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This dissertation describes the use of measured aerosol size distributions and size-resolved hygroscopic growth to examine the physical and chemical properties of several particle classes. The primary objective of this work was to investigate the optical and cloud forming properties of a range of ambient aerosol types measured in a number of different locations. The tool used for most of these analyses is a differential mobility analyzer / tandem differential mobility analyzer (DMA / TDMA) system developed in our research group. To collect the data described in two of the chapters of this dissertation, an aircraft-based version of the DMA / TDMA was deployed to Japan and California. The data described in two other chapters were conveniently collected during a period when the aerosol of interest came to us. The unique aspect of this analysis is the use of these data to isolate the size distributions of distinct aerosol types in order to quantify their optical and cloud forming properties. I used collected data during the Asian Aerosol Characterization Experiment (ACE-Asia) to examine the composition and homogeneity of a complex aerosol generated in the deserts and urban regions of China and other Asian countries. An aircraft-based TDMA was used for the first time during this campaign to examine the size-resolved hygroscopic properties of the aerosol. The Asian Dust Above Monterey (ADAM-2003) study was designed both to evaluate the degree to which models can predict the long-range transport of Asian dust, and to examine the physical and optical properties of that aged dust upon reaching the California coast. Aerosol size distributions and hygroscopic growth were measured in College Station, Texas to investigate the cloud nucleating and optical properties of a biomass burning aerosol generated from fires on the Yucatan Peninsula. Measured aerosol size distributions and size-resolved hygroscopicity and volatility were used to infer critical supersaturation distributions of the distinct particle types that were observed during this period. The predicted cloud condensation nuclei concentrations were used in a cloud model to determine the impact of the different aerosol types on the expected cloud droplet concentration. RH-dependent aerosol extinction coefficients were also calculated.
Aerosols can interact with radiation directly through scattering and absorption and indirectly by serving as cloud condensation nuclei. The uncertainty of how particles and clouds interact with radiation is still high amidst the progress made in recent years, which hinders our current understanding of how these particles affect the Earth’s radiation budget. This works aims to reduce this uncertainty by targeting the two most light-absorbing atmospheric particles, mineral dust and black carbon, and study how they interact with radiation, how they serve as cloud condensation nuclei, assessing popular measurement techniques and evaluating their impact in two different tropical forest ecosystems. Field measurements were carried out in the Caribbean island of Puerto Rico and in the Brazilian Amazon. In Puerto Rico, aerosol-cloud interactions were studied in the tropical montane cloud forest (TMCF) of Pico del Este, which receives consistently during summer months the influence of mineral dust from the Sahara/Sahel region in Africa (i.e., African dust). In Brazil, specifically in the Amazon basin, measurements of black carbon were performed in the city of Manacapurú, an area exposed to the influence of urban and biomass burning pollution. At Pico del Este, periods of low and high dust influence were identified through the use of aerosol optical properties, and air mass trajectories (HYSPLIT). It was found out that African dust interacts with clouds and produces a higher number of droplets, but the mean droplet effective diameter is not significantly altered. Similarly, the deposition of water and nutrients through water and clouds was studied, and results suggests that rain is the main mechanism through where water is deposited to the ecosystem over clouds (58- 78%). Cloud water presented an enrichment of nutrients over rainwater, suggesting that clouds are more important than rain for supplying TMCFs with nutrients. At the Brazilian Amazon basin, an Aethalometer -the most popular technique for measuring black carbon concentrations through the absorption coefficient- was used and several corrections used to overcome known artefacts for this type of measurements were evaluated. Results suggests that this technique can overestimate the absorption coefficient by a factor of 5 and that the corrections do not agree well among each other.
Life on Earth is critically dependent upon the continuous cycling of water between oceans, continents and the atmosphere. Precipitation (including rain, snow, and hail) is the primary mechanism for transporting water from the atmosphere back to the Earth’s surface. It is also the key physical process that links aspects of climate, weather, and the global hydrological cycle. Changes in precipitation regimes and the frequency of extreme weather events, such as floods, droughts, severe ice/snow storms, monsoon fluctuations and hurricanes are of great potential importance to life on the planet. One of the factors that could contribute to precipitation modification is aerosol pollution from various sources such as urban air pollution and biomass burning. Natural and anthropogenic changes in atmospheric aerosols might have important implications for precipitation by influencing the hydrological cycle, which in turn could feed back to climate changes. From an Earth Science perspective, a key question is how changes expected in climate will translate into changes in the hydrological cycle, and what trends may be expected in the future. We require a much better understanding and hence predictive capability of the moisture and energy storages and exchanges among the Earth’s atmosphere, oceans, continents and biological systems. This book is a review of our knowledge of the relationship between aerosols and precipitation reaching the Earth's surface and it includes a list of recommendations that could help to advance our knowledge in this area.
