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The optical properties of carbonaceous aerosols were investigated to understand the impact source emissions and ambient particulate matter (PM) have on atmospheric radiative forcing. Black carbon (BC) is a strong absorber of visible light and contributes highly to atmospheric radiative forcing, therefore it is important to link BC properties to combustion emission sources. Brown carbon (BrC) is poorly understood and may be an important contributor to both positive and negative radiative forcing. The research investigates these primary knowledge gaps. The optical properties of carbonaceous aerosols were investigated to understand the impact source emissions and ambient particulate matter (PM) have on atmospheric radiative forcing. Black carbon (BC) is a strong absorber of visible light and contributes highly to atmospheric radiative forcing, therefore it is important to link BC properties to combustion emission sources. Brown carbon (BrC) is poorly understood and may be an important contributor to both positive and negative radiative forcing. The research investigates these primary knowledge gaps. Multiple methods were developed and applied to quantify the mass absorption cross-section (MAC) at multiple wavelengths of source and ambient samples. The MAC of BC was determined to be approximately 7.5 m2g−1 at 520nm. However, the MAC was highly variable with OC fraction and wavelength. The BrC MAC was similar for all sources, with the highest absorption in the UV at 370nm; the MAC quickly decreases at larger wavelengths. In the UV, the light absorption by BrC could exceed BC contribution by over 100 times, but only when the OC fraction is large (>90%) as compared to the total carbon. BrC was investigated by measuring the light absorption of solvent extracted fractions in water, dichloromethane, and methanol. Source emissions exhibited greater light absorption in methanol extractions as compared to water and DCM extracts. The BrC MAC was 2.4 to 3.7 m2g−1 at 370nm in methanol. Ambient samples showed similar MACs for the water and methanol extracts. Dichloromethane extracts did not have a significant light absorption characteristics for ambient samples. BrC and BC were measured in Beijing, China. Both were reduced significantly when restrictive air pollution controls were put in place. The industrial regions south and east of Beijing were the highest contributors to ambient BrC and BC. The controls reduced BrC more than BC as compared to observations during the regions heating period. Using the color characteristics of ambient PM, a model was developed to estimate elemental and organic carbon (EC/OC). The method will allow fast and cost effective quantification of PM composition in combination with large climate and health studies, especially in the developing world.
Air pollution, one of the most concerning and widespread environmental issues has grown in importance in the world. The carbonaceous aerosols significantly contribute to air pollution, which not only causes public health concern, but also impacts climate change. The aerosol particles have properties to absorb or scatter solar radiation and thermal radiation; therefore, they play an important role in climate change. In order to improve the understanding and control the aerosol particles, it is crucial to study aerosol size distribution and chemical compounds. Black carbon is the strongest radiative absorber suspends in the atmosphere, and can have great influence on climate change. This study investigates the size-selected black carbon optical properties under laboratory conditions with varied relative humidity referred to “dry”, “humid”, and “wet” respectively. The single scattering albedo that measures the relative amount of aerosol light extinction due to scattering, and the absorption enhancement due to lensing effect are measured in this study, and compared with the modeling results based on Mie theory, which is used to predict the absorption and scattering of light by a spherical particle. The results show that the single scattering albedo under the dry, humid, and wet conditions are similar, while the single scattering albedo for black carbon particles that have undergone heating to 160 oC is slightly greater than other three conditions. In general, with respect to particle size, single scattering albedo increases with smaller particle size and then levels off at larger size diameters. In addition, the absorption enhancement for black carbon particles is estimated in this study, and it ranges from 1 to 2.5. The values based on observations generally follow the predicted trend from Mie theory. Comparing the observed and modeled values suggests that 25%-50% of the total particle diameter is attributable to coating material. Dry black carbon particles do not have high absorption enhancement because they likely have no or thin coating materials. However, the absorption enhancement for humid particles and wet particles are higher than the dry particles, likely due to an enhanced lensing effect due to water uptake by the black carbon particles. Future study will focus on improving the understanding of black carbon optical properties and accuracy of experimental results. Further research is recommended to focus on ranges of BC particles with the diameters smaller than 100 nm and larger than 650 nm, which are not included in this study and constrain the particle charge units.
The concept of carbonaceous aerosol has only recently emerged from atmospheric pollution studies; even standard nomenclature and terminology are still unsettled. This monograph is the first to offer comprehensive coverage of the nature and atmospheric role of carbonaceous aerosol particles. Atmospheric chemists, physicists, meteorologists, and modellers will find this a thought-inspiring and sometimes provocative overview of all global phenomena affected by or related to carbonaceous aerosol.
Scientists have been observing a change in the climate since the beginning of the 20th century that cannot be attributed to any of the natural influences of the past. Natural and anthropogenic substances and processes perturb the Earth's energy budget, contributing to climate change. In particular, aerosols (particles suspended in air) have long been recognized to be important in processes throughout the atmosphere that affect climate. They directly influence the radiative balance of the Earth's atmosphere, affect cloud formation and properties, and are also key air pollutants that contribute to a variety of respiratory and cardiovascular diseases. Despite their importance, aerosol particles are less well-characterized than greenhouse gases with respect to their sources, temporal and spatial concentration distribution, and physical and chemical properties. This uncertainty is mainly caused by the variable and insufficiently understood sources, formation and transformation processes, and complex composition of atmospheric particles. Instruments that can precisely and accurately measure and characterize the aerosol physical and chemical properties are in great demand. Atmospheric relative humidity (RH) has a crucial impact on the particles' optical properties; the RH dependence of the particle extinction coefficient is an important parameter for radiative forcing and thus climate change modeling. In this work a Humidity-Controlled Cavity Ring-Down (HC-CRD) aerosol optical instrument is described and its ability to measure RH dependent extinction coefficients and related hygroscopicity parameters is characterized.
