Decadal Trends in Ozone and Ozone Precursors in the Northeastern United States

Abstract:

Cities in the Northeastern region of the United States were plagued with severe ozone pollution in the 20^th century, but have since moved towards compliance with national ozone standards due to a series of policies aimed at reducing ozone precursors in the region. This analysis integrates ground-based, satellite, and air-borne observations to demonstrate how the ozone chemistry in the metropolitan regions in the Northeastern United States has evolved over the past few decades. Observational data is used in conjunction with a box model to determine the precursor species that have most contributed to ozone production in New York City and Essex, MD between 1996-2019. Results demonstrate that regional reductions in NO_x emissions were successful in transitioning these cities into the NO_x-limited regime of ozone production while VOC reductions over the same time period also decreased ozone production at ground-based sites in the Bronx Botanical Gardens, NY and Essex, MD. The analysis identifies the peak ozone production rate as a function of NO2, VOCs and time, and demonstrates that nonlinearities that may lead to ozone becoming worse before it becomes better in areas with severe pollution. This analysis provides context for the past policies implemented in the area that decreased ozone production and future policies needed to help bring these cities into compliance with the national ozone standard.