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.
Coastal southeast Florida experiences a wide range of aerosol conditions, including African dust, biomass burning (BB) aerosols, as well as sea salt and other locally-emitted aerosols. These aerosols ...are important sources of cloud condensation nuclei (CCN), which play an essential role in governing cloud radiative properties. As marine environments dominate the surface of Earth, CCN characteristics in coastal southeast Florida have broad implications for other regions with the added feature that this site is perturbed by both natural and anthropogenic emissions. This study investigates the influence of different air mass types on CCN concentrations at 0.2% (CCN0.2%) and 1.0% (CCN1.0%) supersaturation (SS) based on ground site measurements during selected months in 2013, 2017, and 2018. Average CCN0.2% and CCN1.0% concentrations were 373 ± 200 cm−3 and 584 ± 323 cm−3, respectively, for four selected days with minimal presence of African dust and BB (i.e., background days). CCN concentrations were not elevated on the four days with highest influence of African dust (289 ± 104 cm−3 0.2% SS and 591 ± 302 cm−3 1.0% SS), consistent with high dust mass concentrations comprised of coarse particles that are few in number. In contrast, CCN concentrations were substantially enhanced on the five days with the greatest impact from BB (1408 ± 976 cm−3 0.2% SS and 3337 ± 1252 cm−3 1.0% SS). Ratios of CCN0.2%:CCN1.0% were used to compare the hygroscopicity of the aerosols associated with African dust, BB, and background days. Average ratios were similar for days impacted by African dust and BB (0.54 ± 0.17 and 0.55 ± 0.17, respectively). A 29% higher average ratio was observed on background days (0.71 ± 0.14), owing in part to a strong presence of sea salt and reduced presence of more hydrophobic species such as those of a carbonaceous or mineral-dust nature. Finally, periods of heavy rainfall were shown to effectively decrease both CCN0.2% and CCN1.0% concentrations. However, the rate varied at which such concentrations increased after the rain. This work contributes knowledge on the nucleating ability of African dust and BB in a marine environment after varying periods of atmospheric transport (days to weeks). The results can be used to understand the hygroscopicity of these air mass types, predict how they may influence cloud properties, and provide a valuable model constraint when predicting CCN concentrations in comparable situations.
•African dust plumes do not perturb CCN concentrations in southeast Florida.•CCN concentrations are greatly increased on days influenced by biomass burning.•Heavy rainfall reduces CCN concentrations.•The duration varies for CCN concentrations to restore after periods of heavy rain.
The MONterey Aerosol Research Campaign (MONARC) in May–June 2019 featured 14 repeated identical flights off the California coast over the open ocean at the same time each flight day. The objective of ...this study is to use MONARC data along with machine learning analysis to evaluate relationships between both supermicrometer sea salt aerosol number (N>1) and volume (V>1) concentrations and wind speed, wind direction, sea surface temperature (SST), ambient temperature (Tamb), turbulent kinetic energy (TKE), relative humidity (RH), marine boundary layer (MBL) depth, and drizzle rate. Selected findings from this study include the following: (i) Near surface (<60 m) N>1 and V>1 concentration ranges were 0.1–4.6 cm−3 and 0.3–28.2 μm3 cm−3, respectively; (ii) four meteorological regimes were identified during MONARC with each resulting in different N>1 and V>1 concentrations and also varying horizontal and vertical profiles; (iii) the relative predictive strength of the MBL properties varies depending on predicting N>1 or V>1, with MBL depth being more highly ranked for predicting N>1 and with TKE being higher for predicting V>1; (iv) MBL depths >400 m (<200 m) often correspond to lower (higher) N>1 and V>1 concentrations; (v) enhanced drizzle rates coincide with reduced N>1 and V>1 concentrations; (vi) N>1 and V>1 concentrations exhibit an overall negative relationship with SST and RH and an overall positive relationship with Tamb; and (vii) wind speed and direction were relatively weak predictors of N>1 and V>1.
