Long-term trends in local and transported PM2.5 pollution in New York City

Abstract

Previous source apportionment analyses of New York City (NYC) PM2.5 have found that transported pollution can account for up to half of total fine particulate matter (PM2.5) mass. In recent years, several local and federal emissions regulations on both the transportation and energy sector have been introduced, such as the Clean Heavy-Duty Bus and Truck Rule, and policies related to the NYC Clean Heat Program. Since the implementation of these regulations, there have been limited studies on regional transport of particulate air pollution into NYC. This paper aims to quantify long-term changes in local and regional contributions to PM2.5 in NYC. The composition of PM2.5 in NYC over the period 2002–2018 was evaluated using data from the US Environmental Protection Agency (EPA) Chemical Speciation Network (CSN) and the New York City Community Air Survey (NYCCAS). Background site data obtained from EPA CSN was used to assess regional transport. Two estimates of transported PM2.5 were calculated, one assuming that transported PM2.5 consists solely of ammonium sulfate and ammonium nitrate as a lower bound and the other taking into account organic matter (OM) as an upper bound. Using this method, regional transport was estimated to account for 25–46% of total PM2.5 measured in NYC in 2018, down from 46 to 57% in 2002. Secondary PM2.5 output from the Community MultiScale Air Quality (CMAQ) model for the years 2008, 2011, and 2017 was used as an additional upper-bound estimate of regional transport (56%, 35%, and 30%, respectively). In addition to CMAQ model estimates of sulfate, nitrate, and primary emitted PM2.5, land-use regression (LUR) models for sulfur, vanadium, copper, nickel, and PM2.5 measurements at 60 locations across NYC during the winter and summer seasons of 2008–2015 were assessed for changes in local emissions. The results indicate decreased emissions from residual oil burning, traffic, and ships. As a consequence of regional and local changes, PM2.5 in NYC had fallen to approximately 55% of its 2002 levels by 2018. The observed temporal and spatial trends of PM2.5 and its components point to the effect of regulations as well as economic influences on fuel usage, such as the decline of coal in favor of natural gas, in reducing air pollution over the last two decades. While other major PM2.5 constituents have declined, OM is becoming an increasingly dominant component with potential implications for PM2.5 toxicity. Further improvements in NYC air quality could be achieved by targeting sources of ambient OM, such as commercial cooking, traffic, and biomass burning for residential heating.