Evolution of firework-related barium aerosols: insights from single-particle analysis and mass concentration monitoring

Fireworks are a well-known source of barium (Ba) in the atmosphere, yet the aging of firework-derived Ba-containing particles remain poorly understood. Combining online measurements of Ba mass concentrations with single-particle aerosol mass spectrometry (SPAMS) at four sites in Guangzhou, China, we found that firework events raised atmospheric Ba concentrations to levels 1–3 orders of magnitude above background. Peak Ba concentrations varied substantially among sites. Despite its substantially higher population density, the urban-core site under a complete firework ban exhibited a lower peak Ba concentration than a suburban site with time- and location-restricted firework use. This contrast was consistent with a potential mitigating influence of stricter controls, although site-specific emissions and transport may also have contributed. Among the identified particle classes, chloride-rich OClN particles and nitrate-dominated N particles were interpreted as relatively early and more advanced stages of atmospheric aging, respectively. Al/Mg-containing components, were more prevalent in OClN particles than in N particles, consistent with physical mixing during early aging, while several-hour lags between OClN and N peaks and between NO ₂ and particulate NO3- suggested secondary nitrate formation, although primary nitrate emissions from fireworks could not be excluded. These findings provide insights into the rapid aging mechanisms of firework-derived Ba particles and highlight the need to consider differentiated firework-control measures alongside site-specific emission and transport conditions when interpreting spatial pollution contrasts. Screening-level hazard quotients (HQs) based on an oral reference dose (RfD) surrogate were below 1, but short-duration Ba concentration peaks warrant further evaluation of their potential inhalation-related health implications using inhalation-specific toxicity benchmarks.