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FIELD METHOD COMPARISON BETWEEN PASSIVE AIR SAMPLERS AND CONTINUOUS MONITORS FOR VOLATILE ORGANIC COMPOUNDS AND NO2 IN EL PASO, TEXAS, USA
Citation:
Mukerjee, S, L. Smith, G A. Norris, M. T. Morandi, M Gonzales, C. A. Noble, L Neas, AND A H. Ozkaynak. FIELD METHOD COMPARISON BETWEEN PASSIVE AIR SAMPLERS AND CONTINUOUS MONITORS FOR VOLATILE ORGANIC COMPOUNDS AND NO2 IN EL PASO, TEXAS, USA. JOURNAL OF AIR & WASTE MANAGEMENT ASSOCIATION 54(3):307-319, (2004).
Impact/Purpose:
Overall Goal: To develop spatial analyses using limited network-based air quality and GIS and other ancillary spatial information to estimate exposures for epidemiologic studies.
Goal of NERL Contribution: To develop regression-based spatial models using said measures and ancillary information to predict such exposures at unmonitored locations.
Specific Objectives:
1. To determine whether ultrafine (<0.1 um), accumulation (0.1-0.7), and/or coarse (1-10 um) mode particle counts correlate with CO, NO2 and VOCs emitted from mobile and/or other urban sources using source apportionment modeling techniques.
2. To determine spatial associations among measured levels of NO2, VOCs, and (possibly) ultrafine/accumulation/coarse mode particle counts from mobile and other urban sources in El Paso. Spatial variability in ultrafine/accumulation/coarse mode particle concentrations will be determined using available PM, NO2, VOC and available surrogates of motor vehicle emissions. These measured or predicted spatial associations will then be used by NHEERL to ultimately assess impact of these particle counts and gaseous species on children's exposures in schools.
3. To evaluate accuracy of NO2 and VOC measurements using the passive badges to be deployed by EPA versus collocated FRM devices established by the State of Texas. In addition, to evaluate precision of collocated NO2 and VOC passive badge measurements.
4. To use spatial analysis concepts to evaluate their possible application in an EPA Region 6 study entitled "Air Toxics Data and Analysis and Development of a Predictive Model of Estimation of Ambient Vocs in Selected Census Tracts in Houston-Galveston, TX."
Description:
Passive sampling of gas-phase air toxics and criteria pollutants has become an attractive monitoring method in human exposure studies due to the relatively low sampling cost and ease of use. This study evaluates the performance of Model 3300 Ogawa(TM) Passive NO2 Samplers and 3M(TM) 3520 Organic Vapor Monitors (OVMs) by comparing the integrated passive sampling concentrations to averaged hourly NO2 and VOC measurements made at two continuous air monitoring stations (CAMS) operated by the Texas Commission on Environmental Quality (TCEQ) in the U.S.-Mexico border city of El Paso, Texas. Passive samplers were deployed over three time intervals (3 day weekend, 4 day weekday, and 7 day weekly) for three consecutive weeks, from November 29, 1999 through December 17, 1999. OVM concentrations were corrected for ambient pressure to account for the higher elevation in El Paso. Highly precise results (< 5 % relative standard deviation, RSD) were found for NO2 measurements from collocated Ogawa samplers. Reproducibility was lower from duplicate OVMs for the BTEX (benzene, toluene, ethylbenzene, and xylene isomers) VOC species (>/- 7 % RSD for 2 day samples) with better precision for longer sampling periods. Comparison of Ogawa N02 samplers with chemiluminescence measurements averaged over the same time period suggested potential calibration problems with the chemiluminescence analyzer at the sites, although further evaluation of the Ogawa sampler with continuous measurements was considered necessary. For the BTEX species compared, generally good agreement was obtained between OVMs and auto-GC measurements. The OVMs successfully tracked increasing levels of organic pollutants recorded by the continuous monitors. However, except for toluene, the OVM BTEX measurements generally exceeded their continuous counterparts with a mean bias ranging from 5-10 %. Although the interpretation of the study results was limited due to small sample sizes, diffusion barrier influences due to the design of the shelters, used to house the OVMs, and differences in sampling heights between OVMs and the auto-GC inlet may explain the over-estimation. This study demonstrates the need to perform additional evaluation of collocated passive samplers/with continuous monitors and/or other pumped sampling methods to further evaluate the precision and sampling rate.
The U.S. EPA through its Office of Research and Development funded and managed the research described here under contract 68-D-99-012 to Research Triangle Institute and contract 68-D0-0206 to ManTech Environmental Technology, Inc. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.