Particle count and black carbon measurements at schools in Las Vegas, NV and in the greater Salt Lake City, UT area.

As part of two separate studies aimed to characterize ambient pollutant concentrations at schools in urban areas, we compare black carbon and particle count measurements at Adcock Elementary in Las Vegas, NV (April-June 2013), and Hunter High School in the West Valley City area of greater Salt Lake City, UT (February 2012). Both schools are in urban environments, but Adcock Elementary is next to the U.S. 95 freeway. Black carbon (BC) concentrations were 13% higher at Adcock compared to Hunter, while particle count concentrations were 60% higher. When wind speeds were low-less than 2 m/sec-both BC and particle count concentrations were significantly higher at Adcock, while concentrations at Hunter did not have as strong a variation with wind speed. When wind speeds were less than 2 m/sec, emissions from the adjacent freeway greatly affected concentrations at Adcock, regardless of wind direction. At both sites, BC and particle count concentrations peaked in the morning during commute hours. At Adcock, particle count also peaked during midday or early afternoon, when BC was low and conditions were conducive to new particle formation. While this midday peak occurred at Adcock on roughly 45% of the measured days, it occurred on only about 25% of the days at Hunter, since conditions for particle formation (higher solar radiation, lower wind speeds, lower relative humidity) were more conducive at Adcock. Thus, children attending these schools are likely to be exposed to pollution peaks during school drop-off in the morning, when BC and particle count concentrations peak, and often again during lunchtime recess when particle count peaks again.

IMPLICATIONS: Particle count concentrations at two schools were shown to typically be independent of BC or other pollutants. At a school in close proximity to a major freeway, particle count concentrations were high during the midday and when wind speeds were low, regardless of wind direction, showing a large area of effect from roadway emissions even when the school was not downwind of the roadway. At the second school, which sits in an urban neighborhood away from freeways, high particle counts occurred even though solar radiation was low during wintertime conditions, meaning that exposure to high particle counts can occur throughout the year.