title: Deciphering the role of radical precursors during the Second Texas Air Quality Study.
abstract: The Texas Environmental Research Consortium (TERC) funded significant components of the Second Texas Air Quality Study (TexAQS II), including the TexAQS II Radical and Aerosol Measurement Project (TRAMP) and instrumented flights by a Piper Aztec aircraft. These experiments called attention to the role of short-lived radical sources such as formaldehyde (HCHO) and nitrous acid (HONO) in increasing ozone productivity. TRAMP instruments recorded daytime HCHO pulses as large as 32 parts per billion (ppb) originating from upwind industrial activities in the Houston Ship Channel, where in situ surface monitors detected HCHO peaks as large as 52 ppb. Moreover, Ship Channel petrochemical flares were observed to produce plumes of apparent primary HCHO. In one such combustion plume that was depleted of ozone by large emissions of oxides of nitrogen (NOx), the Piper Aztec measured a ratio of HCHO to carbon monoxide (CO) 3 times that of mobile sources. HCHO from uncounted primary sources or ozonolysis of underestimated olefin emissions could significantly increase ozone productivity in Houston beyond previous expectations. Simulations with the CAMx model show that additional emissions of HCHO from industrial flares or mobile sources can increase peak ozone in Houston by up to 30 ppb. Other findings from TexAQS II include significant concentrations of HONO throughout the day, well in excess of current air quality model predictions, with large nocturnal vertical gradients indicating a surface or near-surface source of HONO, and large concentrations of nighttime radicals (approximately30 parts per trillion [ppt] HO2). HONO may be formed heterogeneously on urban canopy or particulate matter surfaces and may be enhanced by organic aerosol of industrial or motor vehicular origin, such as through conversion of nitric acid (HNO3). Additional HONO sources may increase daytime ozone by more than 10 ppb. Improving the representation of primary and secondary HCHO and HONO in air quality models could enhance the simulated effectiveness of control strategies.
authors: Houston Advanced Research Center, The Woodlands, TX 77381, USA. eolaguer@harc.edu
authors: Eduardo P
authors: EP
authors: Olaguer
authors: Bernhard
authors: B
authors: Rappenglück
authors: Barry
authors: B
authors: Lefer
authors: Jochen
authors: J
authors: Stutz
authors: Jack
authors: J
authors: Dibb
authors: Robert
authors: R
authors: Griffin
authors: William H
authors: WH
authors: Brune
authors: Maxwell
authors: M
authors: Shauck
authors: Martin
authors: M
authors: Buhr
authors: Harvey
authors: H
authors: Jeffries
authors: William
authors: W
authors: Vizuete
authors: Joseph P
authors: JP
authors: Pinto
mesh_terms: D000388:Air / Q000032:analysis; D000393:Air Pollutants / Q000737:chemistry*; D004784:Environmental Monitoring; D005557:Formaldehyde / Q000032:analysis*; D005609:Free Radicals / Q000737:chemistry*; D009608:Nitrous Acid / Q000032:analysis*; D010126:Ozone / Q000138:chemical synthesis*; D013781:Texas; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D005609:Free Radicals; D005557:Formaldehyde; D010126:Ozone; D009608:Nitrous Acid