The relationship of meteorological and anthropogenic factors to time series measurements of CFC-11, CFC-12, and CH 3CCl 3 concentrations in the urban atmosphere
Continuous hourly measurements of the atmospheric concentrations of the halocarbons, CFC-12, CFC-11, CFC-113, CH 3CCl 3, and CCl 4, were conducted in the urban environment of Lukang, Changhua, in central Taiwan from January to November 2006. CFC-12, CFC-11 and CH3CCl 3 displayed significant concentration variability and were selected as target compounds (along with traffic released CO) for analysis of time series concentration variations of these species modulated by anthropogenic emissions and meteorology in this area. Among these compounds, distinct diurnal cycles of CO and CH3CCl 3 were observed throughout four seasons although a smaller concentration variability of these two species was found in summer. A similar diurnal cycle was found for CFC-11 except that the minimal concentration variability of CFC-11 was found in winter. In contrast to CH 3CCl 3 and CO, a pattern of diurnal and seasonal cycles was not found for CFC-12, of which the concentration variability was noticeably small in winter (from January to February) and not very different among other seasons. The concentration variability of CFC-11 and CFC-12 was driven by anthropogenic emissions and meteorology in fairly complicated ways. The concentration variability of CH 3CCl 3 and CO was likely modulated mainly by meteorology because anthropogenic emission rates of these two species were approximately constant. The small concentration variability of CFC-11 and CFC-12 in winter, especially the latter, was probably due to small emission of these two species from air conditioners in the cold season. The complicated seasonal and diurnal cycles of CFC-12 and CFC-11 induced by both anthropogenic emissions and meteorology were deconvoluted by using CFC-12/CH 3CCl 3 and CFC-11/CH 3CCl 3 ratios to eliminate the meteorological factor. Monthly trends of CFC-12/CH 3CCl 3 and CFC-11/CH 3CCl 3, representing anthropogenic emissions, were similar to that of ambient temperature.