Radical Precursors and Related Species from Traffic as Observed and Modeled at an Urban Highway Junction

Bernhard Rappenglueck, Graciela Lubertino, Sergio Alvarez, Julia Golovko, Beata Czader, Luis Ackermann

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Nitrous acid (HONO) and formaldehyde (HCHO) are important precursors for radicals and are believed to favor ozone formation significantly. Traffic emission data for both compounds are scarce and mostly outdated. A better knowledge of today’s HCHO and HONO emissions related to traffic is needed to refine air quality models. Here the authors report results from continuous ambient air measurements taken at a highway junction in Houston, Texas, from July 15 to October 15, 2009. The observational data were compared with emission estimates from currently available mobile emission models (MOBILE6; MOVES [Motor Vehicle Emission Simulator]). Observations indicated a molar carbon monoxide (CO) versus nitrogen oxides (NOx) ratio of 6.01 0.15(r2 ¼ 0.91), which is in agreement with other field studies. Both MOBILE6 and MOVES overestimate this emission ratio by 92% and24%, respectively. For HCHO/CO, an overall slope of 3.14 0.14 g HCHO/kg CO was observed. Whereas MOBILE6 largely underestimates this ratio by 77%, MOVES calculates somewhat higher HCHO/CO ratios (1.87) than MOBILE6, but is still significantly lower than the observed ratio. MOVES shows high HCHO/CO ratios during the early morning hours due to heavy duty diesel off-network emissions. The differences of the modeled CO/NOx and HCHO/CO ratios are largely due to higher NOx and HCHO emissions in MOVES (30% and 57%, respectively, increased from MOBILE6 for 2009), as CO emissions were about the same in both models. The observed HONO/NOx emission ratio is around 0.017 0.0009 kg HONO/kg NOx which is twice as high as in MOVES. The observed NO2/NOx emission ratio is around 0.16 0.01 kg NO2/kg NOx, which is a bit more than 50% higher than in MOVES. MOVES overestimates the CO/CO2 emission ratio by a factor of 3 compared with the observations, which is 0.0033 0.0002 kg CO/kg CO2. This as well as CO/NOx overestimation is coming from light-duty gasoline vehicles.
Original languageEnglish
Article number18
JournalJournal of the Air and Waste Management Association
Volume63
Issue number11
DOIs
Publication statusPublished - 2013

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