Oxidative potential of PM_2.5 in Guangzhou, Southern China: Source apportionment and association with airborne...

Oxidative potential (OP) can be used as an indicator of the health risks of particulate matter in the air. To study the variation and sources of OP, we conducted an observation of PM_2.5 in a megacity in southern China in winter and spring of 2021. The results show that the average concentration of PM_2.5 decreased by 47 % from winter to spring, while volume-normalized and mass-normalized OP (i.e., OP_v and OP_m) increased by 6 % and 69 %, respectively. It suggests that the decline of PM_2.5 may not necessarily decrease the health risks and the intrinsic toxicity of PM_2.5. Variations of OP_v and OP_m among different periods were related to the different source contributions and environmental conditions. The positive matrix factorization model was used to identify the major sources of OP_v. OP_v was mainly contributed by biomass burning/industrial emissions (29 %), soil/road dust (20 %), secondary sulfate (14 %), and coal combustion (13 %) in winter. Different major sources were resolved to be secondary sulfate (36 %), biological sources (21 %), and marine vessels (20 %) in spring, presenting the substantial contribution of biological sources. The analysis shows strong associations between OP_v and both live and dead bacteria, further confirming the important contribution of bioaerosols to the enhancement of OP. This study highlights the importance of understanding OP in ambient PM_2.5 in terms of public health impact and provides a new insight into the biological contribution to OP.