Mechanisms of haze influencing phase distribution and human exposure to airborne flame retardants with different uses: Emission, partition, and dry deposition

This study elucidated the mechanisms governing variations in the occurrence and human exposure to flame retardants (FRs) with diverse applications on haze days. The high atmospheric stability on haze days converts the atmospheric environment into a closed system, where local emissions (LM), gas-to-particle transport (GPT), and dry deposition of particles (DP) determine the fate and destination of FRs. When LM < GPT and DP, FRs are removed by DP, thereby decreasing human exposure. Conversely, when LM ≈ GPT and DP, the increase in airborne particles on haze days only affects occurrences and human exposure to FRs with gas-particle partitioning quotient (log K_P) ranging from −3.95 to −1.45. We also analysed three types of FRs in 198 size-segregated particulate samples and 22 gaseous samples collected on non-haze and haze days in a Chinese city where haze frequently occurs. This study validated the aforementioned mechanisms and fundamentally accounted for the decreased levels of polybrominated diphenyl ethers (PBDEs) in skin-wipe samples on haze days in other published studies. These results suggest that haze has diverse influences on human exposure to FRs and provide a new basis for a comprehensive understanding of the health effects of haze.