This study utilizes multiple aerosol datasets collected in Metro Manila, Philippines to investigate sea salt aerosol characteristics. This coastal megacity allows for an examination of the impacts of ...precipitation and mixing of different air masses on sea salt properties, including overall concentration and size-resolved composition, hygroscopicity, and morphology. Intensive size-resolved measurements with a Micro-Orifice Uniform Deposit Impactor (MOUDI) between July–December 2018 revealed the following major results: (i) sea salt levels exhibit wide variability during the wet season, driven primarily by precipitation scavenging; (ii) ssNa+ and Cl− peaked in concentration between 1.8 and 5.6 μm, with Cl− depletion varying between 21.3 and 90.7%; (iii) mixing of marine and anthropogenic air masses yielded complex non-spherical shapes with species attached to the outer edges and Na+ uniformly distributed across particles unlike Cl−; (iv) there was significant contamination of sea salt aerosol by a variety of crustal and anthropogenic pollutants (Fe, Al, Ba, Mn, Pb, NO3−, V, Zn, NH4+); (v) categorization of samples in five different pollutant type categories (Background, Clean, Fire, Continental Pollution, Highest Rain) revealed significant differences in overall Cl− depletion with enhanced depletion in the submicrometer range versus the supermicrometer range; (vi) κ values ranged from 0.02 to 0.31 with a bimodal profile across all stages, with the highest value coincident with the highest sea salt volume fraction in the 3.2–5.6 μm stage, which is far lower than pure sea salt due to the significant influence of organics and black carbon. Analysis of longer term PM2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) and PMcoarse (= PM10 – PM2.5) data between August 2005 and October 2007 confirmed findings from the MOUDI data that more Cl− depletion occurred both in the wet season versus the dry season and on weekdays versus weekend days. This study demonstrates the importance of accounting for two factors in future studies on sea salt: (i) non-sea salt (nss) sources of Na+ impact calculations such as for Cl− depletion that typically assume that total Na+ concentration is derived from salt; and (ii) considering precipitation data over a larger spatial domain rather than a point measurement at the study site to investigate wet scavenging.
•Precipitation ranged widely and governed variability in sea salt concentrations.•Mixing of sea salt with other air masses manipulated sea salt properties.•Hygroscopicity (κ ~ 0.3) was highest where sea salt was most enhanced (3.2–5.6 μm).•Accounting for non-sea salt sources of Na+ impacts calculations relevant to sea salt.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study analyzes long-range transport of aerosol and aerosol chemical characteristics based on instances of high- and low-aerosol-loading events determined via ground-based size-resolved aerosol ...measurements collected at the Manila Observatory in Metro Manila, Philippines, from July to October 2018. Multiple data sources, including models, remote sensing, and in situ measurements, are used to analyze the impacts of long-range aerosol transport on Metro Manila and the conditions at the local and synoptic scales facilitating this transport. Through the use of case studies, evidence of long-range transport of biomass burning aerosol and continental emissions is identified in Metro Manila. Long-range transport of biomass burning aerosol from the Maritime Continent, bolstered by southwesterly flow and permitted by low rainfall, was identified through model results and the presence of biomass burning tracers (e.g., K, Rb) in the ground-based measurements. The impacts of emissions transported from continental East Asia on the aerosol characteristics in Metro Manila are also identified; for one of the events analyzed, this transport was facilitated by the nearby passage of a typhoon. Changes in the aerosol size distributions, water-soluble chemical composition, and contributions of various organic aerosol species to the total water-soluble organic aerosol were examined for the different cases. The events impacted by biomass burning transport had the overall highest concentration of water-soluble organic acids, while the events impacted by long-range transport from continental East Asia showed high percent contributions from shorter-chain dicarboxylic acids (i.e., oxalate) that are often representative of photochemical and aqueous processing in the atmosphere. The low-aerosol-loading event was subject to a larger precipitation accumulation than the high-aerosol events, indicative of wet scavenging as an aerosol sink in the study region. This low-aerosol event was characterized by a larger relative contribution from supermicrometer aerosols and had a higher percent contribution from longer-chain dicarboxylic acids (i.e., maleate) to the water-soluble organic aerosol fraction, indicating the importance of both primary aerosol emissions and local emissions.
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.
In this study, we describe the chemical and physical characteristics of two air pollution events in the first half of January 2020 in Metro Manila, Philippines, namely the New Year's eve fireworks ...and the Taal volcano ashfall. During the New Year's eve fireworks, PM2.5 concentration and most of the chemical components increased three-fold. However, we found disproportionately higher increases for certain metallic components typically used as pyrotechnic propellant and/or colorant for blue, white, and green light: Fe(5-fold), Cr(5-fold), Cu(8-fold), Ni(9-fold), V(10-fold), Ti(11-fold), and Ba(34-fold). These results provide insights for health assessments and legislation related to fireworks emissions. On January 12, 2020, the Taal volcano eruption caused much concern in Metro Manila as visible tephra deposits were observed. There was only a slight increase (8%) in PM2.5 concentration and its components related to basaltic ash. The low PM2.5 concentration was mainly due to the inhibited intrusion of ash into the stable nocturnal boundary layer. In addition, the detection of lightning in the plume and umbrella region showed size segregation of ash particles. The WRF-Chem model was able to capture the distribution of both tephra advection and fallout, a first for Taal volcano, making it possible for use in the future ashfall forecasting.
