Revealing the discrepancy in potential driving factors of particulate-bound mercury between urban and suburban sites in a southeast asian megacity using generalized additive model

Abstract

Particulate-bound mercury (PBM) plays a critical role in atmospheric mercury (Hg) cycling, yet its complex spatiotemporal variability and potential driving factors remain insufficiently understood, particularly in the Southeast Asia (SEA) region. This study reported year-round (May 2022 to April 2023) data of PBM at an urban (Nguyen Van Cu: 59.81 ± 29.15 pg m-3) and a suburban site (Can Gio: 26.4 ± 9.59 pg m-3) in southern Vietnam. Distinct seasonal trends were observed at both sites, with elevated PBM concentrations in the dry season (November-February), likely driven by changes in source origin and transport paths of air masses. Lower PBM concentrations in the wet season (July-September) may result from enhanced removal by wet deposition, whereas limited rainfall in the dry season reduces this effect, leading to higher concentrations. We employed Generalized Additive Models (GAM), which effectively captured nonlinear relationships between PBM and meteorological-chemical covariates. GAMs explained 87.7% of PBM variance in the urban area and 41.6% in the suburban area, indicating better model performance in urban vs suburban areas. In the urban area, metals (i.e. Cr, Sr, Pb, and V) were the dominant contributors (36.7%), suggesting influence from industrial and traffic-related sources. In contrast, PBM at the suburban site was mainly modulated by temperature (60.8%), Zn (21.3%), and planetary boundary layer height (17.9%), pointing to the significance of atmospheric processes over local emissions. Our findings highlight the utility of GAM in resolving complex PBM-environment interactions and indicate its potential for advancing source attribution and informing targeted mercury mitigation strategies.