Integrating nephelometer measurements for the airborne fine particulate matter (PM 2.5) mass concentrations

Abstract

This work describes the application of integrating nephelometer measurements for the determination of airborne fine particulate matter (PM 2.5) mass concentrations. In response to over 150 complaints (spanning a period of 20 years) from local citizens of irritant fogs and pungent odors, the North Carolina Division of Air Quality conducted a monitoring program, in collaboration with the Washington Regional Air Quality Office and PCS Phosphate, Inc., to characterize air quality in the Pamlico River airshed of eastern North Carolina. The continuous monitoring from 1 May through 31 October 2000 at four sites, involved collection of air samples and subsequent quantification for reactive acidic and basic gases, aerosols and fine particulate matter (PM 2.5) using a 7-day Annular Denuder System (ADS). Additionally, the airborne concentration of the fine particulate matter (PM 2.5) was concurrently (to the ADS) monitored using a tapered element oscillating micro-balance (TEOM). Relevant meteorological data were obtained from conventional sensors installed at each sampling site. An integrating nephelometer was used for the regional visibility measurements. An integrating nephelometer was used to measure light scattering (a surrogate for visibility) continuously for 24-h per day over a 6-month period at the four sites. A linear relationship has been found for the nephelometer (Beta scat) measurements and mass data (PM 2.5) obtained both from the TEOM and ADS. The calculated correlation coefficient results between nephelometer and ADS and nephelometer and TEOM are satisfactory and close to one. This indicates that in this region, the nephelometer measurements have the potential to be a surrogate for the determination of regional airborne fine particle (PM 2.5) mass concentrations. The ratios for each of the four sampling sites using 24-h averages of nephelometer data and PM 2.5 concentrations from the ADS units and the TEOM gave an average ratio of 0.32±0.02. This value implies that the physical properties of the fine particulate (PM 2.5) mass at each of the four sites were similar. The precision of nephelometer measurements (as Beta scat) has been demonstrated by collocating three nepehlometers for continuous 24-h measurements for 10 days at one of the four sampling sites. Percent difference among the three instruments ranged from 0.42% to 4.41% and the inter-correlation produced R 2 values of 0.9833, 0.9874 and 0.9943, respectively. This study results demonstrates that the integrating nephelometer is a simple, inexpensive and a sensitive instrument that can be used in field studies. Furthermore, data on both light scattering (for visibility) and fine particulate (PM 2.5) mass concentrations can be obtained reliably and importantly in a time effective manner for a rapid assessment of fine particle (PM 2.5) air pollution.