In-situ measurement of secondary aerosol formation potential using a flow reactor: Livestock agricultural area

Atmospheric ammonia (NH₃) is an important particulate matter (PM) precursor. The primary sources of ammonia in agriculture are livestock farming and synthetic fertilizers. Here, an oxidation flow reactor (OFR) was deployed in the vicinity of livestock farming during the summer of 2020 and winter of 2021 to determine the extent of secondary aerosol formation. The OFR was run in a 1-h cycle of different aging times for the daytime and nighttime oxidants of OH and NO₃ radicals, respectively. The daytime reaction periods were 05:00–20:00 and 08:00–18:00, respectively, for summer and winter. Ambient and aged PM2.5 were characterized for secondary aerosol formation potential (AFP) using a time-of-flight aerosol chemical speciation monitor (ToF-ACSM). Ambient PM2.5 mean composition during summer was dominated in the order of nitrate (41%), organic matter (33%), ammonium (15%), and sulfate (11%). Secondary AFP was in the higher order, nitrate (71%), ammonium (20%), organic matter (8%), and sulfate (1%). A prominent effect of NH₃ was observed when the primary aerosol was aged at high NO_x and relative humidity (RH). Source apportionment revealed secondary organic aerosol (SOA)-dominant organic aerosols.