Biomass burning contribution to regional PM<sub>2.5</sub> during winter in the North China

Abstract. Source apportionment of fine particles (PM2.5) at a background site in the North China in winter, 2014 was assessed by statistical analysis on the chemical species grouped by the trajectory clusters, radiocarbon (14C) measurement and the Positive Matrix Factorization (PMF) modeling linked with the 14C measurement. During the sampling period, the concentration of PM2.5 was 77.6 ± 59.3 μg m−3, and the sulfate concentration was the highest, followed by nitrate, organic carbon (OC), elemental carbon (EC) and ammonium, respectively. Demonstrated by the backward trajectory, more than half of PM2.5 was found from the Beijing-Tianjin-Hebei (BTH) region, followed by the Mongolia and the Shandong Peninsula. The cluster analysis showed that PM2.5 from the Shandong Peninsula had an obvious signal of biomass burning emission, while that from the BTH region showed vehicle emission pattern. The finding was further confirmed by the radiocarbon measurement of OC and EC in two merged samples selected from a successive synoptic process. The 14C measurement indicated that biogenic and biomass burning emission contributed 59 % and 52 % to OC and EC concentrations when air masses originated from the Shandong Peninsula, and the contributions fell to 46 % and 38 %, respectively, when the prevailing wind changed and came from the BTH region. In addition, minimum deviation of the source apportionments from PMF results and 14C measurement was used as the optimal choice of the model exercises. Here, two minor overestimations with the same range (3 %) suggested that the PMF results provided a reasonable source apportionment of regional PM2.5 in the North China during winter. Based on the results above, eight main sources were identified, of which, coal combustion, biomass burning and vehicle emissions were the largest contributors of PM2.5, accounting for 29.6 %, 19.3 % and 15.8 %, respectively. Compared with the overall source apportionment, the contribution of vehicle emission increased slightly when air masses came from the BTH region, the contribution of mineral dust and coal combustion rose obviously when air masses were from the Mongolia with high speed, and biomass burning became the dominant contributor when air masses carried from the Shandong Peninsula. As the largest contributor to PM2.5 in winter of North China, coal combustion has been identified as the most leading emission sector to be controlled for improving the air quality by the government. Vehicle emission contributed significantly to the PM2.5 levels in the BTH region, which has also been considered to control as the second major emission sector. Biomass burning emission was highlighted in the present study because of its dominant contribution to PM2.5 burden in the Shandong Peninsula. Some suggests were provided to wake farmers from agricultural residue burning in household and field.