Correlation of nitrogen dioxide with other traffic pollutants near a major expressway

Objectives This study addresses three objectives: (1) to assess the correlation of NO2 to other ambient pollutants measured with passive samplers; (2) to explore peak traffic particulate matter air pollution correlations with passively measured NO2; and (3) to pilot an advanced mobile air pollution laboratory to supply supplementary information on correlations between NO2 and other air pollutants. Methods Active and passive monitoring was conducted at two transects perpendicular to an expressway with nearly 400,000 vehicles per day. NO2, NOx, O3, VOCs, fine-particles and ultrafine particles were measured at increasing distance away from the expressway. The measurement equipment included Ogawa, TraceAir and 3 M organic vapor monitors (OVM-3500) passive samplers, and an array of active measurement equipment: Dust-Trak and P-Trak monitors, chemoluminescent analyzer, aethalometer, tapered element oscillating microbalance, Grimm condensation particle counter, and an Ionicon analytik proton transfer reaction mass spectrometer. Results Levels of NO2 were observed to decay with increasing distance from the expressway, declining to background levels by 300 m. Moderate to high correlations were observed between passive NO2 measurements and passive NOx, O3 (r 0.60–0.86). The correlations with active PM measurements made with Dust-Trak and P-Trak monitors were in the range 0.64–0.78; correlations between NO2 and VOCs were more variable. Active measurements of NO2 and PM2.5, ultrafine particles, O3 and black carbon, had high correlations (r 0.7–0.96). Discussion The variability of many traffic-related pollutants around an expressway is characterized well by passive measurements of NO2. Further research is needed to assess whether these relationships hold in different traffic and land-use environments.