Evaluation of PM2.5 Components and Source Apportionment at a Rural Site in the Ohio River Valley Region
Hourly average PM2.5, daily average PM2.5 and species concentrations were monitored using a tapered element oscillating microbalance, federal reference method and a speciation sampler, respectively in Athens, OH between March 2004 and November 2005. A comprehensive comparison between the TEOM and the FRM showed that the on an average the TEOM was biased 18 % higher than the FRM. Mass balance closure was determined between the FRM measured mass and the sum of the chemical components of PM2.5. For the study period, the sum of components mass concentration was as much as 4% greater than the FRM measured mass. Acidity ratio analysis showed that the aerosol at Athens was periodically acidic all year round and hence the probability of presence of particle bound water was high. Eight percent of the PM2.5 concentration was unidentified in winter compared to just 2% in summer. Athens experienced maximum average PM2.5 levels during summer and was amongst the top three of six sites in Ohio in terms of average PM2.5 concentration for all the four seasons. A clear weekly trend emerged for the urban site with the weekday PM2.5 concentration exceeding the weekend concentration by at least 1.2 µg/m3. The PM2.5 levels in Athens are governed primarily by regional transport and meteorology. PM2.5 samples collected on filters between March 2004 and November 2005 were chemically analyzed and positive matrix factorization was applied to this speciation data to identify the probable sources. PMF arrived at a seven source model to most accurately quantify the PM2.5 observed at Athens. Conditional Probability Function was applied to the identified sources to catalog the local sources. Potential source contribution function was then applied to the apportioned sources to determine the geographical location of these sources. Secondary sulfate source dominated the contributions with a total contribution of 62.6 % with the primary and secondary organic source following second with 19.9%. Secondary nitrate contributed a total of 6.5% with the steel production source and Pb- and Zn-source coming in at 3.1% and 2.9% respectively. Crustal and mobile sources were small contributors (2.5% each) of PM2.5 to the Athens region. The secondary sulfate, secondary organic and nitrate portrayed a clear seasonal nature with the sulfate and secondary organic peaking in summer and the nitrate reaching a high in winter. The unexpectedly high percentage of secondary sulfate observed at a rural site like Athens suggests the involvement of long range transport mechanisms. Trajectory regression analysis was conducted using sulfate source contribution data and the results indicated that the Ohio River Valley region was the primary contributor to the secondary sulfate at Athens.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:pm2 5 positive matrix factorization potential source contribution function trajectory regression analysis conditional probability
Date of Publication:01/01/2007