Decadal Trends in the Temperature Dependence of Summertime Urban PM_2.5 in the Northeast United States

Abstract

Temperature has been identified as a key control over particulate matter of diameters smaller than 2.5 μm (PM 2.5 ); however, the mechanisms controlling this phenomenon in urban areas have not been definitively elucidated. With increasing urbanization and associated heat-island effects as well as a warming climate, understanding the role that temperature plays in modulating urban aerosol mass is critical. We explore the link between temperature and aerosol mass using observations from seven cities in the Northeast U.S., finding that summertime PM 2.5 exhibits a strong linear dependence on temperature going back at least two decades. Early in this record, the leading cause of the PM 2.5 mass increase with temperature was an increase in the ammonium sulfate aerosol mass. We suggest that this was due to increased electricity consumption to support air conditioning on warmer days and the associated SO 2 emissions from coal burning power plants. Later in the record and in the present day, the leading cause of the linear correlation of PM 2.5 mass with temperature is the increase in organic aerosol mass with temperature. Effective policy for curbing high PM 2.5 events in the future will depend on understanding the factors influencing this temperature-dependent enhancement in organic aerosols specifically, whether they are related to biogenic emissions, anthropogenic emissions, or chemical processes.

Increasing Contributions of Temperature-Dependent Oxygenated Organic Aerosol to Summertime Particulate Matter in New York City

“…While PM composition was dominated by organics, the inorganics, excluding chloride, showed greater heatwave enhancements in Queens compared to Manhattan, including when normalized by CO (Tables S8 and S9). This was especially pronounced for sulfate (and associated ammonium), which showed a strong temperature dependence across the entire measurement intensive (Figure S22) and in prior work …”

“…This was especially pronounced for sulfate (and associated ammonium), which showed a strong temperature dependence across the entire measurement intensive (Figure S22) and in prior work. 56 3.5. Implications for Air Quality in Metropolitan NYC and Downwind Areas.…”

Linking gas, particulate, and toxic endpoints to air emissions in the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) version 1.0

“…Deposition of nitrogen has shifted from primarily oxidized nitrogen (nitrate) to reduced nitrogen (ammonia) (Li et al, 2016). Fine particle mass is no longer dominated by summertime sulfate (Chan et al, 2018), and the temperature dependence of summertime urban Northeast U.S. PM2.5 is now being modulated by organic aerosol (Vannucci and Cohen, 2022). Particulate sulfur is also becoming increasingly recognized as organic (Riva et al, 2019;Moch et al, 2018).…”

Discerning the Concentration and Bi‐Directional Flux of Ammonia in an Urban Estuary Using the Relaxed Eddy Accumulation Method

“…Wet deposition of NH 4 + is predicted to now constitute between 37% and 83% of wet inorganic N deposition in the USA (Davidson et al., 2011; Fenn et al., 2018). Moreover, reductions in NO x , as well as sulfur dioxide (SO 2 ), have decreased the amount of partitioning to the particle phase (i.e., p‐NH 4 + ), and thus increased the amount remaining in the gas phase (NH 3(g) ) (Requia et al., 2019; Van Damme et al., 2020; Vannucci & Cohen, 2022). Given the short depositional lifetime of NH 3(g) (0.5 hr–0.46 days, as opposed to 3.2 days for p‐NH 4 + ; Xu & Penner, 2012), the shift toward the gaseous phase has important implications for depositional patterns.…”