Temperature Effects on Secondary Organic Aerosol Formation and Properties

Abstract:

Formation and properties of multiple secondary organic aerosol (SOA) systems were studied in the UC Riverside / CE-CERT dual 90m³ environmental chambers at temperatures ranging from 278K to 313K, controlled to a set point within ±0.5K. Three SOA systems were studied: a simple cyclohexene ozonolysis system, a biogenic α-pinene ozonolysis system, and an anthropogenic gasoline vehicle exhaust. Aerosol number, volume, and mass concentrations were monitored throughout experiments along with particle density, volatility, and hygroscopicity. Both gas and aerosol phase mass spectra were observed in real time via a SYFT selected ion flow tube mass spectrometer (SIFT-MS) and an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), respectively. It was found that the temperature of the system drastically affected aerosol yields in all three systems studied with 278K yields being drastically higher than yields at 313K. Particle density was found to be much higher at 278K for the cyclohexene-O3 and vehicle exhaust systems (at 1.6g/cm³ and 2 g/cm³, respectively), compared to average SOA density of 1.4g/cm³, while the particle density of the biogenic system remained unaffected by temperature. Aerosol phase mass spectra showed significant oxidation at 313K compared to 278K. This work aims to help elucidate temperature’s effect on gas-particle partitioning and hysteresis effects seen in SOA formation that can be used in emerging atmospheric SOA models.