Factors affecting the particle size of novel condensation aerosols

Factors that control the particle size distribution of solute in propylene glycol (PG) aerosols generated using the capillary aerosol generator (CAG) were investigated. Among these were entrainment airflow conditions, aerosol coagulation and aerosol generation in controlled relative humidity (RH) environments.; In separate studies, bulk airflow and airflow in the "initial" region were altered. Supplying bulk airflow rates of 100, 60 and 30L/min caused aerosol size to increase as a function of decreasing airflow. This effect was attributed to a reduction in turbulent mixing and vapor nucleation rates at lower airflow rates. Changing airflow within the "initial" region produced an increased aerosol particle size as a function of increased airflow obstruction. This effect appeared to be due in part to reductions in turbulent vapor-air admixture and vapor cooling rates, when airflow was obstructed; this may have caused decreased vapor nucleation rates and vapor condensation onto a smaller number of nuclei. Obstructing entrainment airflow allowed aerosol size to be altered from 0.6 to 1.2mum.; The coagulation of CAG aerosols in reservoirs was investigated in flowing air-stream and static air systems. Particle size in flowing air-stream experiments increased with increasing reservoir volume due to the magnitude of aerosol accumulation in the reservoir during sampling. Particle size in static air experiments was determined by the volume of air that aerosol boluses were restricted to, together with the duration of time aerosols were held. Growth rates were inversely proportional to reservoir volume and proportional to the holding time within static air reservoirs. Coagulation in reservoirs allowed aerosol size to be altered from 0.6 to 2.3mum.; To investigate the effects of controlled RH and temperature, CAG aerosols were generated into RH environments of 40, 70 and 96%RH (22°C). Compared to the 40%RH condition, aerosols size increased progressively when generated in 70 and 96%RH air. Growth ratios between the 40 and 96%RH conditions ranged from 1.2 to 1.4 for caffeine in PG aerosols. This increase was attributed to hygroscopic growth that occurred during generation and transit. When the transit time was extended by 1 second, the aerosol growth ratio was lower (1.1) due to greater evaporation.