Lead sources detected in Manila's air after the phase-out of leaded gasoline

Atmospheric Environment · 2025-12-02

Airborne cloud water pH measurements in diverse regions: statistics and relationships with constituents

Environmental Science Atmospheres · 2025-01-01 · 2 citations

This study uses airborne cloud water data to investigate acidity in three regions, which has implications for atmospheric chemistry and effects on human health and ecosystems.

Influence of wildfire smoke on summertime surface air quality in an urban desert region

Atmospheric Environment · 2025-05-16 · 4 citations

Day-Night Shifts in Water-Soluble Ions of Size-Resolved Aerosols before and after the COVID-19 Lockdown in a Coastal Megacity: Metro Manila, Philippines

ACS Earth and Space Chemistry · 2025-10-09

The COVID-19 pandemic-driven lockdowns offer a unique opportunity to examine how reductions in anthropogenic emissions impacted atmospheric aerosol composition in urban environments. This study investigates the day-night variability of size-resolved water-soluble ions in ambient particulate matter (PM) collected in Metro Manila before (November 2019–February 2020) and after (November 2020–February 2021) lockdown implementation. Using tandem Micro-Orifice Uniform Deposit Impactors (MOUDIs), aerosol samples were collected during daytime (06:00–18:00) and nighttime (18:00–06:00) periods and analyzed for key ionic species (sulfate, ammonium, nitrate, oxalate, sodium, chloride, calcium, and magnesium) via ion chromatography. Submicrometer water-soluble mass declined post-lockdown, particularly during daytime, reflecting suppressed secondary formation under reduced anthropogenic activity, with substantial reductions in sulfate and ammonium. In contrast, concentrations in the supermicrometer range increased due to naturally higher sea salt levels. Chemical ratios reveal notable features post-lockdown and during daytime due to especially reduced sulfate levels: reduced chloride depletion (on percent basis), higher ammonium-to-sulfate ratios pointing to more excess ammonia available for reactions beyond neutralizing sulfate, and support for aqueous-phase processing preferentially forming more oxalate relative to sulfate. These findings underscore how both photochemistry and changes in anthropogenic activity influence aerosol composition, with implications for air quality and atmospheric processing in coastal urban cities.

Ozone in the Desert Southwest of the United States: A Synthesis of Past Work and Steps Ahead

ACS ES&T Air · 2024-01-24 · 18 citations

A region often neglected in the grander scale of general atmospheric chemistry studies and model evaluation for gas-phase chemistry is the desert southwest of the U.S. Despite regulatory progress, challenges in meeting the National Ambient Air Quality Standard for ozone motivate a re-examination of the unique meteorological conditions, interactions between the desert, agricultural, and built environmental landscapes, emissions across natural and anthropogenic sources, and regional transport of precursors that govern ozone formation in the desert Southwest. Arizona includes multiple nonattainment counties with a unique situation in terms of its environment (e.g., vegetation, meteorology, fire prone areas), complex terrain, urban growth, transport vulnerability, and limited knowledge base. Here we summarize past works investigating the ozone over Arizona, including 61 peer-reviewed publications found since the first one in 1996, and determine significant knowledge gaps to guide future research with the aim of improving regulatory policy. A more in-depth focus is placed here on Maricopa County, which includes the Phoenix Metropolitan area, where significant population growth in recent decades coupled with the extreme high temperatures and surrounding complex terrain creates a poorly understood airshed in terms of ozone chemistry, thereby complicating regulatory decisions. We suggest paths forward, including improved monitoring, assessment, and modeling tools for the region, better leveraging of archived data, and engagement with the public, government, and policy. This Review is highly relevant as well to other semiarid and arid regions, which represent the most common land type globally, warranting more attention.

