Chlorine radicals (·Cl) initiated amine oxidation plays an important role for the formation of carcinogenic nitrosamine in the atmosphere. Piperazine (PZ) is considered as a potential atmospheric pollutant since it is an alternative solvent to monoethanolamine (MEA), a benchmark solvent in a leading CO2 capture technology. Here, we employed quantum chemical methods and kinetics modeling to investigate ·Cl-initiated atmospheric oxidation of PZ, particularly concerning the potential of PZ to form nitrosamine compared to MEA. Results showed that the ·Cl-initiated PZ reaction exclusively leads to N-center radicals (PZ-N) that mainly react with NO to produce nitrosamine in their further reaction with O2/NO. Together with the PZ + ·OH reaction, the PZ-N yield from PZ oxidation is still lower than that of the corresponding MEA reactions. However, the nitrosamine yield of PZ is higher than the reported value for MEA when [NO] is <5 ppb, a concentration commonly encountered in a polluted urban atmosphere. The unexpected high nitrosamine yield from PZ compared to MEA results from a more favorable reaction of N-center radicals with NO compared to O2. These findings show that the yield of N-center radicals cannot directly be used as a metric for the yield of the corresponding carcinogenic nitrosamine.
BACKGROUND AND AIM: We aimed to assess the integrated and time-resolved personal, household, and community PM₂.₅ exposure patterns associated with different cooking and heating fuels and other key characteristics in rural and urban China. METHOD: The CKB-Air study involved parallel measurements of personal, household, and community PM₂.₅ in summer (MAY-SEP 2017) and winter (NOV 2017-JAN 2018) in ~380 participants from one urban and two rural communities in China, with ~61,000-81,000 person-hours of data across different locations after data cleaning. Age- and sex-adjusted geometric means of PM₂.₅ were calculated, by key participant characteristics overall and by season. Spearman correlation coefficients between PM₂.₅ levels across different locations were computed. RESULTS: Solid fuel users had ~90% higher personal and kitchen 24-hour average PM₂.₅ exposure than clean fuel users or those who did not cook or heat. They also had a more substantial increase (~75%) in personal and household PM₂.₅ in winter (versus summer) compared to other participants (~20%), whereas community levels were 2-3 times higher in winter regardless of fuel use. Overall, solid fuel users had markedly higher weighted annual average PM₂.₅ exposure (personal: 77.8 [71.1-85.2] µg/m³, ~90% higher; kitchen: 103.7 [91.5-117.6] µg/m³, ~130% higher; living room (62.0 [57.1-67.4] µg/m³, ~65% higher) than clean fuel users. There was a remarkable diurnal variability in PM₂.₅ exposure among the participants, with 5-minute moving average 700-1,200µg/m³ in typical meal times. Personal PM₂.₅ was moderately correlated with living room (Spearman r: 0.64-0.66) and kitchen (0.52-0.59) levels, but only weakly correlated with community levels, especially in summer (r_summer_range: 0.15-0.34) and among solid fuel users (r_summer_range: 0.11-0.31). CONCLUSIONS: Solid fuel use for cooking and heating was associated with estimated annual personal and household PM₂.₅ exposure levels at 15-20 times the WHO Air Quality Guideline. Household PM₂.₅ was a better proxy of personal exposure than community PM₂.₅ in this setting.
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