Indoor-outdoor Relationships and Source Apportionment of Fine Particulate Matter (PM2.5) in Retirement Communities of the Los Angeles Basin

摘要

Concurrent indoor and outdoor measurements of PM2.5 were conducted at three retirement homes in the Los Angeles Basin during two separate seasons between 2005 and 2006. Indoor-to-outdoor (I/O) mass ratios and correlation coefficients of PM2.5 chemical constituents were calculated to determine the influence of outdoor and indoor sources on PM2.5 levels inside the retirement homes. Elemental carbon (EC), a tracer of diesel emissions, displayed very high I/O ratios accompanied by strong I/O correlations, indicating the significant impact of outdoor sources on indoor levels of EC. Likewise, indoor concentrations of metals and trace elements were found to be significantly affected by outdoor sources. Indoor levels of PAHs, hopanes and steranes were generally strongly correlated with their outdoor components and displayed I/O ratios close to unity. On the other hand, concentrations of n-alkanes and organic acids inside the retirement communities were dominated by indoor sources, as indicated by their I/O ratios, which exceeded unity. Source apportionment analysis, which was conducted by means of a molecular-marker chemical mass balance model, revealed that vehicular sources were the major contributor to both indoor and outdoor PM2.5, respectively accounting for 39 and 46% of total mass. Moreover, the contribution of vehicular sources to indoor levels was generally comparable to their corresponding outdoor estimates, illustrating the strong influence of these sources on indoor PM2.5. "Other water-insoluble organic matter", which accounts for the emissions from uncharacterized primary biogenic sources, displayed a wide range of contribution from 2 to 73% of PM2.5, across all sites. Lastly, higher indoor than outdoor contribution of "other water-soluble organic matter" was evident at some of the sites, suggesting the production of secondary aerosols as well as emissions from primary sources, including cleaning or other consumer products, at indoor environments.