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To advance our understanding on the factors that affect photochemical pollution at different elevations in mountainous areas, concurrent systematic field measurements (September to November 2010) were conducted at a mountain site and at an urban site at the foot of the mountain in Hong Kong. The mixing ratios of air pollutants were greater at the foot of the mountain (i.e., Tsuen Wan urban site, TW) than near the summit (i.e., Tai Mao Shan mountain site, TMS), expect for ozone. In total, only one O3 episode day was observed at TW, whereas twenty-one (21) O3 episode days were observed at TMS. The discrepancy of O3 at the two sites was attributed to the mixed effects of NO titration, vertical meteorological conditions, regional transport and mesoscale circulations. The lower NO levels at TMS and the smaller differences of "Oxidant" Ox (O3 + NO2) between the two sites suggested that variations of O3 at the two sites were partly attributed to different degree of NO titration. In addition, analysis of vertical structure of meteorological variables revealed that the inversion layer at the range of altitudes of 500-1000m might be another factor that caused the high O3 levels at TMS. Furthermore, analyses of the wind fields, the levels of air pollutants in different air flows, ratios of different trace gases and the correlation between variability and the lifetime of VOCs (volatile organic compounds) indicated that high O3 concentrations at TMS were somewhat influenced by regional air masses from the highly polluted Pearl River delta (PRD) region. In particular, the diurnal profiles and correlations of gaseous pollutants suggested influence of mesoscale circulations, which is confirmed using the Master Chemical Mechanism moving box model (Mbox) and the Weather Research and Forecasting (WRF) model. By investigating the correlations of observed O3 and NOx* and the relationships of O3 and its precursors by an observation-based model (OBM), as well as the ratios of VOC/NOx, it was concluded that photochemical O3 formation at TMS was mostly influenced by VOCs, with measurable impact of NOx, while O3 production at TW was generally limited by the concentrations of VOCs. This is the first report of the comprehensive analysis on the data of photochemical pollution obtained from concurrent measurements in mountainous areas in the PRD region. [ABSTRACT FROM AUTHOR]

Methacrolein (MACR) and methyl vinyl ketone (MVK) are major oxidation products of isoprene, but they also have primary emissions in urban environments, for example from fuel use. To examine whether MACR and MVK could be used as a direct measurement of the oxidation rate of isoprene in an urban setting, the diurnal variations of isoprene, MACR and MVK were characterized at an urban site in Hong Kong from September to November, 2010. Ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxides (NO x ) were simultaneously monitored. The average isoprene mixing ratio was 252 ± 204 pptv, with a bell-shaped distribution observed on most sampling days. Higher levels of isoprene were recorded in the beginning of the sampling period, when the temperature was higher. The average mixing ratios of MACR and MVK were 101 ± 85 pptv and 175 ± 131 pptv, respectively. While isoprene, MACR and MVK experienced peak concentrations from 11 a.m. to 3 p.m., increased levels of MACR and MVK during the morning rush hour did not coincide with isoprene. The low associations between isoprene and MACR/MVK suggest that either MACR/MVK were not formed from local isoprene oxidation and/or they could partly originate from primary emissions such as fuel evaporation or combustion. Statistical analyses of linear regression and positive matrix factorization revealed that approximately 20–29% of the measured MACR and MVK was associated with biogenic emissions, and 55–71% was impacted by vehicular emissions, particularly during morning rush hours. Since MACR and MVK originated from both primary emissions and biogenic emissions at this urban site, they can therefore overestimate the actual rate of isoprene oxidation and its contribution to O3 production in urban areas with strong primary emissions. [ABSTRACT FROM AUTHOR]

Abstract: Reduced sulfur compounds (RSCs) such as carbonyl sulfide (OCS), dimethyl sulfide (DMS) and carbon disulfide (CS2) impact radiative forcing, ozone depletion, and acid rain. Although Asia is a large source of these compounds, until now a long-term study of their emission patterns has not been carried out. Here we analyze 16 months of RSC data measured at a polluted rural/coastal site in the greater Pearl River Delta (PRD) of southern China. A total of 188 canister air samples were collected from August 2001 to December 2002. The OCS and CS2 mixing ratios within these samples were higher in autumn/winter and lower in summer due to the influence of Asian monsoon circulations. Comparatively low DMS values observed in this coastal region suggest a relatively low biological productivity during summer months. The springtime OCS levels in the study region (574 ± 40 pptv) were 25% higher than those on other East Asia coasts such Japan, whereas the springtime CS2 and DMS mixing ratios in the PRD (47 ± 38 pptv and 22 ± 5 pptv, respectively) were 3–30 times lower than elevated values that have been measured elsewhere in East Asia (Japan and Korea) at this time of year. Poor correlations were found among the three RSCs in the whole group of 188 samples, suggesting their complex and variable sources in the region. By means of backward Lagrangian particle release simulations, air samples originating from the inner PRD, urban Hong Kong and South China Sea were identified. The mean mixing ratio of OCS in the inner PRD was significantly higher than that in Hong Kong urban air and South China Sea marine air (p < 0.001), whereas no statistical differences were found for DMS and CS2 among the three regions (p > 0.05). Using a linear regression method based on correlations with the urban tracer CO, the estimated OCS emission in inner PRD (49.6 ± 4.7 Gg yr−1) was much higher than that in Hong Kong (0.32 ± 0.05 Gg yr−1), whereas the estimated CS2 and DMS emissions in the study region accounted for a very few percentage of the total CS2 and DMS emission in China. These findings lay the foundation for better understanding sulfur chemistry in the greater PRD region of southern China. [Copyright &y& Elsevier]

We present measurements of C1–C8 volatile organic compounds (VOCs) at four sites ranging from urban to rural areas in Hong Kong from September 2002 to August 2003. A total of 248 ambient VOC samples were collected. As expected, the urban and sub-urban sites generally gave relatively high VOC levels. In contrast, the average VOC levels were the lowest in the rural area. In general, higher mixing ratios were observed during winter/spring and lower levels during summer/fall because of seasonal variations of meteorological conditions. A variation of the air mass composition from urban to rural sites was observed. High ratios of ethyne/CO (5. 6pptv/ppbv) and propane/ethane (0. 50pptv/pptv) at the rural site suggested that the air masses over the territory were relatively fresh as compared to other remote regions. The principal component analysis (PCA) with absolute principal component scores (APCS) technique was applied to the VOC data in order to identify and quantify pollution sources at different sites. These results indicated that vehicular emissions made a significant contribution to ambient non-methane VOCs (NMVOCs) levels in urban areas (65±36%) and in sub-urban areas (50±28% and 53±41%). Other sources such as petrol evaporation, industrial emissions and solvent usage also played important roles in the VOC emissions. At the rural site, almost half of the measured total NMVOCs were due to combustion sources (vehicular and/or biomass/biofuel burning). Petrol evaporation, solvent usage, industrial and biogenic emissions also contributed to the atmospheric NMVOCs. The source apportionment results revealed a strong impact of anthropogenic VOCs to the atmosphere of Hong Kong in both urban/sub-urban and rural areas. [Copyright &y& Elsevier]