Search

Leveraging aerosol data from multiple airborne and surface‐based field campaigns encompassing diverse environmental conditions, we calculate statistics of the oxalate‐sulfate mass ratio (median: 0.0217; 95% confidence interval: 0.0154–0.0296; R = 0.76; N = 2,948). Ground‐based measurements of the oxalate‐sulfate ratio fall within our 95% confidence interval, suggesting the range is robust within the mixed layer for the submicrometer particle size range. We demonstrate that dust and biomass burning emissions can separately bias this ratio toward higher values by at least one order of magnitude. In the absence of these confounding factors, the 95% confidence interval of the ratio may be used to estimate the relative extent of aqueous processing by comparing inferred oxalate concentrations between air masses, with the assumption that sulfate primarily originates from aqueous processing. Plain Language Summary: The extent of atmospheric chemical processing remains an uncertain aspect of air mass characterization. Addressing this uncertainty is important because chemical reactions in the atmosphere in the presence of water (aqueous processing) produce a large fraction of global aerosol mass. The oxalate‐to‐sulfate ratio has been proposed as an indicator of aqueous processing, where higher values point to increased processing of an air mass. In this study, we quantify a range in the oxalate‐to‐sulfate mass ratio (0.0154–0.0296) using data from multiple field campaigns encompassing a diverse set of environments. This range is robust near the surface for particles below 1 micrometer in diameter. Larger particles, especially dust, and biomass burning particles significantly affect the oxalate‐to‐sulfate ratio and thus may confound the interpretation of a high oxalate‐to‐sulfate ratio as a signal of aqueous processing. In the absence of dust and biomass burning particles, the oxalate‐to‐sulfate ratio range may be used to compare the relative extent of aqueous processing between different air masses. Key Points: Oxalate‐sulfate mass ratios show similarity across multiple environments (95% confidence interval: 0.0154–0.0296; R = 0.76; N = 2,948)Oxalate‐sulfate mass ratio is biased toward higher values in presence of coarse aerosol particles and/or biomass burningGround‐based, size‐resolved measurements reveal that the ratio can be robust within the mixed layer for the submicrometer mode [ABSTRACT FROM AUTHOR]

We present the first study of the weekly cycles (WCs) of chemically speciated and size‐resolved particulate matter (PM) in Metro Manila, Philippines, a coastal megacity located within a highly complex meteorological environment that is subject to both anthropogenic and natural sources. To measure PM, Micro‐Orifice Uniform Deposit Impactors (MOUDIs) were deployed in Metro Manila from August 2018 to October 2019 and samples were analyzed for ionic and elemental species, including black carbon (BC). The WC in Metro Manila varied remarkably across seasons, linked to shifts in meteorology, transport, and aerosol source. Identified aerosol sources were traffic, local and regional burning, dust, sea salt, and secondary aerosol formation. Direct emissions induced a late workweek peak, while secondary aerosol formation led to a weekend peak in response to precursor buildup mainly from traffic. Seasonal analysis revealed that local burning from solid waste management and agricultural fires induced a strong WC peak while regional burning emissions from the Maritime Continent (MC) and possibly the Asian continent elevated seasonal baseline concentrations of the WC. BC showed a seasonally persistent WC, consistent in magnitude, weekly peak timing, and particle size. The dominant submicrometer WC and the contribution of BC across seasons have important ramifications on public health and policymaking, which are also discussed. As many of the observed WC patterns are undetectable when using only bulk PM, this study demonstrates that a seasonal, size‐resolved, and chemically speciated characterization is required to more fully understand the driving mechanisms governing WCs. Key Points: Significant variability was observed in the weekly cycle of particulate matter (particle size and composition) as a function of seasonSubmicrometer aerosol peak timing indicates that secondary formation increases in response to precursor buildup, inducing a weekend peakBlack carbon showed a seasonally persistent weekly cycle, consistent in magnitude, weekly peak timing, and particle size [ABSTRACT FROM AUTHOR]