Characteristics of PM_2.5 and carbonaceous aerosols in Xi'an

Daily PM_2.5, organic carbon (OC), and elemental carbon (EC) were measured during 2012.3-2013.2 to study the temporal variations of PM_2.5 and carbonaceous aerosols. PM_2.5 showed a fluctuation from 26.9 to 505.1 μg/m³ during the sampling period. The annual average PM_2.5 mass concentration was 114.0±86.6 μg/m³, exceeding the Chinese air quality standard (GB 3095-2012) for PM_2.5 (35 μg/m³) by a factor of 3.3. The seasonal patterns ranked in descending order as follows, winter>autumn>spring>summer. The average concentrations for OC and EC were 21.44±15.76 and 6.16±3.38 μg/m³. OC/EC ratios ranged from 1.80 to 5.84, with the average being 3.37±0.95, suggesting the presence of secondary organic aerosols in atmosphere. Results of principal component analysis showed that major sources of carbonaceous aerosols include gasoline-and diesel-fueled vehicles, secondary aerosols and biomass burning.