This two-volume set provides an extensive review of the abundant past and recent literature on the atmospheric chemistry in the Mediterranean region. The books document the experience gained on the atmospheric composition over the Mediterranean basin and close areas after six decades of research, starting from early studies of radioactive aerosol fallouts and intense desert dust events in the 1960s, followed by studies of aerosols collected during oceanographic cruises in the early 1980s, and including subsequent knowledge from various surface monitoring stations, intensive campaigns, satellite climatologies, laboratory studies, as well as chemistry-transport and climate models. Through ten thematic sections, the authors examine the sources and fates of atmospheric pollutants over the Mediterranean basin and what we know about the main impacts of the regional atmospheric chemistry. This overview not only considers the full regional cycle of both aerosol and reactive gases including emissions, transport, transformations, and sinks, but also addresses their major impacts on air quality and health, on the radiative budget and climate, on marine chemistry and biogeochemistry . The volumes are an initiative from the ChArMEx project that has federated many studies on those topics in the 2010-2020decade, and update the scientific knowledge by integrating the ChArMEx and non-ChArMEx literature. The books are contributed by a large pool of well-known authors from the respective fields, mainly from France and Greece, but also from six other Mediterranean and eight non-Mediterranean countries. All Chapters have been peer-reviewed by international scientific experts in the corresponding domains. Volume 2 focuses on emissions and their sources, recent progress on chemical processes, aerosol properties, atmospheric deposition, and the impacts of air pollution on human health, regional climate and ecosystems. Recommendations for future research in these fields are finally proposed. The targeted audience is the academic community working on atmospheric chemistry and its impacts, especially teams having a special interest in the Mediterranean region, which includes many countries and institutes worldwide.
The National Research Council's Committee on Atmospheric Chemistry (NRC/CAC) was established to serve as a focal point for NRC activities on issues related to atmospheric chemical change and its impacts on air quality, climate, stratospheric ozone depletion, and other related issues. The committee consists of 12 members with expertise covering the areas of tropospheric and stratospheric chemistry; urban/regional air pollution; modeling of climate, chemistry, and atmospheric dynamics; in situ and remote sensing observational systems; and interfaces of science and public policy. This CAC study was motivated by a concern that, in the coming decades, dramatic increases in global population and urbanization levels, as well as changes in global climate, may significantly affect air quality over large regions of the globe. The charge to the committee was to examine the linkages among regional/ global changes in atmospheric composition, climate change, and air quality.
This edited volume sheds new light on the impact of rapid Land Use/Cover Changes (LU/CC) on greenhouse gases (GHG’s) and aerosol emissions in South and Southeast Asia. Several countries in South/Southeast Asia have the highest population growth rates in the world, which is the main cause for LU/CC. Conversion of dense forests to agricultural areas and then to residential and urban areas is most commonly observed in South/Southeast Asian countries with a significant release of GHG’s and aerosols. The book showcases several case studies on the use of remote sensing and geospatial technologies to quantify biomass burning and air pollution impacts, aerosol pollution, LU/CC, and impacts on ecosystem services. The book also includes articles on regional initiatives in research, capacity building, and training. The authors of this book are international experts in the field, and their contributions highlight significant drivers and impacts of air pollution in South/Southeast Asia. Readers will discover the latest tools and techniques, in particular, the use of satellite remote sensing and geospatial technologies for quantifying GHG’s, aerosols and pollution episodes in this region.
Atmospheric aerosol particles are a major component of the troposphere and affect regional and global atmospheric chemistry and climate. The size and chemistry of these particles influences the warm and cold cloud nucleation ability and optical properties of the aerosol particles. This dissertation investigates the atmospheric chemistry of aerosol particles and their role in warm cloud nucleation through a combination of laboratory experiments and field measurements. The effect of organics on the cloud condensation nuclei (CCN) activity of sea spray aerosols is described in Chapter 2. Sea spray aerosol produced by bubbling solutions composed of simplistic mixtures of NaCl and oleic acid or SDS had a significant effect on CCN activity, even in very small amounts; while artificial seawater solutions containing microorganisms, the common cyanobacteria (Synechococcus) and DMS-producing green algae (Ostreococcus), produced particles containing ~34 times more carbon than the particles produced from pure ASW, with no significant change observed in the overall CCN activity. During the fall of 2007 and 2008, over 300,000 acres burned in San Diego County wildfires. The resulting particle chemistry and estimated hygroscopicity during these wildfire events are explored in Chapter 3. The contribution of wildfire emissions were much larger and played a more significant role in affecting cloud condensation nuclei and total particle concentrations in 2007 than in 2008. The overall particle hygroscopicity during the biomass burning dominated periods was very similar; however in 2008, the particle hygroscopicity was dominated by local sources rather than biomass burning, due to the much smaller particle size mode. Owens Lake is one of the largest sources of PM2.5 in the Western Hemisphere, producing highly soluble dust plumes, and therefore there is great potential for those particles to impact cloud formation and possibly precipitation in the region. Chapter 4 explores particle chemistry and estimated hygroscopicity at Owens Lake. No significant change in particle hygroscopicity or CCN activity occurred concurrently with the change in mixing of particle classes during two different dust events at Owens Lake; indicating that the large dust particles were most likely completely CCN active and the smaller particles are likely dictating the hygroscopicity, as most of the dust particles are large enough and would activate to become CCN regardless of their hygroscopicity. The Cloud Indirect Forcing Experiment (CIFEX) took place to study the influence of aerosols on cloud properties at Trinidad Head, a coastal site in northern California representing clean marine air with periodic long-range transport. Chapters 5 & 6 explore particle chemistry, mixing state, optical properties and estimated hygroscopicity during CIFEX. Our measurements demonstrate how changes in hygroscopicity and optical properties evolve over time in the atmosphere as a function of particle chemistry and the mixing state of the aerosol. Two distinct oxalate events with enrichment of oxalate on different particle types and sizes suggest two separate sources of oxalate.