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

This study addresses three objectives: (1) to assess the correlation of NO 2 to other ambient pollutants measured with passive samplers; (2) to explore peak traffic particulate matter air pollution correlations with passively measured NO 2; and (3) to pilot an advanced mobile air pollution laboratory to supply supplementary information on correlations between NO 2 and other air pollutants. Active and passive monitoring was conducted at two transects perpendicular to an expressway with nearly 400,000 vehicles per day. NO 2, NO x , O 3, 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. Levels of NO 2 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 NO 2 measurements and passive NO x , O 3 ( 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 NO 2 and VOCs were more variable. Active measurements of NO 2 and PM 2.5, ultrafine particles, O 3 and black carbon, had high correlations ( r∼0.7–0.96). The variability of many traffic-related pollutants around an expressway is characterized well by passive measurements of NO 2. Further research is needed to assess whether these relationships hold in different traffic and land-use environments.