Ambient BTX Observation nearby Main Roads In Hefei during Summer Time

ABSTRACT

In order to study the sources, chemical evolutions and impacts on air quality of BTX (benzene, toluene, xylene, etc.) in a typical unban area, a field campaign was conducted with our homemade differential optical absorption spectroscopy (DOAS) instrument in May 2014 at the North part of First Ring Road of Hefei. During the entire measurement, BTX showed high levels in the morning and at night except toluene and phenol. The observed average of benzene is 5.11 µg m^–3, toluene is 19.15 µg m^–3, m-xylene is 14.74 µg m–3, p-xylene is 1.47 µg m^–3, phenol is 0.67 µg m^–3, which are at a low pollution level compared with other cities. The ratios of toluene to benzene range from 1.6 to 8 and the correlation coefficient R of benzene and CO is about 0.88, suggesting the main source of local BTX is traffic emissions. Phenol shows negative correlation with benzene (R = 0.87) in the afternoon, which means that the oxidization of benzene by OH radicals is an important source of phenol. The relations with meteorological conditions were also disscussed, indicating the contribution of solvent evaporation from nearby point sources to toluene in the afternoon. Wind speed is another important factor to the concentration distribution of BTX. The correlation coefficient R of benzene and PM2.5 is 0.83, inferring the influence of street traffic emission on roadside pollution levels.