PRINCIPAL COMPONENT ANALYSIS OF SUMMERTIME ORGANIC AEROSOLS AT NIWOT RIDGE, COLORADO

The organic constituents of atmospheric aerosols collected at Niwot Ri dge, Colorado, along with various physical and meteorological data, we re measured during a collaborative field study. Temporal changes in th e composition of samples collected during summertime at Niwot Ridge, a rural site in the Rocky Mountains west of Denver, were studied. Volat ile organic compounds were thermally desorbed from aerosol particles, separated by gas chromatography, and identified by mass spectrometry. For each of 48 2- to 5-hour samples, 18 organic compounds in aerosol p articles, 11 organic and inorganic compounds in the vapor phase, wind direction, and time of day were measured. Relationships among the vari ables were analyzed by principal component analysis in order to examin e the covariations within the data set. The 31 variables are grouped i nto seven factors, and individual compounds, as well as the factors, s erve as molecular markers for biologic and anthropogenic emission sour ces. Elucidation of several distinct associations within both rural an d urban air masses was possible because of the high time resolution ac hieved in the collection and analysis of aerosols. In addition, factor scores were used to illustrate how several organic compounds vary wit h respect to local atmospheric dynamics.