Key Points
Vertical and horizontal profiles of supermicron sea salt aerosol concentrations are related to synoptic conditions and air mass history
Marine boundary layer depth (turbulent kinetic energy) is the best predictor for supermicron sea salt aerosol number (volume) concentration
Drizzle rate is the second most influential parameter for both supermicron sea salt aerosol number and volume concentration
This study focuses on the long-term aerosol and precipitation chemistry measurements from colocated monitoring sites in Southern Florida between 2013 and 2018. A positive matrix factorization (PMF) ...model identified six potential emission sources impacting the study area. The PMF model solution yielded the following source concentration profiles: (i) combustion; (ii) fresh sea salt; (iii) aged sea salt; (iv) secondary sulfate; (v) shipping emissions; and (vi) dust. Based on these results, concentration-weighted trajectory maps were developed to identify sources contributing to the PMF factors. Monthly mean precipitation pH values ranged from 4.98 to 5.58, being positively related to crustal species and negatively related to SO42−. Sea salt dominated wet deposition volume-weighted concentrations year-round without much variability in its mass fraction in contrast to stronger seasonal changes in PM2.5 composition where fresh sea salt was far less influential. The highest mean annual deposition fluxes were attributed to Cl−, NO3−, SO42−, and Na+ between April and October. Nitrate is strongly correlated with dust constituents (unlike sea salt) in precipitation samples, indicative of efficient partitioning to dust. Interrelationships between precipitation chemistry and aerosol species based on long-term surface data provide insight into aerosol–cloud–precipitation interactions.
Chloride (Cl−) displacement from sea salt particles is an extensively studied phenomenon with implications for human health, visibility, and the global radiation budget. Past works have investigated ...Cl− depletion over the northwest Atlantic (NWA); however, an updated, multi-seasonal, and geographically expanded account of sea salt reactivity over the region is needed. This study uses chemically resolved mass concentrations and meteorological data from the airborne Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) to quantify seasonal, spatial, and meteorological trends in Cl− depletion and to explore the importance of quantifying (1) non-sea salt sources of Na+ and (2) mass concentrations of lost Cl− (instead of relative amounts displaced). Lost Cl− mass concentrations are lowest in December–February and March, moderate around Bermuda in June, and highest in May (median losses of 0.04, 0.04, 0.66, and 1.76 µg m−3, respectively), with losses in May that are high enough to potentially accelerate tropospheric oxidation rates. Inorganic acidic species can account for all Cl− depletion in December–February, March, and June near Bermuda but none of the lost Cl− in May, suggesting that organic acids may be of importance for Cl− displacement in certain months. Contributions of dust to Na+ are not important seasonally but may cause relevant overestimates of lost Cl− in smoke and dust plumes. Higher percentages of Cl− depletion often do not correspond to larger mass concentrations of lost Cl−, so it is highly recommended to quantify the latter to place depletion reactions in context with their role in atmospheric oxidation and radiative forcing.
A significant concern for public health and visibility is airborne particulate matter, especially during extreme events. Of most relevance for health, air quality, and climate is the role of fine ...aerosol particles, specifically particulate matter with aerodynamic diameters less than or equal to 2.5 micrometers (PM2.5). The purpose of this study was to examine PM2.5 extreme events between 1989 and 2018 at Mesa Verde, Colorado using Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring data. Extreme events were identified as those with PM2.5 on a given day exceeding the 90th percentile value for that given month. We examine the weekly, monthly, and interannual trends in the number of extreme events at Mesa Verde, in addition to identifying the sources of the extreme events with the aid of the Navy Aerosol Analysis and Prediction (NAAPS) aerosol model. Four sources were used in the classification scheme: Asian dust, non-Asian dust, smoke, and “other”. Our results show that extreme PM2.5 events in the spring are driven mostly by the dust categories, whereas summertime events are influenced largely by smoke. The colder winter months have more influence from “other” sources that are thought to be largely anthropogenic in nature. No weekly cycle was observed for the number of events due to each source; however, interannual analysis shows that the relative amount of dust and smoke events compared to “other” events have increased in the last decade, especially smoke since 2008. The results of this work indicate that, to minimize and mitigate the effects of extreme PM2.5 events in the southwestern Colorado area, it is important to focus mainly on smoke and dust forecasting in the spring and summer months. Wintertime extreme events may be easier to regulate as they derive more from anthropogenic pollutants accumulating in shallow boundary layers in stagnant conditions.
