The process of frost formation has been studied as an important deposition pathway for removing atmospheric pollutants. However, the removal of organic species during frost formation remains unknown. Gas, PM_2.5 and frost samples were collected in Wangdu, a severely polluted rural site in the North China Plain, during the winter of 2018. The concentrations, distributions, sources, and ecological and health risks of the 16 PAHs in the samples were determined. The 24 h-averaged concentrations of PAHs in the air (gas + PM_2.5) reached 719 ng m^-3, indicating that the local atmosphere was heavily contaminated by PAHs in winter. The average concentrations of PAHs in the frost insoluble reached 27.5 μg g^-1, indicating the strong ambient PAHs deposition during the frost process. The distribution patterns of individual PAH species indicated that the PAHs in the gas influenced the frost samples, and the sources of PAHs in frost samples were highly similar to those in PM_2.5 samples. The calculated lifetime lung cancer risk (LLCR) via inhalation of ambient PAHs was classified as high risks. The average total Benzo(a)pyrene toxic equivalent quotient (TEQ) of PAHs in the frost samples was estimated as 2.50 μg TEQ g^-1, posing a high threat to the ecological environment and health. After the melting of frost, the PAHs are released into the soil. Although the concentrations are diluted, the PAH concentrations could adversely affect the growing vegetation or agricultural activities. The extremely high PAH concentrations and their ecological and health risks require special attention and strict regulation.

To better understand the pollution characteristics and formation mechanisms of atmospheric carbonyl compounds, continuous measurements of carbonyl compounds in Jinan were taken for one month at a sampling frequency of 2h. The sources, pollution characteristics, and concentration changes of carbonyl compounds during the summers of 2018 and 2020 were compared. The total concentrations of carbonyl compounds were 10.51±0.13ppbV and 6.30±1.08ppbV in 2018 and 2020, respectively. In both years, formaldehyde, acetone, and acetaldehyde were the major carbonyls. Diurnal variations and correlation analyses showed that exhaust emissions from motor vehicles during peak traffic periods significantly contributed to the concentrations of carbonyl compounds in Jinan, with formaldehyde exhibiting net production. The ratio of formaldehyde/acetaldehyde (C₁/C₂) was 2.64 in 2018 and 2.03 in 2020, indicating that carbonyl compounds are jointly affected by anthropogenic sources and photochemical reactions. Master Chemical Mechanism model analyses showed that the formation of formaldehyde in Jinan was controlled by RO+O₂ reactions, and formaldehyde was mainly consumed via photolysis and its reaction with the hydroxyl radical. In situ photochemistry can further promote formaldehyde production. The comparison of the reactivities of different carbonyl compounds revealed that formaldehyde, acetaldehyde, butyraldehyde, and propionaldehyde play an important role in hydroxyl radical reactions and ozone generation. Among all the measured carbonyl compounds, benzaldehyde contributed the most to secondary organic aerosols (SOAs). Overall, this study provides new insights into the formation mechanisms of carbonyl compounds as well as their pollution characteristics.

The concentration and variation trend of atmospheric carbonyl compounds in Jinan were first measured during autumn 2017 for three continuous weeks at a 3-h time resolution. A total of 14 types of carbonyls were identified, among which acetone, formaldehyde, and acetaldehyde were the most abundant carbonyls and their concentrations were 3.75±2.21 ppbv, 2.65±1.67 ppbv, 1.83±1.17 ppbv, respectively; formaldehyde and acetaldehyde showed similar diurnal variation trends. Butyraldehyde and isovaleraldehyde were another two important carbonyl compounds with concentrations of 1.05±0.59 ppbv and 1.04±0.47 ppbv, respectively. The average C1/C2 ratio was 1.90, which indicated that anthropogenic sources were the main contributor of atmospheric carbonyls. The correlation analysis showed that the measured carbonyls had different sources. Formaldehyde, acetaldehyde, butyraldehyde and isovaleraldehyde were the most important OVOC contributors to ·OH reactivity and O3 formation.