United States Department of Transportation
i
Investigation of Nitrogen Oxides Emissions from a Major Roadway
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2009-12-31
[PDF-578.30 KB]
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TRIS Online Accession Number:01154222
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Abstract:In this research project, the authors (1) built a mobile nitrogen oxide (NO) and nitrogen dioxide (NO2) measurement unit with the associated weather monitoring instrumentation; (2) obtained coordinated measurements of NO and NO2 concentrations and meteorological conditions at varying distances from the roadway, together with the traffic volume data; (3) used CALINE4 to estimate the NO2 concentrations at receptors located at the measurement points; and (4) analyzed the data obtained to elucidate the adequacy of CALINE4 in predicting the local NO2 concentrations near roadways. Measurements showed that nitrogen oxides (NOx) concentration decreases rapidly with the distance from the roadway and drops from 25.4 ppb to a value around 8.3 ppb, which remains fairly constant for distances greater than about 150 m from the I-64 median. The reason for this decrease is atmospheric dispersion and conversion of NOx to other nitrogen containing compounds. Close to the roadway (less than about 100 m from the I-64 median), the majority of NOx is NO, which converts to NO2 and other nitrogen compounds and falls from 17.3 to a value about 3.4 ppb at distances greater than 150 m from the median. The decrease in NO2 concentration is not as much and falls from about 12 ppb at 74 m to about 5.5 ppb beyond 150 m. This may be due to the conversion of some NO to NO2 possibly through its reaction with ozone. Close to the roadway, there was significant variation in the measured NO and NOx concentrations due to the effects of emissions coming from individual vehicles passing close to the analyzer intake. This effect became less significant at larger distances from the roadway. The NO2 concentrations at the receptor locations were predicted using CALINE4, which can provide estimates with a sensitivity of ± 5 ppb. Since the measured NO2 concentrations were between 5 and 15 ppb, CALINE4 was expected to predict 0.010 ppm NO2 at each receptor location. As expected, the predicted NO2 concentrations at receptors beyond 100 m of the I-64 median were 0.01 ppm. CALINE4 also correctly predicted 0.01 ppm NO2 at the first receptor location, which had a measured value of 0.012 ppm. These observations indicate that the current data cannot provide an adequate evaluation of the CALINE4 program. To obtain a reasonable evaluation, data are needed during the rush hour traffic and closer to the roadway, which are expected to give higher NO2 concentrations.
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