Total suspended particulate (TSP) and particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) sam ples were collected over Xi’an for a 1-yr period to characterize the seasonal variation...

Real time secondary organic aerosol (SOA) density evolution for m-xylene photo-oxidation and α-pinene ozonolysis was obtained using an Aerosol Particle Mass Analyzer (APM)/Scanning Mobility Particle Spectrometer (SMPS) setup, which has been modified to achieve higher transmission of particles and improved sampling frequency. The aerosol density of SOA generated from α-pinene ozonolysis was found to be 1.24 ± 0.03 g/cm³ while the aerosol generated from m-xylene photo-oxidation was determined to be 1.35 ± 0.03 g/cm³. These results confirm the measurement approach from a combined SMPS and Aerodyne Aerosol Mass Spectrometer (AMS) system and are found to be within good agreement with the effective density measurements.

An improved understanding of atmospheric ice nucleating particles (INP), including sources and atmospheric abundance, is needed to advance our understanding of aerosol‐cloud‐climate interactions. This study examines diverse biomass burning events to better constrain our understanding of how fires impact populations of INP. Sampling of prescribed burns and wildfires in Colorado and Georgia, U.S.A., revealed that biomass burning leads to the release of particles that are active as condensation/immersion freezing INP at temperatures from −32 to −12°C. During prescribed burning of wiregrass, up to 64% of INP collected during smoke‐impacted periods were identified as soot particles via electron microscopy analyses. Other carbonaceous types and mineral‐like particles dominated INP collected during wildfires of ponderosa pine forest in Colorado. Total measured n_INP and the excess n_INP associated with smoke‐impacted periods were higher during two wildfires compared to the prescribed burns. Interferences from non‐smoke sources of INP, including long‐range transported mineral dust and local contributions of soils and plant materials lofted from the wildfires themselves, presented challenges in using the observations to develop a smoke‐specific n_INP parameterization. Nevertheless, these field observations suggest that biomass burning may serve as an important source of INP on a regional scale, particularly during time periods that lack other robust sources of INP such as long‐range transported mineral dust.