Organic Carbon and Elemental Carbon in Two Dust Plumes at a Coastal City in North China

Abstract

In the spring of 2023, two severe dust events occurred in the coastal city of Qinhuangdao, North China. We investigated organic carbon (OC) and elemental carbon (EC) in PM10 using an OC/EC analyzer and identified the morphology and elemental composition of individual dust particles using a scanning electron microscope coupled with energy-dispersive X-ray (SEM-EDX). Results showed that OC mass concentrations varied significantly from 12.6 µg m -3 to 74.6 µg m -3 and showed a significant positive correlation with the PM10 mass concentration. On average, OC made up 4.6% ± 1.1% and 4.3% ± 0.6% of the total PM10 mass in two dust periods. Particularly, the weight ratio of OC-to-coarse particles (PM2.5-10) was stable at approximately 2.8% ± 0.2%. In contrast, EC was less than 1.0% of the total PM10 mass, with an average value of 0.13% ± 0.26% and 0.28% ± 0.15% in two dust periods. According to SEM-EDX results, the average weight ratios of sulfur on detected individual dust particles were 0.48% and 1.88% in two dust periods, which were less than the previously reported value in non-dust days, indicating inefficient formation of secondary species on the dust particles. SEM-EDX analysis further revealed that approximately 5.2% of the particles (in number) were irregularly shaped C-dominated particles, which might be carbonaceous species-containing particles. These results highlighted that the dust plumes brought a certain amount of OC but limited EC from dust sources.