The pollution levels, var iation character istics, sources and implications of atmospheric carbonyls in a typical rural area of North China Plain during winter

Atmospheric carbonyls were measured at a typical rural area of the North China Plain(NCP)from November 13 to December 24,2017 to investigate the pollution characteristics,sources and environmental implications.Fifteen carbonyls were detected,and formaldehyde,acetaldehyde and acetone accounted for about 81% at most.The concentration of the total carbonyls in heavily polluted days was twice more than that in clean days.In contrast to other carbonyls,m-tolualdehyde exhibited relatively high concentrations in the clean days in comparison with the polluted days.The ratios of three principal carbonyls to CO showed similar daily variations at different pollution levels with significant daytime peaks.Multiple linear regression analysis revealed that the contributions of background,primary and secondary sources to three principal carbonyls showed similar variation trends from the clean level to the heavily polluted level.The OH formation rate of formaldehyde showed a similar variation trend to its photodegradation rate,reaching the peak value at noon,which is important to maintain relatively high OH levels to initiate the oxidation of various gas-phase pollutants for secondary pollutant formation at the rural site.OH radical consumption rate and ozone formation potential(OFP) calculations showed that formaldehyde and acetaldehyde were the dominant oxidative species among measured carbonyls.As for OH radical consumption,n-butyraldehyde and m-tolualdehyde were important contributors,while for ozone formation potential,n-butyraldehyde and propionaldehyde made significant contributions.In addition,the contribution of carbonyl compounds to secondary organic aerosol(SOA) formation was also important and needs further investigation.