This book provides a synthesis of research findings, in terms of strategic knowledge outcomes regarding emergence of recent regional climate signals, implications for impacts assessment, and mitigation and adaptation response, relevant in the Indian context. The first part discusses evidence of climate change and its underlying scientific processes across India, chiefly focusing on impacts that are already visible and attributable to anthropogenic activities. The latter part deals with the responses to climate change, highlighting the mitigation and adaptation strategies in various sectors and communities. The book presents a concise interpretation, distilling practical recommendations and policy prescriptions at national and sub-national levels. It serves as a reference point for understanding scientific advances and persisting uncertainty, future vulnerability and response capacity of interlinked human and natural systems, pertaining to India. It is an excellent resource for policy makers and industry watchers in addition to the research fraternity.
Major factors that affect climate change depend on gas and particulate phase components in the atmosphere. Gas phase species have been studied in great detail and are well understood, causing a warming effect on the atmosphere. The less understood major contributing factor in the atmosphere are aerosol particles, which range in size from nanometers up to microns. Aerosol particles can directly scatter and absorb light and also have secondary effects such as acting as a surface for gas phase reactions to occur or seed particles for cloud formation. Aerosol particles can cause health problems ranging from serious cardiovascular to respiratory effects. All Climate and health effects of aerosol particles are dependent on particle composition, morphology, concentration, and size. Since a large variety of particulate types exist in the atmosphere, we have focused on understanding the effect of mineral dust composition and morphology. Mineral dust is important because it is the second largest emission by mass. In order to study the optical properties of aerosol particles, we built a cavity ring-down spectrometer and developed methods to interpret the excinction cross section results for particles with a varied shape. We have studied the major components of mineral dust that include calcium carbonate, hematite, quartz, aluminosilicate clay minerals, and feldspars, along with a heterogeneous dust sample. We have found that non-absorbing species that have surface roughness and an aspect ratio close to one (such as calcite, quartz and feldspar) can be treated as spheres. Aerosol particles that are absorbing (hematite) that have an aspect ratio near one with a roughened surface need to be treated with more complex models; otherwise the extinction cross section will be underrepresented. For aerosol particles that are non-absorbing but have a high aspect ratio (aluminosilicate clay minerals), additional modeling parameters are also needed that will account for shape and orientation. We have used Arizona Test Dust to determine if the models we have developed can be used to model the optical properties of a heterogeneous mixture. We have shown that the extinction cross section of the Arizona Test Dust can be modeled as long as individual components are treated independently and significant error would be introduces if all species were treated as spheres.Organic aerosol particles are chemically complex species that originate from primary or secondary emissions. We have described mixed organic/ammonium sulfate particles in the submicron regime using TEM to understand phase separation. When the organic component has a high aqueous solubility, all particles exhibit a homogeneous morphology while at low aqueous solubility all particles exhibit a phase separated structure. Intermediate solubility organics show a size dependent morphology. For pimelic and succinic acid, small particles (under approximately 200 nm) have a homogeneous structure while the larger particles exhibit phase separated structures. We have studied samples collected in Ulaanbaatar, Mongolia to better understand the types of particles and the effect of aging on these particles in an urban environment. The majority of the particles are soot, small spheres, or mineral dust. When we compared the monthly particle composition, we saw that there was an increased aging of the particles during the winter months due to pollution and a lower boundary layer leading to reduced atmospheric mixing. By understanding the particle composition present in areas and modeling the optical properties of individual particle types, better models can be created to give insight into aerosol particles affects on the atmosphere.
Urban aerosols have been identified as important species of concern due to their potential health and environmental impacts. This symposium series book will describe the basic chemistry and physics determining the impacts of aerosol species and will highlight the research results from the measurements that were taken following the collapse of the World Trade Center (WTC) on 9/11/01. The WTC tragedy led to the release of millions of pounds of debris aside from the structural steel, part of which was widely dissipated as aerosols and particulates in the debris cloud over lower Manhattan. Additionally, continuing fires under the debris led to the release of fine combustion related aerosols for a considerable time period in this urban environment. Held during the week of the second anniversary of the WTC tragedy in NYC, the symposium book will describe various aspects of the event, aerosol and gas exposures, and the related impacts of these aerosols. The book contributions will highlight efforts work from atmospheric chemists, meteorologists, health workers, and biologists for a timely compilation of what is known and not known about the composition and transport of tropospheric aerosols in urban environs, particularly those from the WTC collapse. Particular interest is in the acute and chronic environmental effects of these aerosols as they impact human health. Chapters included in the book will also address aerosol lifetimes, aerosol transport and removal processes, acute and chronic health effects to fine aerosol and particulate exposures, and the environmental impacts of aerosols.
The uncertainties in the aerosol effects on radiative forcing limit our knowledge of climate change, presenting us with an important research challenge. Aerosols in Atmospheric Chemistry introduces basic concepts about the characterization, formation, and impacts of ambient aerosol particles as an introduction to graduate students new to the field. Each chapter also provides an up-to-date synopsis of the latest knowledge of aerosol particles in atmospheric chemistry.