Abstract
The 2009 Study of Houston Atmospheric Radical Precursors (SHARP) field campaign had several components that yielded information on the primary vehicular emissions of formaldehyde (HCHO) and nitrous acid (HONO), in addition to many other species. Analysis of HONO measurements at the Moody Tower site in Houston, TX, yielded emission ratios of HONO to the vehicle exhaust tracer species NOx and CO of 14 pptv/ppbv and 2.3 pptv/ppbv, somewhat smaller than recently published results from the Galleria site, although evidence is presented that the Moody Tower values should be upper limits to the true ratios of directly emitted HONO, and are consistent with ratios used in current standard emissions models. Several other Moody Tower emission ratios are presented, in particular a value for HCHO/CO of 2.4 pptv/ppbv. Considering only estimates of random errors, this would be significantly lower than a previous value, though the small sample size and possible systematic differences should be taken into account. Emission factors for CO, NOx, and HCHO, as well as various volatile organic compounds (VOCs), were derived from mobile laboratory measurements both in the Washburn Tunnel and in on-road exhaust plume observations. These two sets of results and others reported in the literature all agree well, and are substantially larger than the CO, NOx, and HCHO emission factors derived from the emission ratios reported from the Galleria site.Implications: Emission factors for the species measured in the various components of the 2009 SHARP campaign in Houston, TX, including HCHO, HONO, CO, CO2, nitrogen oxides, and VOCs, are needed to support regional air quality monitoring. Components of the SHARP campaign measured these species in several different ways, each with their own potential for systematic errors and differences in vehicle fleets sampled. Comparisons between data sets suggest that differences in sampling place and time may result in quite different emission factors, while also showing that different vehicle mixes can yield surprisingly similar emission factors.
Highlights
Rappenglück et al (2013) reported ambient air measurements at the interchange of Interstate 610 and US 59 in the Galleria area of Houston, TX
Since we are most familiar with its characteristics, we focused on the Harvard/Aerodyne continuouswave Tunable Infrared Laser Differential Absorption Spectrometer (Lee et al, 2011a; Lee et al, 2013) measurement, based on HONO line strengths reported by Lee et al (2012)
On any given day the agreement between cw-TILDAS and UH long path absorption photometer (LOPAP) measurements of HONO is no better than seen in the figure, both the good correlation noted earlier and an examination of the entire common measurement period do not support a conclusion of significant systematic bias between the two instruments
Summary
Rappenglück et al (2013) reported ambient air measurements at the interchange of Interstate 610 and US 59 in the Galleria area of Houston, TX. A third subexperiment, Formaldehyde and Olefins from Large Industrial Releases (FLAIR), included several onroad and tunnel measurements of vehicle exhaust emission ratios by the Aerodyne Mobile Laboratory, for HCHO and for a wide range of volatile organic compounds (VOCs). These measurement programs all provided information on the primary vehicular emissions of HCHO and HONO, whose photolysis is responsible for much of the HOx radical (OH and HO2) production that initiates ozone formation processes (Rappenglück et al, 2013; Olaguer et al, 2014). Comparison of the roadside observations of Rappenglück et al with those from Moody Tower, which is further away from traffic sources, requires some care, while tunnel measurements have potential for their own artifacts, so examination of all three types of Wormhoudt et al / Journal of the Air & Waste Management Association 65 (2015) 699–706 vehicular emissions measurements for roughly the same time and area can be instructive
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
