[Characteristics and Sources of PM and Its Light-scattering Properties with Different Chemical Compositions in Urban Area of Beijing].

In recent years, the concentration of PM in the Beijing urban area has decreased with the increase in the proportion of secondary inorganic ions. In order to explore the characteristics and sources of the light scattering of PM with different chemical compositions, PM with its chemical components and scattering coefficient were continuously measured at hourly resolution in the Beijing urban area from December 2020 to November 2021. The components, scattering characteristics, and sources of PM were analyzed. The results showed that NO was the major component of PM in the Beijing urban area, and the (NO) and (SNA) were 24% and 46% in PM, respectively. PM could be divided into six types according to mass concentration and component proportion. The occurrence frequency of the good-type was the highest during the study with a similar duration in the four seasons, and the (SNA), (OM), and (FS) were 32%, 32%, and 28% in PM, respectively. The dust(D)-type and the OM(O)-type appeared mainly in spring and summer with the lowest frequency during the study. FS and OM were their major components, and the (FS) and (OM) were 66% and 46% in PM, respectively. The OM+SO(OS)-type, OM+NO(ON)-type, and NO(N)-type appeared mainly in the afternoon in summer, in the early morning and morning in winter, and at approximately 07:00 every day in spring. Under the condition of low humidity[relative humidity (RH)<40%], the MSE of N-type PM was the highest (4.3 m·g), and that of D-type PM was the lowest (2.1 m·g), reflecting the high scattering ability of SNA. The MSE increased with relative humidity. Under the condition of high humidity (RH>80%), the MSE of all types of PM rose to 1.5 to 1.8 times the values under low humidity. The variation trends of SAE showed that particle size increased with the rising of RH level. Under non-high humidity conditions, the scattering coefficients reconstructed by the revised IMPROVE formula fitted well with the measured values at hourly resolution, the correlation coefficients were between 0.81 and 0.97, and the slopes were between 1.00 and 1.21 except for that of D-type. The N-type fitting result was the best. Under high-humidity conditions, the and the slopes were from 0.82 to 0.84 and from 0.48 to 0.53, respectively. The annual was 203.8 Mm, and N-type PM contributed the most, accounting for 53%, in which the large particles of NHNO were the major contributor. of good-type PM was 67.2 Mm, in which small particles of OM were the major contributor. was 1.5 times the annual (dry), whereas the values of SNA were 1.8 to 2.1 times the (dry). The peak value of NO and RH simultaneously appeared around 07:00, resulting in the maximum of NHNO at this time. The peak value of SO and the of (NH)SO mainly appeared at 16:00 and at 04:00, respectively. The diurnal variation curves of OM concentration and were consistent, and the bimodal peaks appeared at 13:00 and 20:00, respectively. In spring and winter, NO, SO and OM mainly came from the plains east of the Taihang Mountains, and their potential source regions were not in any particular place in summer and autumn; the main potential source regions of FS were the northwest areas of Beijing in spring and autumn. The flow with high RH across the south and southeast of the north China plain and the eastern rim of Bohai Sea was likely to increase the weighted potential source contribution factor values of of SNA in this region.