Spatial and temporal measurements of NO₂ in an urban area using continuous mobile monitoring and passive samplers

Abstract

This paper describes the use of a continuous mobile monitor and passive samplers to estimate the spatial distribution of NO₂ in an urban area for the purpose of siting a continuous monitor to measure population exposure. Monitoring sites were sites selected based on the State and Local Air Monitoring Stations (SLAMS) and National Air Monitoring Station (NAMS) siting criteria required by the U.S. Environmental Protection Agency (U.S. EPA). SLAMS monitoring objectives define scales in which the NO₂ concentration and land use are homogeneous. The SLAMS scales relevant to NO₂ monitoring for NAMS NO₂ monitoring sites are neighborhood (0.5 to 4 km), and urban (several to 50 km). SLAMS siting objectives also define four categories of sites: highest concentration, representative concentration, impacts of major sources, and background sites. Mobile monitoring with a Scintrex LMA-3 luminal monitor was used on a neighborhood scale to measure the NO₂ concentration at sites that covered a large geographical area. Passive samplers were then located at candidate mobile monitoring locations for long-term sampling which covered the neighborhood to the urban scale. These two methods complement each other by combining short-term continuous measurements and integrated long-term measurements which reflect the National Ambient Air Quality Standard for NO₂ which is based on an annual average. The neighborhood site with the highest concentration was not only in the area of highest population density, but was also representative of the larger urban scale. The magnitude of this urban scale is approximately 20 km.