Source Investigation for Ambient PM_2.5 in Indianapolis, IN

The objectives of this study were to identify the sources of the PM _2.5 in Indianapolis, Indiana and estimate their contributions to the total PM _2.5 mass concentrations by analyzing the data from the samples collected at the EPA Speciation Trends Networks (STN) site in Indianapolis, Indiana. Both positive matrix factorization (PMF2) and an expanded factor analysis model were applied. The two methods obtained essentially identical source profiles and contributions, so the results of the simpler method, PMF, are described in the formal text of this paper in detail while the corresponding results provided by the expanded factor analysis model are presented in the supplemental material for this paper. The seven resolved sources are secondary sulfate (40.2%), secondary nitrate (21.9%), gasoline emission (16.6%), diesel emission (7.9%), airborne soil (5.3%), Fe-related industries (4.4%), and Cu-related industries (2.5%). The comparison between two models suggests that PMF coupled with subsequent data analysis methods (such as CPF, PSCF, seasonal variation analysis, and weekday/weekend variation analysis) yields the results that are comparable to those of the expanded factor analysis. The results suggest that such studies of STN data can be used to assist in the development of State Implementation Plans (SIPs) for PM _2.5 .

This work was supported by the Lake Michigan Air Directors' Consortium (LADCO) through a contract to Clarkson University. The results presented here do not necessarily reflect the views of LADCO and no endorsement should be inferred. The authors would like to thank Donna Kenski and Michael Koerber of LADCO for their assistance in identifying the likely particle sources in Indianapolis. The authors also wish to acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport model and READY website (http://www.arl.noaa.gov/ready.html) used in this publication.