Comment on egusphere-2022-166

2022-06-16

Cloud droplet composition is a key observable quantity that can aid understanding of how aerosols and clouds interact. As part of the Clouds, Aerosols and Monsoon Processes – Philippines Experiment (CAMP2Ex), three case studies were analyzed involving collocated airborne sampling of relevant clear and cloudy airmasses associated with maritime warm convection. Two of the cases represented a polluted marine background, with signatures of transported East Asian regional pollution, aged over water for several days, while the third case comprised a major smoke transport event from Kalimantan fires. Sea salt was a dominant component of cloud droplet composition, in spite of fine particulate enhancement from regional anthropogenic sources. Furthermore, the proportion of sea salt was enhanced relative to sulfate in rainwater and may indicate both a propensity for sea salt to aid warm rain production and an increased collection efficiency of large sea salt particles by rain in subsaturated environments. Amongst cases, as precipitation became more significant, so too did the variability in the sea salt to (non-sea salt) sulfate ratio. Across cases, nitrate and ammonium were fractionally greater in cloud water than fine-mode aerosol particles; however, a strong co-variability in cloud water nitrate and sea salt was suggestive of prior uptake of nitrate on large salt particles. A mass-based closure analysis of non-sea salt sulfate compared the cloud water air-equivalent mass concentration to the concentration of aerosol particles serving as cloud condensation nuclei for droplet activation. While sulfate found in cloud was generally constrained by the sub-cloud aerosol concentration, there was significant intra-cloud variability that was attributed to entrainment – causing evaporation of sulfate containing droplets – and losses due to precipitation. In addition, precipitation tended to promote mesoscale variability in the sub-cloud aerosol through a combination of removal, convective downdrafts, and through dynamically-driven convergence. Physical mechanisms exerted such strong control over the cloud water compositional budget that it was not possible to isolate any signature of chemical production/loss using in-cloud observations. The cloud-free environment surrounding the non-precipitating, smoke case indicated sulfate enhancement compared to convective mixing quantified by a stable gas tracer; however, this was not observed in the cloud water (either through use of ratios or the mass closure) perhaps implying that the warm convective cloud time scale was too short for chemical production to be a leading-order budgetary term. Closure of other species was truncated by incomplete characterization of coarse aerosol (e.g., it was found that only 10-50% of sea salt mass found in cloud was captured during clear air sampling) and unmeasured gas phase abundances affecting closure of semi-volatile aerosol species (e.g., ammonium, nitrate and organic aerosols) and soluble volatile organic compound contributions to total organic carbon in cloud water.

Extreme Heat Impacts on the Viability of Alternative Transportation for Reducing Ozone Pollution: A Case Study from Maricopa County, Arizona

Weather Climate and Society · 2022-06-03 · 8 citations

Abstract One commonly proposed strategy for reducing urban air pollution is transitioning from single-occupancy vehicle (SOV) travel to alternative transportation (AT) modes, such as walking, biking, and using public transportation. While many studies have addressed the benefits of switching from SOV to AT, fewer studies have examined the potential for negative outcomes due to increased exposure to heat when using AT modes. This work uses Maricopa County, Arizona, home to the metropolitan Phoenix area, as a test case to examine the potential impacts of heat on commuters who utilize AT. First, regions of the county with the most candidates for switching from SOV to AT were identified and used to develop an AT candidate index. This index was based on both the current rates of AT use and the number of SOV commuters with the shortest commuting times in the dataset (<10 min). Next, typical weather conditions during warnings for high ozone (O 3 ) pollution were examined. From 2017 to 2020, over one-quarter of all days with an O 3 warning also were subject to an excessive heat warning. Last, land surface temperature data were used to determine the potential for increased heat exposure during AT commuting at both the ZIP code and AT infrastructure (public transit stops and bikeways) scales. Although this work focuses on Maricopa County, the issues presented here are increasingly relevant for cities across the world that are subject to poor air quality, hotter temperatures, and heat waves.

