Size distribution of particulate matters (PM) and health risk assessment of PM-bound Polycyclic Aromatic Hydrocarbons in Chiang Mai ambient air

Abstract

Air pollution is one of the major environmental problems in Southeast Asia including Upper Northern Thailand. Sizes of ambient Particulate Matters (PM) are important due to their deposit capability on respiratory system. This study aims to investigate size distribution of atmospheric PM and their polycyclic aromatic hydrocarbons (PAHs) content in urban and rural areas of Chiang Mai Province in relation to traffic and biomass burning sources and to assess human respiratory health risk. Sampling of size fractionated PM (SPM) was conducted in 2019 at urban and rural sites during smoke haze (SH) period (March-April) every 2 days and non-smoke haze (NSH) period (May-June and November) once a month. The SPM samples were continuously collected for 48 hours using eight-stage cascade impactors with a flow rate of 28.3 L/min. SPMs were separated into seven fractions based on aerodynamic particle diameters ranging from 9.0-5.8 um, 5.8-4.7 um, 4.7-3.3 um, 3.3-2.1 um, 2.1 -1.1 um, 1.1-0.65 um, and 0.65-0.43 um. Samples were analyzed for 16-PAHs by GC-MS. The average SPMs (9.0-0.43 um) mass concentrations during SH period were 105.05+29.78 ug/m (urban) and 128.42-39.17 ug/m (rural). Concentration of total PAHs (tPAHs) in SPMs during SH period was obviously higher than the NSH period due to intensive burning. During SH period, average concentration of PAHs in rural area (6.55+2.88 ng/m') was about 1.5 times higher than that of urban area (4.27-1.95 ng/m?), while during NSH period the value of rural area (0.58+0.15 ng/m) was slightly lower than urban area (0.73+0.20 ng/m)) due to suppress of open burning activity and more impact of traffic emission in urban area. PM and PAHs concentrations were highest in the finest particle sizes (0.65-0.43 um) in both periods for both areas. The dominant component of PAHs found during SH period was BbF (23-24% of tPAHs), indicating that open burning was an important source. During NSH period, high ratio of IND, BPER, and DbA were found suggesting traffic emission as a main source in this period. Size distribution patterns of PM and tPAHs were bimodal with a major peak at 0.65-0.43 um and a minor peak at 5.8-4.7 um. High molecular weight PAHs showed a unimodal distribution with the dominant peak found in the finest particle size range. PAHs found in each particle size, were calculated for toxicity equivalent concentrations (TEQ) and inhalation cancer risk (ICR). It was clear that both TEQ and ICR values of PM-bound PAHs in both areas during SH season were high. Moreover, the highest values were corresponded with fine particles (< 2.1 um). It can be concluded that high concentration of fine particles found in ambient air leads to high respiratory health risk.