Observation and Source Apportionment of Atmospheric Alkaline Gases in Urban Beijing

Alkaline gases, including NH3, C1-3-amines, C1-3- amides, and C1-3-imines, were measured in situ using a water cluster-CIMS in urban Beijing during the wintertime of 2018, with a campaign average of 2.8 +/- 2.0 ppbv, 5.2 +/- 4.3, 101.1 +/- 94.5, and 5.2 +/- 5.4 pptv, respectively. Source apportionment analysis constrained by emission profiles of in-use motor vehicles was performed using a SoFi-PMF software package, and five emission sources were identified as gasoline-powered vehicles (GV), diesel powered vehicles (DV), septic system emission (SS), soil emission (SE), and combustion-related sources (CS). SS was the dominant NH3 source (60.0%), followed by DV (18.6%), SE (13.1%), CS (4.3%), and GV (4.0%). GV and DV were responsible for 69.9 and 85.2% of C1- and C2-amines emissions, respectively. Most of the C3-amines were emitted from nonmotor vehicular sources (SS = 61.3%; SE = 17.8%; CS = 9.1%). DV accounted for 71.9 and 34.1% of C1- and C2-amides emissions, respectively. CS was mainly comprised of amides and imines, likely originating from the pyrolysis of nitrogen-containing compounds. Our results suggested that motor vehicle exhausts can not only contribute to criteria air pollutants emission but also promote new particle formation, which has not been well recognized and considered in current regulations. Urban residential septic system was the predominant contributor to background NH3. Enhanced NH3 emissions from soil and combustion-related sources were the major cause of PM2.5 buildup during the haze events. Combustion-related sources, together with motor vehicles, were responsible for most of the observed amides and imines and may be of public health concern within the vicinity of these sources.

Automated summary

The concentration levels of alkaline gases including NH3, amines, amides, and imines were found to be high during the winter of 2018 in urban Beijing. Source apportionment analysis identified gasoline-powered vehicles, diesel-powered vehicles, septic system emission, soil emission, and combustion-related sources as the main emission sources. Motor vehicle exhausts not only contribute to air pollution but also promote new particle formation. Septic system emission was found to be the main contributor to background NH3, while soil emission and combustion-related sources were the major causes of PM2.5 buildup.