Impact of local traffic exclusion on near-road air quality: Findings from the New York City “Summer Streets” campaign

We monitored curbside airborne particulate matter (PM) concentrations and its proinflammatory capacity during 3 weekends when vehicle traffic was excluded from Park. Ave., New York City. Fine PM concentration peaked in the morning regardless of traffic while ultrafine PM was 58% lower during mornings without traffic. Ultrafine PM concentration varied linearly with traffic flow, while fine PM spiked sharply in response to random traffic events that were weakly correlated with the traffic signal cycle. Ultrafine PM concentrations decayed exponentially with distance from a cross street with unrestricted traffic flow, reaching background levels within 100 m of the source. IL-6 induction was typically highest on Friday afternoons but showed no clear relationship to the presence of traffic. The coarse fraction (>2.5 μm) had the greatest intrinsic inflammatory capacity, suggesting that coarse PM still warrants attention even as the research focus is shifting to nano-particles.

► During a period of traffic exclusion morning PM2.5 concentration remained high.
► Ultrafine concentrations were lower during mornings without traffic.
► While ultrafine PM varied linearly with traffic flow, fine PM was unrelated to flow.
► Ultrafine PM decayed exponentially with distance from a cross street with traffic.
► The coarse fraction (>2.5 mm) had the greatest intrinsic inflammatory capacity.