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High-spatial-resolution mapping and source apportionment of aerosol composition in Oakland, California, using mobile aerosol mass spectrometry

Atmospheric chemistry and physics, 2018-11, Vol.18 (22), p.16325-16344 [Peer Reviewed Journal]

COPYRIGHT 2018 Copernicus GmbH ;2018. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License. ;ISSN: 1680-7324 ;ISSN: 1680-7316 ;EISSN: 1680-7324 ;DOI: 10.5194/acp-18-16325-2018

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  • Title:
    High-spatial-resolution mapping and source apportionment of aerosol composition in Oakland, California, using mobile aerosol mass spectrometry
  • Author: Shah, Rishabh U. ; Robinson, Ellis S. ; Gu, Peishi ; Robinson, Allen L. ; Apte, Joshua S. ; Presto, Albert A.
  • Subjects: Aerosol composition ; Aerosols ; Air masses ; Air sampling ; Black carbon ; Canyons ; Central business districts ; Chemical properties ; Cooking ; Environmental aspects ; Freight transportation ; Gases ; Gasoline ; Gasoline engines ; Hydroxyl radicals ; Mass spectrometry ; Mass spectroscopy ; Mathematical analysis ; Matrix methods ; Methods ; Organic chemistry ; Particulate emissions ; Particulate matter ; Particulates ; Photochemicals ; Photochemistry ; Ratios ; Residential areas ; Restaurants ; Shipping ; Spatial discrimination ; Spatial variations ; Street canyons ; Sulfates ; Suspended particulate matter ; Traffic ; Trucks ; Urban areas ; Vehicle emissions ; Ventilation
  • Is Part Of: Atmospheric chemistry and physics, 2018-11, Vol.18 (22), p.16325-16344
  • Description: We investigated spatial and temporal patterns in the concentration and composition of submicron particulate matter (PM1) in Oakland, California, in the summer of 2017 using an aerosol mass spectrometer mounted in a mobile laboratory. We performed ∼160 h of mobile sampling in the city over a 20-day period. Measurements are compared for three adjacent neighborhoods with distinct land uses: a central business district (“downtown”), a residential district (“West Oakland”), and a major shipping port (“port”). The average organic aerosol (OA) concentration is 5.3 µg m−3 and contributes ∼50 % of the PM1 mass. OA concentrations in downtown are, on average, 1.5 µg m−3 higher than in West Oakland and port. We decomposed OA into three factors using positive matrix factorization: hydrocarbon-like OA (HOA; 20 % average contribution), cooking OA (COA; 25 %), and less-oxidized oxygenated OA (LO-OOA; 55 %). The collective 45 % contribution from primary OA (HOA + COA) emphasizes the importance of primary emissions in Oakland. The dominant source of primary OA shifts from HOA-rich in the morning to COA-rich after lunchtime. COA in downtown is consistently higher than West Oakland and port due to a large number of restaurants. HOA exhibits variability in space and time. The morning-time HOA concentration in downtown is twice that in port, but port HOA increases more than two-fold during midday, likely because trucking activity at the port peaks at that time. While it is challenging to mathematically apportion traffic-emitted OA between drayage trucks and cars, combining measurements of OA with black carbon and CO suggests that while trucks have an important effect on OA and BC at the port, gasoline-engine cars are the dominant source of traffic emissions in the rest of Oakland. Despite the expectation of being spatially uniform, LO-OOA also exhibits spatial differences. Morning-time LO-OOA in downtown is roughly 25 % (∼0.6 µg m−3) higher than the rest of Oakland. Even as the entire domain approaches a more uniform photochemical state in the afternoon, downtown LO-OOA remains statistically higher than West Oakland and port, suggesting that downtown is a microenvironment with higher photochemical activity. Higher concentrations of particulate sulfate (also of secondary origin) with no direct sources in Oakland further reflect higher photochemical activity in downtown. A combination of several factors (poor ventilation of air masses in street canyons, higher concentrations of precursor gases, higher concentrations of the hydroxyl radical) likely results in the proposed high photochemical activity in downtown. Lastly, through Van Krevelen analysis of the elemental ratios (H ∕ C, O ∕ C) of the OA, we show that OA in Oakland is more chemically reduced than several other urban areas. This underscores the importance of primary emissions in Oakland. We also show that mixing of oceanic air masses with these primary emissions in Oakland is an important processing mechanism that governs the overall OA composition in Oakland.
  • Publisher: Katlenburg-Lindau: Copernicus GmbH
  • Language: English
  • Identifier: ISSN: 1680-7324
    ISSN: 1680-7316
    EISSN: 1680-7324
    DOI: 10.5194/acp-18-16325-2018
  • Source: DOAJ Directory of Open Access Journals
    GFMER Free Medical Journals
    Alma/SFX Local Collection
    ProQuest Central
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