PM1 carbonaceous aerosols during winter in a typical valley city of western China: Vertical profiles and the key influencing factors

Abstract To fill the blank on vertical profiles of carbonaceous aerosols during winter, the first in situ vertical measurements of organic and elemental carbon (OC, EC) from ground level to 620 m were conducted by means of high topographic relief in a typical valley city of Lanzhou, northwest China. The key factors (meteorology and sources) affecting the vertical distributions also were revealed by clustering technique and principal component analysis. Mean OC and EC concentrations were (16.2 ± 8.9) μg m −3 and (5.1 ± 2.1) μg m −3 during the study periods near the ground. More uniformly vertical distributions of carbonaceous aerosols during daytime than those during nighttime with OC (EC) decreasing rates of ∼1.45 (∼0.32) μg m −3 100 m −1 during nighttime and ∼0.84 (∼0.09) μg m −3 100 m −1 during daytime. Three distinct types of OC (EC) vertical profiles were determined by clustering technique. The cluster with high concentrations of OC (33.7 ± 5.7 μg m −3 ) and EC (10.5 ± 7.7 μg m −3 ) near the ground surface was induced largely by temperature inversion around the ground. The OC (EC) differences between the surface and the hilltop increased by 14.21 (2.45) μg m −3 when inversion layer depth increased by 100 m. Winter carbonaceous aerosols were more significantly affected by atmospheric stratification near the ground, while those were impacted together by vertical and horizontal dispersions at the hilltop. The primary emissions from coal combustion or biomass burning for heating at the hilltop and motor vehicles near the ground also had an important effect on OC (EC) vertical profiles. The emissions from coal burning and gasoline vehicles accounted for 60%–70% of carbonaceous aerosols in urban areas of Lanzhou. Furthermore, the contributions of gasoline vehicles during daytime near the surface (∼20%) and biomass burning at the hilltop (∼15%) were larger due to the impact of human activities.