Source Signatures of Submicron Particle-phase Organic Components at Coastal and Inland California

摘要

Atmospheric submicron particles were collected at a coastal site (La Jolla; 32.87° N, 117.25° W) and an inland site (Bakersfield; 35.35° N, 118.97° W) in California during August 15 - October 1 2009 and May 15 - June 29 2010, respectively. Organic functional group concentrations were quantified by Fourier Transform Infrared (FTIR) spectroscopy and organic fragments were measured using Aerosol Mass Spectrometry (AMS). At the coastal site, organic mass (OM) was dominated (60% of the OM) by fossil fuel combustion sources originating from a heavily polluted area upwind of the site (near the Los Angeles and Long Beach port region), which resulted in a mixture of alkane and carboxylic acid functional groups. The two functional groups varied diurnally in mass and the daytime profiles followed the variations of O3, indicating carboxylic acid groups were formed from ozone-driven reactions. Gas-phase oxidation of alkanes by OH radicals to form dihyfrofuran followed by further ozone reaction of dihydrofuran is the likely acid formation mechanism. Using the multi-day average of the daytime increase of carboxylic acid group concentrations and m/z 44-based AMS Aged Combustion factor, we estimated the lower-bound contributions of secondary organic aerosol (SOA) formed in 12-h daytime of processing in a single day to be 30% of the carboxylic acid groups and 25-50% of the Aged Combustion factor concentration at the coastal site. In contrast, at the inland site, Positive Matrix Factorization (PMF) analyses on the mass-weighed FTIR spectra and the AMS fragment concentrations suggest that the OM consisted primarily of oxygenated organic components, which were also of secondary origin. The inland site also had influence from primary particles from motor vehicular emissions, petroleum operation, and vegetation detritus, which accounted for less than one third of submicron OM.