. The high TNMHC concentration associated with the local wind from the urban areas or trafic in upper reaches.