Effects of urban air on cloud condensation nuclei properties

The main research objective was to establish links between air mass properties and cloud condensation nuclei (CCN) concentrations in a suburban environment. The density of the CCN was obtained using a CCN counter located in Beltsville, DC. Supersaturation levels of 0.4, 0.6, 0.8, and 1.0% were considered for analyses. Time series (per month, per day, per supersaturation levels) were established. Trace gas and aerosol chemistry were included in the analyses to establish a link between CCN attributes and air chemistry. Air parcel trajectory analyses were performed to determine the characteristics of CCN based on the air transport history. The study found that the CCN concentrations depended on the origin of the air masses. Low CCN concentrations were associated with maritime air masses, whereas high CCN concentrations were related to continental air masses. The study also found that the size distribution of CCNs shifted to higher diameters with increases in levels of supersaturation, though it became narrower. Sulfates and nitrates dominated the chemical composition of aerosols. These chemical species contributed to experiencing high concentrations of CCN.