Abstract
Abstract. This paper presents novel results from size-resolved particulate matter (PM) mass, composition, and morphology measurements conducted during the 2018 southwest monsoon (SWM) season in Metro Manila, Philippines. Micro-orifice uniform deposit impactors (MOUDIs) were used to collect PM sample sets composed of size-resolved measurements at the following aerodynamic cut-point diameters (Dp): 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, 0.18, 0.10, and 0.056 µm. Each sample set was analyzed for composition of the water-soluble fraction. Analysis for mass was carried out on two sample sets, whereas black carbon (BC) and morphology analysis were analyzed on a single sample set. The bulk of the PM mass was between 0.18 and 1.0 µm with a dominant mode between 0.32 and 0.56 µm. Similarly, most of the black carbon (BC) mass was found between 0.10 and 1.0 µm, peaking between 0.18 and 0.32 µm. These peaks are located in the Greenfield gap, or the size range between 0.10 and 1.0 µm, where wet scavenging by rain is relatively inefficient. In the range between 0.10 and 0.18 µm, BC constituted 78.1 % of the measured mass. Comparable contributions of BC (26.9 %) and the water-soluble fraction (33.4 %) to total PM were observed and most of the unresolved mass, which amounted to 39.6 % in total, was for diameters exceeding 0.32 µm. The water-soluble ions and elements exhibited an average combined concentration of 8.53 µg m−3, with SO42-, NH4+, NO3-, Na+, and Cl− as the major contributors. Positive matrix factorization (PMF) was applied to identify the possible aerosol sources and estimate their contribution to the water-soluble fraction of collected PM. The factor with the highest contribution was attributed to “aged aerosol” (48.0 %), while “sea salt” (22.5 %) and “combustion” emissions (18.7 %) had comparable contributions. “Vehicular/resuspended dust” (5.6 %) and “waste processing” emissions (5.1 %) were also identified. Microscopy analysis highlighted the ubiquity of nonspherical particles regardless of size, which is significant when considering calculations of parameters such as single scattering albedo, the asymmetry parameter, and the extinction efficiency. The significant influence from aged aerosol to Metro Manila during the SWM season indicates that local sources in this megacity do not fully govern this coastal area's aerosol properties. The fact that the majority of the regional aerosol mass burden is accounted for by BC and other insoluble components has important downstream effects on the aerosol hygroscopic properties, which depend on composition. The results are relevant for understanding the impacts of monsoonal features on size-resolved aerosol properties, notably aqueous processing and wet scavenging. Finally, the results of this work provide contextual data for future sampling campaigns in Southeast Asia such as the airborne component of the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) planned for the SWM season in 2019.
Highlights
Ambient atmospheric aerosol particles impact human health, visibility, climate, and the hydrological cycle
black carbon (BC) concentrations were quantified from set MO13 only, the results showed that BC was significantly correlated (r: 0.61–0.92) with 15 species, including those mentioned above and a few elements that were found via Positive matrix factorization (PMF) to be stronger contributors to the combustion source discussed in Sect. 3.3.3 (Ni, Cu, As, Se, Cd, Tl, and Pb)
– The total mass concentrations were measured on two occasions and were 18.3 and 49.6 μg m−3
Summary
Ambient atmospheric aerosol particles impact human health, visibility, climate, and the hydrological cycle. Major factors governing these behaviors, such as the deposition fraction in the respiratory system and activation into cloud condensation nuclei (CCN), include size and chemical composition. One region of interest for the characterization of PM is Southeast Asia due to increasing urbanization and the exposure of the population to a variety of aerosol sources, both natural and anthropogenic (Hopke et al, 2008). As of 2015, Metro Manila had a population of approximately 12.88 million (Philippine Statistics Authority, 2015). Of the cities comprising the Metro Manila area, the one that is the focus of this study, Quezon City, is the most populated (2.94 million people) with a population density of ∼ 17 000 km−2 as of 2015 (Philippine Statistics Authority, 2015)
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