Impact of environmental factors on heat-associated mortalities in an urban desert region

International Journal of Biometeorology · 2022-09-10 · 7 citations

Abstract The troubling trend of rising heat-associated mortalities in an urban desert region (Maricopa County, AZ, USA) has motivated us to explore the extent to which environmental factors may contribute to increased heat-health risks. Summertime data from 2010 to 2019 were used to construct a suite of models for daily heat-associated mortalities. The best-performing full model included the following predictors, ordered from strongest to weakest influence: daily average air temperature, average of previous 5 days daily average air temperature, year, day of year, average of previous 5 days daily average dew point temperature, average of previous 5 days daily average PM 2.5 , and daily average PM 10 . This full model exhibited a 5.39% reduction in mean absolute error in daily heat-associated mortalities as compared to the best-performing model that included only air temperature as an environmental predictor. The extent to which issued and modeled excessive heat warnings (from both the temperature only and full models) corresponded with heat-associated mortalities was also examined. Model hindcasts for 2020 and 2021 showed that the models were able to capture the high number of heat-associated mortalities in 2020, but greatly undercounted the highest yet observed number of heat-associated mortalities in 2021. Results from this study lend insights into environmental factors corresponding to an increased number of heat-associated mortalities and can be used for informing strategies towards reducing heat-health risks. However, as the best-performing model was unable to fully capture the observed number of heat-associated mortalities, continued scrutiny of both environmental and non-environmental factors affecting these observations is needed.

Measurement report: Closure analysis of aerosol–cloud composition in tropical maritime warm convection

Atmospheric chemistry and physics · 2022-10-17 · 25 citations

Abstract. Cloud droplet chemical composition is a key observable property that can aid understanding of how aerosols and clouds interact. As part of the Clouds, Aerosols and Monsoon Processes – Philippines Experiment (CAMP2Ex), three case studies were analyzed involving collocated airborne sampling of relevant clear and cloudy air masses associated with maritime warm convection. Two of the cases represented a polluted marine background, with signatures of transported East Asian regional pollution, aged over water for several days, while the third case comprised a major smoke transport event from Kalimantan fires. Sea salt was a dominant component of cloud droplet composition, in spite of fine particulate enhancement from regional anthropogenic sources. Furthermore, the proportion of sea salt was enhanced relative to sulfate in rainwater and may indicate both a propensity for sea salt to aid warm rain production and an increased collection efficiency of large sea salt particles by rain in subsaturated environments. Amongst cases, as precipitation became more significant, so too did the variability in the sea salt to (non-sea salt) sulfate ratio. Across cases, nitrate and ammonium were fractionally greater in cloud water than fine-mode aerosol particles; however, a strong covariability in cloud water nitrate and sea salt was suggestive of prior uptake of nitrate on large salt particles. A mass-based closure analysis of non-sea salt sulfate compared the cloud water air-equivalent mass concentration to the concentration of aerosol particles serving as cloud condensation nuclei for droplet activation. While sulfate found in cloud was generally constrained by the sub-cloud aerosol concentration, there was significant intra-cloud variability that was attributed to entrainment – causing evaporation of sulfate-containing droplets – and losses due to precipitation. In addition, precipitation tended to promote mesoscale variability in the sub-cloud aerosol through a combination of removal, convective downdrafts, and dynamically driven convergence. Physical mechanisms exerted such strong control over the cloud water compositional budget that it was not possible to isolate any signature of chemical production/loss using in-cloud observations. The cloud-free environment surrounding the non-precipitating smoke case indicated sulfate enhancement compared to convective mixing quantified by a stable gas tracer; however, this was not observed in the cloud water (either through use of ratios or the mass closure), perhaps implying that the warm convective cloud timescale was too short for chemical production to be a leading-order budgetary term and because precursors had already been predominantly exhausted. Closure of other species was truncated by incomplete characterization of coarse aerosol (e.g., it was found that only 10 %–50 % of sea salt mass found in cloud was captured during clear-air sampling) and unmeasured gas-phase abundances affecting closure of semi-volatile aerosol species (e.g., ammonium, nitrate and organic) and soluble volatile organic compound contributions to total organic carbon in cloud water.

Author response for "Stubborn aerosol: why particulate mass concentrations do not drop during the wet season in Metro Manila, Philippines"

2022-08-19