Measurements of the volatility of aerosols from alpha-pinene ozonolysis.

The temperature-dependence of secondary organic aerosol (SOA) concentrations is measured using a temperature-controlled smog chamber. Aerosols are generated from reaction of alpha-pinene (14-150 ppb) and ozone at a constant temperature of 22 +/- 2 degrees C in the presence of the OH-scavenger 2-butanol. After the reactions are completed the chamber is heated or cooled in a range from 20 to 40 degrees C. SOA volume concentrations increase at temperatures below the initial formation temperature and decrease at elevated temperatures. The response to the temperature change as measured by percent mass change per degree ranged from -0.4 to -3.6% K(-1), for a total mass reduction of 5-60% upon heating from 22 to 35 degrees C. The reported range is due to two factors: (1) experimental uncertainty, arising mainly from uncertainty in evaporation and condensation behavior of particles lost to the chamber wall; (2) differences in the temperature response from experiment to experiment. Aerosol temperature sensitivity was also measured by tandem differential mobility analysis (TDMA) where similarly generated SOA were heated from 20 to 25 degrees C to 30-40 degrees C with residence times of 0.5-1.5 min, resulting in particle volume reductions of up to 20%. The TDMA experiments indicate that evaporation of the SOA particles in this system occurs with a potentially significant mass transfer limitation (e.g., accommodation coefficient <0.1).