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•Two air pollution events on January 2020 in Metro Manila, Philippines were investigated.•High levels of toxic metallic elements were found during New Year's celebratory fireworks.•PM2.5 deposition from Taal volcano eruption was inhibited by the stable nocturnal boundary layer.•WRF-Chem successfully simulated the size and spatial distribution of the volcanic ash plume.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Size-resolved aerosol samples were collected in Metro Manila between July 2018 and October 2019. Two Micro-Orifice Uniform Deposit Impactors (MOUDI) were deployed at Manila Observatory in Quezon ...City, Metro Manila with samples collected on a weekly basis for water-soluble speciation and mass quantification. Additional sets were collected for gravimetric and black carbon analysis, including during special events such as holidays. The unique aspect of the presented data is a year-long record with weekly frequency of size-resolved aerosol composition in a highly populated megacity where there is a lack of measurements. The data are suitable for research to understand the sources, evolution, and fate of atmospheric aerosols, as well as studies focusing on phenomena such as aerosol-cloud-precipitation-meteorology interactions, regional climate, boundary layer processes, and health effects. The dataset can be used to initialize, validate, and/or improve models and remote sensing algorithms.
Fireworks degrade air quality, reduce visibility, alter atmospheric chemistry, and cause short-term adverse health effects. However, there have not been any comprehensive physicochemical and optical ...measurements of fireworks and their associated impacts in a Southeast Asia megacity, where fireworks are a regular part of the culture. Size-resolved particulate matter (PM) measurements were made before, during, and after New Year 2019 at the Manila Observatory in Quezon City, Philippines, as part of the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex). A high-spectral-resolution lidar (HSRL) recorded a substantial increase in backscattered signal associated with high aerosol loading ∼440 m above the surface during the peak of firework activities around 00:00 (local time). This was accompanied by PM2.5 concentrations peaking at 383.9 µg m−3. During the firework event, water-soluble ions and elements, which affect particle formation, growth, and fate, were mostly in the submicrometer diameter range. Total (>0.056 µm) water-soluble bulk particle mass concentrations were enriched by 5.7 times during the fireworks relative to the background (i.e., average of before and after the firework). The water-soluble mass fraction of PM2.5 increased by 18.5 % above that of background values. This corresponded to increased volume fractions of inorganics which increased bulk particle hygroscopicity, kappa (κ), from 0.11 (background) to 0.18 (fireworks). Potassium and non-sea-salt (nss) SO42- contributed the most (70.9 %) to the water-soluble mass, with their mass size distributions shifting from a smaller to a larger submicrometer mode during the firework event. On the other hand, mass size distributions for NO3-, Cl−, and Mg2+ (21.1 % mass contribution) shifted from a supermicrometer mode to a submicrometer mode. Being both uninfluenced by secondary aerosol formation and constituents of firework materials, a subset of species were identified as the best firework tracer species (Cu, Ba, Sr, K+, Al, and Pb). Although these species (excluding K+) only contributed 2.1 % of the total mass concentration of water-soluble ions and elements, they exhibited the highest enrichments (6.1 to 65.2) during the fireworks. Surface microscopy analysis confirmed the presence of potassium/chloride-rich cubic particles along with capsule-shaped particles in firework samples. The results of this study highlight how firework emissions change the physicochemical and optical properties of water-soluble particles (e.g., mass size distribution, composition, hygroscopicity, and aerosol backscatter), which subsequently alters the background aerosol's respirability, influence on surroundings, ability to uptake gases, and viability as cloud condensation nuclei (CCN).
