Trends of Ground-Level Ozone in New York City Area during 2007-2017

The spatiotemporal patterns of ground level ozone (O-3) concentrations in the New York City (NYC) metropolitan region for the 2007-2017 period were examined conjointly with local emissions of O-3 precursors and the frequency of wildfires. Daily 8-h and 1-h O-3 and nitric oxide (NO) concentrations were retrieved from the US Environmental Protection Agency (EPA) Air Data. Annual emission inventories for 2008 and 2017 were acquired from EPA National Emissions Inventory (NEI). The number and area burnt by natural and human-ignited wildfires were acquired from the National Interagency Fire Center (NIFC). The highest daily 8-h max O-3 concentrations varied from 90 to 111 parts per billion volume (ppbv) with the highest concentrations measured perimetrically to NYC urban agglomeration. The monthly 8-h max O-3 levels have been declining for most of the peri-urban sites but increasing (from +0.18 to +1.39 ppbv/year) for sites within the urban agglomeration. Slightly higher O-3 concentrations were measured during weekend than those measured during the weekdays in urban sites probably due to reduced O-3 titration by NO. Significant reductions of locally emitted anthropogenic nitrogen oxides (NOx) and volatile organic compounds (VOCs) may have triggered the transition from VOC-limited to NOX-limited conditions, with downwind VOCs sources being critically important. Strong correlations between the monthly 8-h max O-3 concentrations and wildfires in Eastern US were computed. More and destructive wildfires in the region were ignited by lightning for years with moderate and strong La Nina conditions. These findings indicate that climate change may counterbalance current and future gains on O-3 precursor's reductions by amending the VOCs-to-NOx balance.

Automated summary

This study examines the spatiotemporal patterns of ground level ozone (O-3) concentrations in the New York City metropolitan region from 2007 to 2017, taking into account local emissions of O-3 precursors and the frequency of wildfires. The findings suggest that O-3 concentrations are higher in urban areas compared to suburban sites, with a declining trend in monthly O-3 levels. The study also highlights the importance of reducing locally emitted anthropogenic nitrogen oxides (NOx) and volatile organic compounds (VOCs) in order to maintain a VOC-limited environment.