HR: 1340h
AN: A23A-0773    [Abstracts]
TI: Weekday/Weekend Differences in Ambient Concentrations of Primary and Secondary Air Pollutants
AU: * Blanchard, C L
EM: cbenvair@pacbell.net
AF: Envair, 526 Cornell Avenue, Albany, CA 94706 United States
AB: We evaluated the differences between mean day-of-week ambient concentrations of ozone precursors, ozone, and other secondary species using 1998-2003 ambient air-pollutant data from monitoring sites in 23 states in New England, the Midwest, the mid-Atlantic, and isolated urban areas in the western and southern U.S. For CO, NO, and NOx, we examined different times and averaging intervals: hourly (6 am and noon), three-hour averages (6-9 am, 9 am-12 noon, 12 noon-3 pm), and nine-hour daytime averages (6 am-3 pm). The median decreases at 6 am and noon bracketed the median daytime (6 am to 3 pm) decreases and closely represented the decreases occurring for the 3-hour averaging times 6 am-9 am and 12 noon-3 pm. In all areas and at both 6 am and noon, substantial declines in ambient concentrations of NO, NO2, and NOx occurred on weekends. Relative to Wednesdays, the median declines in 6 am Sunday ambient NO and NOx levels were 70.6 percent (interquartile [IQ] range 60.3-77.9 percent) and 57.5 percent (IQ range 47.2-63.4 percent), respectively; the median declines of 6 am Saturday NO and NOx levels were 52.7 percent (IQ range 40.8 to 61.8) and 40.1 percent (IQ range 33.0 to 48.1), respectively (204 sites with NO, NO2, and/or NOx). Most decreases were statistically significant (e.g., 173 NO sites, 170 with lower 6 am concentrations on Sundays than on Wednesdays, 153 statistically significant [p$<$0.01] decreases). The median decreases in ambient CO concentrations were smaller than those for NO and NOx. Relative to Wednesdays, the median declines in 6 am ambient CO levels at 227 monitors were 41.5 percent (IQ range 30.6 to 53.0) on Sundays and 28.1 percent (IQ range 20.7 to 36.6) on Saturdays. Most decreases were statistically significant (e.g., 227 sites, 220 with lower 6 am concentrations on Sundays than on Wednesdays, 202 statistically significant [p$<$0.01] decreases). For PAMS hydrocarbon data, day-of-week means were determined for the 9 am-3 pm ambient concentrations of alkanes, alkenes, aromatics, sums of species, and selected compounds. The median Wednesday-Sunday decreases in daytime concentrations of aromatics ranged from 12.4 percent (Baltimore) to 49 percent (Dallas-Fort Worth); the median of the median decreases was 29.7 percent. The median decreases in the sum-of-species ranged from 6.1 to 26.2 percent. For ozone, we determined day-of-week averages for both peak 1-hour and peak 8-hour concentrations. Each peak ozone average was computed in three ways: (1) using all measurements from the months of March through October of each year, (2) using the top three peak ozone days for each day of the week and each year, and (3) using the top ten peak ozone days for each day of the week and each year. Over all 480 ozone monitoring sites, the largest number of weekend ozone increases occurred for peak 8-hour concentrations determined from all monitoring days: these peak ozone levels were 3.4 percent higher (median change) on Sundays than on Wednesdays (IQ range 0.4 to 6.9 percent higher on Sundays; 294 weekend increases, 186 weekend decreases, 8 decreases statistically significant). The largest number of weekend ozone decreases occurred for the peak 1-hour concentrations determined from high-ozone days: median 2 percent lower on Sundays than on Wednesdays (IQ range 2.7 percent Sunday increase to 6.3 percent Sunday decrease; 226 increases, 254 decreases, 22 decreases statistically significant). The relative lack of change in ozone concentrations on weekends, despite the occurrence of substantial and widespread weekend decreases in ambient precursor concentrations, merits further study.
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting