The Elemental Characteristics and Human Health Risk of PM 2.5 during Haze Episode and Non-Haze Episode in Chiang Rai Province, Thailand.

Fine particle matter (PM 2.5 ) was directly related to seasonal weather, and has become the influencing factor of air quality that is harmful for human health in Chiang Rai province. The aims were determining the elemental composition in PM 2.5 and human health risk in haze (March 2021) and non-haze episodes (July-August 2021). Nine elements in PM 2.5 were measured by using an Atomic Absorption Spectrophotometer, and an enrichment factor was used to identify the emission source. The results showed that the average concentration of PM 2.5 was 63.07 μg/m 3 in haze episodes, and 25.00 μg/m 3 in a non-haze episode. The maximum concentration was 116.7 μg/m 3 in March. The majority of elements originated from anthropogenic sources. In haze episodes, PM 2.5 mean concentration was approximately 4.2 times that of the WHO guidelines (15 μg/m 3 24 h), and 1.3 times that of the Thai Ambient Air Quality Standard (50 μg/m 3 ). The analysis of backward air mass trajectory showed that transboundary and local sources significantly influenced PM 2.5 at the monitoring site in the sampling period. In the health risk assessment, the non-carcinogenic risk of Cd was the highest, with a Hazard Quotient (HQ) of 0.048, and the cancer risk of Cr was classified as the highest cancer risk, with the values of 1.29 × 10 -5 , higher than the minimum acceptable level.