| Carbonyl compounds and BTEX are import organic pollutants in the urban atmosphere. These compounds have been received attentions due to their potential adverse health effects on humans and their important role in atmospheric chemistry. In this study, indoor and outdoor concentration levels of twenty-one carbonyl compounds and five BTEX (benzene, toluene, ethylbenzene and xylenes) were measured in four hospitals of Guangzhou. The experiment method was based on US EPA. Also, the seasonal variation of carbonyl compounds in Guangzhou was studied.For hospital, its air quality is very important, especially for the patients. The study of carbonyl compounds and BTEX in hospitals are valuable. The results of our study were described as follows: For indoor compounds, acetone was the most abundant carbonyl compound, followed by acetaldehyde and formaldehyde, accounted for 26.5% ~ 38.5%, 11.2% ~ 22.3%, 5.3%~18.4% of the total carbonyl concentrations, respectively;Toluene was the most abundant of 5 BTEX, which accounted for 7.7% ~ 49.2% of the total BTEX concentrations. It was found that the I/O values of most carbonyls and BTEX were > 1, suggesting the indoor sources of the compounds. The lower correlations between carbonyls and BTEX concentrations showed the complex sources, such as the emission of vehicular exhaust, industrial, plants, building and decoration materials, medicines of hospital, etc. The C1/C2 ratios value in present study was 0.82 (lower than that of the previous studies). The relatively high level of acetaldehyde concentrations might result from the evaporation and oxidation of the widely used ethanol in hospital, which also reduced the concentration rate of C1/C2. The exposure risks of formaldehyde and acetaldehyde in hospitals, 1.1×10-4, 2.8×10-5, respectively, were lower comparing to other studies: The exposure risks in office and ballroom were3.4×10-4, 4.3×10-5and 4.4×10-4, 22.6×10-5, respectively (Baez et al., 2003;Feng et al., 2004). The highest benzene concentration in hospital was 23.3μg/m3, which was below the US limit (the 30min ambient air quality standard, 30μg/m3). It implied the air quality of hospitals was good according to carbonyl compounds and BTEX. To get further informationof the source of carbonyl and BTEX in hospital, another study was carried out, the result showed that the indoor concentrations of the compounds in medical rubbish room and some other places of hospital were much higher than those of outdoors, which might mean the sources of the carbonyl compounds and BTEX in the hospital. The concentration variation of indoor carbonyl compounds was related to the outdoor concentrations of carbonyl compounds. In China, few works on seasonal variation of ambient carbonyl compounds were performed, and for Guangzhou, these contents were not mentioned in the previous studies (Tang, 2002;Feng, 2005). In our study, two sites (Liwan and Wushan) were selected to study seasonal variation of ambient carbonyl compounds in Guangzhou. The results were as follows: Acetone (1.36-32.2 ug/m3) was the most abundant carbonyl compounds, followed by acetaldehyde (0.17-49.3ug/m3), formaldehyde (0.18-24.7ug/m3), butyraldehyde (0.16-26.3ug/m3) and 2-butanone (0.03-13.4|j,g/m3). Most carbonyl compound concentrations were higher in Liwan than those in Wushan, which might be resulted from the emission of plants and tobacco smoke in Liwan. Carbonyl compounds concentrations were higher in summer (July) than those in other seasons, which might be due to the stronger photochemical reaction in summer. There were no obvious regular variations of carbonyl compounds in daytime and nighttime in this study. During our study period, heavy haze appeared in the late November and early December in Guangzhou, the carbonyl compounds were measured to show the highest concentrations of most carbonyl compounds.
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