title: Changes in air quality at near-roadway schools after a major freeway expansion in Las Vegas, Nevada.
abstract: Near-roadway ambient black carbon (BC) and carbon monoxide (CO) concentrations were measured at two schools adjacent to a freeway and at an urban background school 2 km from the freeway to determine the change in concentrations attributable to vehicle emissions after the three-lane expansion of U.S. Highway 95 (US 95) in Las Vegas, Nevada. Between summer 2007 and summer 2008, average weekday small-vehicle volume increased by 40% +/- 2% (standard error). Average weekday large-vehicle volume decreased by 17% +/- 5%, due to a downturn in the economy and an associated decline in goods movement. Average vehicle speed increased from 58 to 69 mph, a 16% +/- 1% increase. The authors compared BC and CO concentrations in summer 2007 with those in summer 2008 to understand what effect the expansion of the freeway may have had on ambient concentrations: BC and CO were measured 17 m north of the freeway sound wall, CO was measured 20 m south of the sound wall, and BC was measured at an urban background site 2 km south of the freeway. Between summer 2007 and summer 2008, median BC decreased at the near-road site by 40% +/- 2% and also decreased at the urban background site by 24% +/- 4%, suggesting that much of the change was due to decreases in emissions throughout Las Vegas, rather than only on US 95. CO concentrations decreased by 14% +/- 2% and 10% +/- 3% at the two near-road sites. The decrease in BC concentrations after the expansion is likely due to the decrease in medium- and heavy-duty-vehicle traffic resulting from the economic recession. The decrease in CO concentrations may be a result of improved traffic flow, despite the increase in light-duty-vehicle traffic. Implications: Monitoring of BC and CO at near-road locations in Las Vegas demonstrated the impacts of changes in traffic volume and vehicle speed on near-road concentrations. However, urban-scale declines in concentrations were larger than near-road changes due to the impacts of the economic recession that occurred contemporaneously with the freeway expansion.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Brown
authors.forename: Michael C
authors.initials: MC
authors.lastname: McCarthy
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: DeWinter
authors.forename: David L
authors.initials: DL
authors.lastname: Vaughn
authors.forename: Paul T
authors.initials: PT
authors.lastname: Roberts
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D002248:Carbon Monoxide / Q000737:chemistry; D009505:Nevada; D012574:Schools; D053260:Soot / Q000737:chemistry; D013997:Time Factors; D001335:Vehicle Emissions
chemical_list: D000393:Air Pollutants; D053260:Soot; D001335:Vehicle Emissions; D002248:Carbon Monoxide