Daily Trends and Source Apportionment of Ultrafine Participate Mass (PM_(0.1)) over an Annual Cycle in a Typical California City

摘要

Toxicology studies indicate that inhalation of ultrafine particles (D_p ＜ 0.1 μm) causes adverse health effects, presumably due to their large surface area-to-volume ratio that can drive heterogeneous reactions. Epidemiological associations between ultrafine particles and health effects, however, have been difficult to identify due to the lack of appropriate long-term monitoring and exposure data. The majority of the existing ultrafine particle epidemiology studies are based on exposure to particle number, although an independent analysis suggests that ultrafine particle mass (PM_(0.1)) correlates better with particle surface area. More information is needed to characterize PM_(0.1) exposure to fully evaluate the health effects of ultrafine particles using epidemiology. The present study summarizes 1 year of daily PM_(0.1), chemistry and source apportionment at Sacramento, CA, USA. Positive matrix factorization (PMF) was used to resolve PM_(0.1) source contributions from old-technology diesel engines, residential wood burning, rail, regional traffic, and brake wear/ road dust. Diesel PM_(0.1), and total PM_(0.1) concentrations were reduced by 97 and 26%, respectively, as a result of the adoption of cleaner diesel technology. The strong linear correlation between PM_(0.1) and particle surface area in central California suggests that the adoption of clean diesel engines reduced particle surface area by similar amounts. PM_(0.1) sulfate reduction occurred as a result of reduced primary particle surface area available for sulfate condensation. The current study demonstrates the capability of measuring PM_(0.1) source contributions over a 12 month period and identifies the extended benefits of emissions reduction efforts for diesel engines on ambient concentrations of primary and secondary PM_(0.1).