Aromatic Hydrocarbons and Halocarbons at a Mountaintop in Southern China

ABSTRACT

In this study, 45 ambient samples were collected in the summer of 2011 and spring of 2012 on Mount Lushan. The concentrations and seasonal distributions of aromatic hydrocarbons and halocarbons were measured and discussed. Moderate concentrations of individual species were found compared with other mountain sites; however, the measured concentrations were much lower than the values reported in cities. For aromatic hydrocarbons, benzene and m/p-xylene were the most abundant species in the spring, while benzene and toluene exhibited the largest contributions in the summer. For halocarbons, the concentrations of 1,2,4-trichlorobenzene, dichlorodifluoromethane and chloromethane were higher than other gases measured in the spring; and dichlorodifluoromethane and chloromethane contributed largest in the summer. The OH loss rates demonstrated that 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene were the dominant aromatic hydrocarbons for OH loss rates in the spring, while styrene and toluene contributed the largest to reactivity in the summer. For the ozone formation potential (OFP), 1,2,4-trimethylbenzene and m/p-xylene accounted for the largest fraction of the OFPs in the spring (24.3% and 23.7%), while toluene was the most abundant source of OFP (i.e., 43.7%) in the summer. M/p-xylene exhibited large contributions to OFP in both spring and summer (23.7% and 19.2%) of the OFPs. The T/B (0.80 and 0.73 in spring and summer respectively) ratios indicated that the sampled air masses were primarily influenced by automotive emissions. The 36-h backward trajectories of the sampled air masses and the corresponding daily concentrations of individual species suggested that long-range transport had a large effect on the atmosphere at the sampling site.