A 16-month (July 2018–October 2019) dataset of size-resolved aerosol
composition is used to examine the sources and characteristics of five
organic acids (oxalate, succinate, adipate, maleate, ...phthalate) and
methanesulfonate (MSA) in Metro Manila, Philippines. As one of the most
polluted megacities globally, Metro Manila offers a view of how diverse
sources and meteorology impact the relative amounts and size distributions
of these species. A total of 66 sample sets were collected with a
Micro-Orifice Uniform Deposit Impactor (MOUDI), of which 54 sets were
analyzed for composition. Organic acids and MSA surprisingly were less
abundant than in other global regions that are also densely populated. The
combined species accounted for an average of 0.80 ± 0.66 % of total
gravimetric mass between 0.056 and 18 µm, still leaving 33.74 % of
mass unaccounted for after considering black carbon and water-soluble ions
and elements. The unresolved mass is suggested to consist of
non-water-soluble metals as well as both water-soluble and non-water-soluble
organics. Oxalate was approximately an order of magnitude more abundant than
the other five species (149 ± 94 ng m−3 versus others being
< 10 ng m−3) across the 0.056–18 µm size range. Both
positive matrix factorization (PMF) and correlation analysis are conducted
with tracer species to investigate the possible sources of organic acids
and MSA. Enhanced biomass burning influence in the 2018 southwest monsoon
resulted in especially high levels of submicrometer succinate, MSA, oxalate,
and phthalate. Peculiarly, MSA had negligible contributions from marine
sources but instead was linked to biomass burning and combustion. Enhanced
precipitation during the two monsoon seasons (8 June–4 October 2018 and
14 June–7 October 2019) coincided with a stronger influence from local
emissions rather than long-range transport, leading to notable concentration
enhancements in both the sub- and supermicrometer ranges for some species
(e.g., maleate and phthalate). While secondary formation via gas-to-particle
conversion is consistent with submicrometer peaks for the organic acids and
MSA, several species (i.e., phthalate, adipate, succinate, oxalate)
exhibited a prominent peak in the coarse mode, largely owing to their
association with crustal emissions (i.e., more alkaline aerosol type) rather
than sea salt. Oxalate's strong association with sulfate in the
submicrometer mode supports an aqueous-phase formation pathway for the study
region. However, high concentrations during periods of low rain and high
solar radiation suggest photo-oxidation is an important formation pathway.
Wet scavenging is the most important sink for particulate matter (PM) and is expected to decrease PM concentrations in the wet season. However, Metro Manila, Philippines has highly similar PM mass ...across seasons despite large differences in seasonal rainfall. It is important to identify factors contributing to seasonally consistent PM mass as these may be present in similar developing megacities besides Metro Manila, leading to PM accumulation and posing significant health risks. We use size-resolved aerosol composition, aerosol optical depth, and meteorological data to reveal that the seasonally consistent PM mass in Metro Manila is due to (1) opposing seasonal cycles of black carbon and water-soluble PM, (2) inefficient scavenging by short rain events (<1 h), and (3) the high frequency (50%) of these short rain events. Water-soluble PM was most sensitive to scavenging within the 0.18-1.0 μm and 1.8-5.6 μm size ranges but more clearly for rain events lasting over an hour, pointing to the importance of rain duration for efficient scavenging. We demonstrate that the presence of rain does not imply wet scavenging is taking place efficiently and rain characteristics are critical to properly estimating wet scavenging. In a changing climate, our understanding of factors such as rain duration and aerosol accumulation will become more important for guiding air quality-related policymaking and ensuring sustainable growth in developing megacities.
Seasonal particulate matter concentrations in Metro Manila, Philippines are consistent even with higher rain amounts in the wet season. Inefficient scavenging by rain events shorter than one hour is an important contributor to this seasonal feature.
Fine particulate matter (PM2.5) concentrations in Metro Manila, Philippines have consistently exceeded the guideline values set by the World Health Organization (WHO). Although there has been much ...progress in understanding the components and sources of PM2.5, limited research has been done on the influence of meteorological factors. In particular, the influence of the planetary boundary layer height (PBLH) on PM2.5 concentration has not been studied due to inadequate observations. From January 2019–June 2020, measurements from a High Spectral Resolution Lidar (HSRL) filled this gap and allowed for PBLH estimation and aerosol typing. This paper investigates the roles of PBLH and regional and local wind circulations on the temporal evolution of aerosol pollution. Results show that daytime and nighttime PBLH variability is associated with solar heating and radiative cooling, respectively. Cloud-free conditions during the dry season yield a higher PBL growth rate than during the wet season when lower daytime and elevated nighttime PBLH are observed. Lower PM2.5 levels are generally observed during daytime when PBLH is at its maximum. However, the PBLH has a significant inverse correlation with PM2.5 only in the months of December-January-February. We find that horizontal directional wind shear between synoptic and mesoscale circulations confounds the PM2.5 - PBLH relationship by creating stagnant conditions conducive to aerosol accumulation. The lower 20% of PM2.5 concentrations occur during the prevalence of strong monsoon winds. On the other hand, the upper 80% are found during the occurrence of compound mesoscale winds (i.e., sea/land/lake/valley/mountain breezes and channeling monsoon winds). In addition, mountain breeze is found to be associated with lifting of aerosols, resulting in multi-layering within the PBL. The findings in the present study emphasize the role of complex topography and mesoscale scale winds arising from the landscape on aerosol pollution variability.
•PM2.5 – PBLH - wind interactions were investigated in Metro Manila, Philippines.•Inverse correlation between PM2.5 and PBLH were observed only in the dry season.•Horizontal directional wind shear between mesoscale winds lead to PM2.5 accumulation.•Advection of marine airmass by strong southwest monsoon resulted in unvarying PBLH.•Mountain breeze lifts aerosols and creates multi-layering within the PBL.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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 burning
Ground‐based, size‐resolved measurements reveal that the ratio can be robust within the mixed layer for the submicrometer mode
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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