Monitoring and modeling aerosol particle life cycle in Southeast Asia (SEA) is challenged by high cloud cover, complex meteorology, and the wide range of aerosol species, sources, and transformations ...found throughout the region. Satellite observations are limited, and there are few in situ observations of aerosol extinction profiles, aerosol properties, and environmental conditions. Therefore, accurate aerosol model outputs are crucial for the region. This work evaluates the Navy Aerosol Analysis and Prediction System Reanalysis (NAAPS-RA) aerosol optical thickness (AOT) and light extinction products using airborne aerosol and meteorological measurements from the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) conducted in 2019 during the SEA southwest monsoon biomass burning season. Modeled AOTs and extinction coefficients are compared to those retrieved with a high spectral resolution lidar (HSRL-2). Agreement between simulated and retrieved AOT (R2= 0.78, relative bias =-5 %, normalized root mean square error (NRMSE) = 48 %) and aerosol extinction coefficients (R2= 0.80, 0.81, and 0.42; relative bias = 3 %, -6 %, and -7 %; NRMSE = 47 %, 53 %, and 118 % for altitudes between 40–500, 500–1500, and >1500 m, respectively) is quite good considering the challenging environment and few opportunities for assimilations of AOT from satellites during the campaign. Modeled relative humidities (RHs) are negatively biased at all altitudes (absolute bias =-5 %, -8 %, and -3 % for altitudes <500 500–1500 and >1500 m, respectively), motivating interest in the role of RH errors in AOT and extinction simulations. Interestingly, NAAPS-RA AOT and extinction agreement with the HSRL-2 does not change significantly (i.e., NRMSE values do not all decrease) when RHs from dropsondes are substituted into the model, yet biases all move in a positive direction. Further exploration suggests changes in modeled extinction are more sensitive to the actual magnitude of both the extinction coefficients and the dropsonde RHs being substituted into the model as opposed to the absolute differences between simulated and measured RHs. Finally, four case studies examine how model errors in RH and the hygroscopic growth parameter, γ, affect simulations of extinction in the mixed layer (ML). We find NAAPS-RA overestimates the hygroscopicity of (i) smoke particles from biomass burning in the Maritime Continent (MC) and (ii) anthropogenic emissions transported from East Asia. This work mainly provides insight into the relationship between errors in modeled RH and simulations of AOT and extinction in a humid and tropical environment influenced by a myriad of meteorological conditions and particle types. These results can be interpreted and addressed by the modeling community as part of the effort to better understand, quantify, and forecast atmospheric conditions in SEA.
This study uses airborne field data from the MONterey Aerosol Research Campaign (MONARC: northeast Pacific - summer 2019) and Aerosol Cloud meTeorology Interactions oVer the western ATlantic ...Experiment (ACTIVATE: northwest Atlantic - winter and summer 2020) to examine relationships between giant cloud condensation nuclei (GCCN) and cloud composition to advance knowledge of poorly characterized GCCN-cloud interactions. The analysis compares cloud water composition data to particle concentration data with different minimum dry diameters between 1 and 10 μm (hereafter referred to as GCCN) collected below and above clouds adjacent to where cloud water samples were collected. The northeast Pacific exhibited higher GCCN number concentrations above 1 μm, but with a sharper decline to negligible values at higher minimum diameters (5-10 μm) as compared to the northwest Atlantic. Vertical profiles of GCCN data revealed the larger influence of sea salt with major reductions above typical boundary layer heights for the two regions. Interrelationships between GCCN and cloud water composition revealed the following major conclusions: (i) sub-cloud GCCN data are better related to cloud water species concentrations in contrast to above-cloud GCCN data owing to overwhelming influence of sea salt relative to dust; (ii) GCCN number concentrations at the lowest (highest) minimum dry diameters were best related to cloud water sea salt concentrations for the northeast Pacific (northwest Atlantic) in part due to hardly any GCCN above 5 μm for the northeast Pacific; (iii) the northwest Atlantic exhibited stronger near-surface winds and turbulence linked to the enhanced levels of larger GCCN and the stronger relationship with cloud water sea salt levels; and (iv) linear regression models have marginal success in predicting cloud water sea salt levels. This study demonstrates feasibility in relating cloud water chemical data with supermicrometer particle data to tease out insights about GCCN-cloud interactions, with results relevant to designing future lab, modeling, and field studies.
Airborne field data are used to examine relationships between giant cloud condensation nuclei (GCCN) and cloud composition to advance knowledge of poorly characterized GCCN-cloud interactions.
