Seasonal and Annual Source Appointment of Carbonaceous Ultrafine Particulate Matter (PM_0.1) in Polluted California Cities

Abstract

Samples of ultrafine particle matter mass (PM_0.1) were collected over 12 months at three cities in California: Los Angeles, East Oakland, San Pablo, and over six months at Fresno. Molecular markers adjusted for volatility and reactivity were used to calculate PM_0.1 source contributions. Wood burning was a significant source of PM_0.1 organic carbon (OC) during the winter months in northern California (17-47%) but made smaller contributions in other months (0-8%) and was minor in all seasons in Los Angeles (0-5%), except December (17%) during holiday celebrations. Meat cooking was the largest source of PM_0.1 OC across all sites (13-29%), followed by gasoline combustion (7-21%). Motor oil and diesel fuel combustion made smaller contributions to PM_0.1 OC (3-10% and 3-7%, respectively). Unresolved sources accounted for 22-56% of the PM_0.1 OC. The lack of a clear seasonal profile for this unresolved OC suggests that it may be a primary source rather than secondary organic aerosol (SOA). PM_0.1 elemental carbon (EC) was dominated by diesel fuel combustion with less than 15% contribution from other sources. All sources besides wood smoke exhibited relatively constant seasonal source contributions to PM_0.1 OC reflecting approximately constant emissions over the annual cycle. Annual-average source contributions to PM_0.1 OC calculated with traditional molecular markers were similar to the source contributions calculated with the modified molecular markers that account for volatility and reactivity.