Determination of external and internal mixing of organic and inorganic aerosol components from hygroscopic properties of sub micrometer particles during a field study in the lower Fraser Valley

A tandem differential mobility analyzer (TDMA) system was developed to measure particle growth factors over a range of relative humidities from 50-85%. This system was deployed in the Lower Fraser Valley, and data was collected at Golden Ears Provincial Park and Eagle Ridge Mountain during the Pacific 2001 field study. Following humidification, particles either had a single hygroscopic mode or a bimodal distribution with more hygroscopic and less hygroscopic modes. Growth factors for the less hygroscopic mode were found to be consistent throughout the study. Monomodal distributions were the more common result. Their growth factor ranged between that of the less and the more hygroscopic modes. Using observed and calculated growth factors, relative organic and inorganic fractions were estimated. Particles at these sites were largely organic. Organic fractions near unity were found at Golden Ears forest and during rainy days at Eagle Ridge.