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

Abstract

As part of the summer 2022 NYC-METS (New York City metropolitan Measurements of Emissions and TransformationS) campaign and the ASCENT (Atmospheric Science and Chemistry mEasurement NeTwork) observational network, speciated particulate matter was measured in real time in Manhattan and Queens, NY, with additional gas-phase measurements. Largely due to observed reductions in inorganic sulfate aerosol components over the 21st century, summertime aerosol composition in NYC has become predominantly organic (80−83%). Organic aerosol source apportionment via positive matrix factorization showed that this is dominated by secondary production as oxygenated organic aerosol (OOA) source factors comprised 73−76% of OA. Primary factors, including cooking-related organic aerosol (COA) and hydrocarbon-like organic aerosol (HOA) comprised minor fractions of OA, only 13−15% and 10−11%, respectively. The two sites presented considerable spatiotemporal variations in OA source factor concentrations despite similar average PM 2.5 concentrations. The less-and more-oxidized OOA factors exhibited clear temperature dependences at both sites with increased concentrations and greater degrees of oxidation at higher temperatures, including during a heatwave. With strong temperature sensitivity and minimal changes in summertime concentrations since 2001, secondary OA poses a particular challenge for air quality policy in NYC that will very likely be exacerbated by continued climate change and extreme heat events.

Aged and obscured wildfire smoke associated with downwind health risks

“…COA is determined by prominent signals at m/z 41 and 55 with a higher f55-to-f57 ratio than that of HOA with elevated concentration at around lunch and dinner times. Other than BBOA and aBBOA, the types of organic aerosol factors apportioned in this study are consistent with a previous study performed at the same location during the previous summer (without major wildfire activity) (Hass-Mitchell et al, 2024).…”

“…License: CC BY-NC-ND 4.0 enabled by long-term, continuous, and accurate monitoring of the speciated PM2.5 measured here (e.g., ASCENT network) in major populated areas to enable future epidemiological studies across different populations and health outcomes. The ensuing scientific evidence on which sources and chemical/physical particle characteristics (e.g., age, oxidation) are most harmful could aid effective decision-making to protect public health, especially as PM2.5 reductions have largely stagnated at levels with continued health risks (Hass-Mitchell et al, 2024;Weichenthal et al, 2022). In addition to real-time PM speciation like that leveraged here, characteristics such as potential oxidative stress are not routinely measured in large-scale regulatory networks, further demonstrating the need for additional monitoring and subsequent health analysis.…”

“…The May 15 to June 13, 2023 study period included the major Quebec wildfire smoke transport episode (i.e., June 6-9), as well as several other smoke transport events spanning Western to Eastern Canada. Yet, equally important, this study period allowed us to focus on smoke-related contributions to less-and more-oxidized organic aerosol components prior to the onset of hotter summertime temperatures with more secondary organic aerosol contributions from other temperature-dependent sources and processes, as shown in prior work at the site (Hass-Mitchell et al, 2024). By using this study period, we were able to better isolate the contributions of oxidized transported smoke to the generic oxidized organic aerosol factors across the 5 different smoke events with reduced temperature-related influences compared to during the summer.…”

“…Simultaneously, due to climate change, wildfires have emerged as increasingly important sources of PM2.5 as well as other air pollutants and reactive compounds (Burke et al, 2023;Bourgeois et al, 2021). The composition of wildfire and other biomass burning smoke has been increasingly investigated, including laboratory combustion experiments (Koss et al, 2018;Hatch et al, 2015), oxidation chamber studies (Coggon et al, 2019;Lim et al, 2019;Joo et al, 2019;Joo et al, 2024), and aircraft-based measurements of https://doi.org/10.26434/chemrxiv-2024-6zb16 ORCID: https://orcid.org/0000-0002-8252-4232 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 a comparison of the smoke events studied here demonstrates that the smoke episodes which were more dilute during transit (i.e., 1 st -3 rd events) had a greater extent of oxidation despite having a similar range of transport times as the less oxidized 5 th event (Figs.…”

High-Resolution Modeling of Summertime Biogenic Isoprene Emissions in New York City

“…The increased BVOCs can lead to formation of secondary particulate matter. Summertime aerosol composition in NYC is now primarily organic; these oxygenated organic aerosols are formed from an uncertain mix of both biogenic and anthropogenic VOCs, and their emissions show significant temperature dependence . Future increased BVOC and decreased AVOC emissions will likely enhance the biogenic organic aerosol load and its temperature-dependent formation rate.…”