Climate change is arguably the largest threat currently faced by all living things on Earth, and it is widely accepted that human activities have contributed considerably to global warming trends. ...Rising temperatures are largely driven by deviations in atmospheric properties relative to pre-industrial conditions, including changes in greenhouse gas budgets, aerosol particle properties and burdens, and cloud radiative properties. The complex ways in which modern anthropogenic behavior has and will continue to influence the planetary energy balance are uncertain yet highly urgent to resolve as humans continue to exploit Earth’s resources unsustainably and without comprehensive knowledge of the consequences. Anthropogenically-induced changes in aerosol particles and their relationships with clouds are the largest source of this uncertainty due to the highly transient nature of these atmospheric components and the challenges involved with routinely and globally observing and/or measuring their properties and interactions. The four research papers presented in this dissertation are motivated by the demand for improved understanding of aerosol particle and cloud properties, the complex and reciprocal interactions between particles and clouds, and the individual and synergistic impacts of particles and clouds on radiative forcing, specifically over marine environments which comprise the majority of Earth’s surface area. Each paper addresses a specific void in the literature using a combination of measurements and remote sensing retrievals obtained from ground stations and during airborne research campaigns taking place at a variety of marine locations around the world. These data were used to (1) validate and identify areas for improvement in simulations of aerosol optical properties in Southeast Asia from a chemical transport model, (2) understand the influence of various air mass types on cloud condensation nuclei concentrations at a site in coastal southeast Florida, (3) investigate the seasonality of sea salt reactivity over the northwest Atlantic (NWA) and examine the significance of quantifying this reactivity using absolute values as opposed to relative values, and (4) provide the first measurements of per- and polyfluoroalkyl substances (PFAS) in cloud water collected over the NWA across a range of seasons and to identify any air mass types particularly associated with the presence of PFAS in cloud droplets. Findings from these studies are beneficial for improving understanding of aerosol particle and cloud properties in and around polluted coastal and marine environments and their effects on climate and health.
Monitoring and modeling aerosol particle life cycle in Southeast Asia (SEA) is challenged by high cloud cover, complex meteorology, and the wide range of aerosol species, sources, and transformations ...found throughout the region. Satellite observations are limited, and there are few in situ observations of aerosol extinction profiles, aerosol properties, and environmental conditions. Therefore, accurate aerosol model outputs are crucial for the region. This work evaluates the Navy Aerosol Analysis and Prediction System Reanalysis (NAAPS-RA) aerosol optical thickness (AOT) and light extinction products using airborne aerosol and meteorological measurements from the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP.sup.2 Ex) conducted in 2019 during the SEA southwest monsoon biomass burning season. Modeled AOTs and extinction coefficients are compared to those retrieved with a high spectral resolution lidar (HSRL-2). Agreement between simulated and retrieved AOT (R.sup.2 = 0.78, relative bias =-5 %, normalized root mean square error (NRMSE) = 48 %) and aerosol extinction coefficients (R.sup.2 = 0.80, 0.81, and 0.42; relative bias = 3 %, -6 %, and -7 %; NRMSE = 47 %, 53 %, and 118 % for altitudes between 40-500, 500-1500, and 1500 m, respectively) is quite good considering the challenging environment and few opportunities for assimilations of AOT from satellites during the campaign. Modeled relative humidities (RHs) are negatively biased at all altitudes (absolute bias =-5 %, -8 %, and -3 % for altitudes 500 500-1500 and 1500 m, respectively), motivating interest in the role of RH errors in AOT and extinction simulations. Interestingly, NAAPS-RA AOT and extinction agreement with the HSRL-2 does not change significantly (i.e., NRMSE values do not all decrease) when RHs from dropsondes are substituted into the model, yet biases all move in a positive direction. Further exploration suggests changes in modeled extinction are more sensitive to the actual magnitude of both the extinction coefficients and the dropsonde RHs being substituted into the model as opposed to the absolute differences between simulated and measured RHs. Finally, four case studies examine how model errors in RH and the hygroscopic growth parameter, γ, affect simulations of extinction in the mixed layer (ML). We find NAAPS-RA overestimates the hygroscopicity of (i) smoke particles from biomass burning in the Maritime Continent (MC) and (ii) anthropogenic emissions transported from East Asia. This work mainly provides insight into the relationship between errors in modeled RH and simulations of AOT and extinction in a humid and tropical environment influenced by a myriad of meteorological conditions and particle types. These results can be interpreted and addressed by the modeling community as part of the effort to better understand, quantify, and forecast atmospheric conditions in SEA.
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