Field Evaluation of a DustTrak DRX Photometer under Various Indoor and Outdoor Settings

MARTIN BRANIS

Carles University in Prague, Faculty of Science, Institute for Environmental Studies

     Abstract Number: 516
     Last modified: May 13, 2010

Abstract
Nephelometers can be fairly simple and compact instruments with excellent sensitivity and time resolution; however, scattering per unit mass is a strong function of particle size and refractive index. In the present study a newly designed commercial photometer DustTrak DRX (TSI) was tested against a gravimetrical method represented by a cascade impactor (PCIS personal cascade inpactor sampler). The DRX output is PM1, PM2.5, PM4, PM10 and TSP, the PCIS separates the collected aerosol into five classes: below 250 nanometers, 250-500 nanometers, 0.5 to 1 micrometer, 1 to 2.5 micrometers and 2.5 to approximately 10 micrometers in aerodynamic diameter. We collocated the two types of instruments under various indoor and outdoor conditions and calculated the differences of measurements taking into account namely temperature and relative humidity. Our regression analysis showed high correlation coefficients but various slopes and increments between the two methods. Generally, the DustTrak overreports the fine PM gravimetric values (below PM2.5) and underreports the coarse fractions (over PM10). Higher overestimation was found for higher relative humidity and/or for lower temperature conditions. This suggests that DRX light scattering readings should be calibrated separately for coarse and fine aerosol and that microclimatic factors should be taken into account as well. However, very high correlation coefficients between gravimetrical and light scattering methods (in some instances reaching almost unity) argue that such calibration is possible and that real time photometers such as the DRX are very good complements to PM size resolved mass measurements. They offer invaluable information about short term changes in aerosol concentrations which cannot be obtained during the usual long (24-hour) periods of integrated filter exposure.