Author: Hwa Jin Kim Publisher: ISBN: Category : Languages : en Pages : 193
Book Description
The refractive index is the fundamental property controlling aerosol optical properties. Secondary organic aerosols (SOA) constitute a large fraction of aerosols in the atmosphere, and yet the optical properties of this complex material are just beginning to be understood. They appear to be much more variable than expected. We explore the factors controlling the real refractive indices (mr) of SOA under conditions that are as close to atmospheric conditions as possible. SOA were generated from the alpha-pinene, beta-pinene, limonene and toluene using several oxidation chemistries including ozonolysis with and without scavenger and photooxidation at different HC/NOx ratios, different mass concentration and experimental temperatures. Mr were retrieved from polar nephelometer measurements using parallel and perpendicular polarized 532 or 670 nm light where there is no evidence of significant absorption by the particles investigated here. Retrievals were performed with a genetic algorithm method using Mie-Lorenz scattering theory and measured particle size distributions. Overall examination of the SOA data shows that SOA mr ranges from 1.34 to 1.62, reflecting the factors to control the chemical composition; decreases as the HC/NOx ratio increases, decrease at lower temperature (
Author: Felisha Imholt Publisher: ISBN: Category : Aerosols Languages : en Pages : 102
Book Description
While the amount of solar radiation absorbed by greenhouse gases is known to a high certainty, the amount absorbed or reflected by secondary organic aerosols (SOA) is not. Our study aimed to discover how much radiation SOA particles absorb between ~200 and 800 nm.--
Author: Vanessa Selimovic Publisher: ISBN: Category : Atmospheric aerosols Languages : en Pages : 96
Book Description
"In this study, Fulvic Acid was used as a model to validate the experimental procedure for the analysis of several different samples of varying concentrations and compositions of SOA [secondary organic aerosols] generated by the oxidation of volatile organic compounds (VOC), specifically 1,2,4-trimethylbenzene." --
Author: Fathima Rifkha Kameel Publisher: ISBN: Category : Atmospheric aerosols Languages : en Pages : 86
Book Description
Aerosol particles (APs) affect the Earth's energy balance directly by absorbing and scattering radiation, and indirectly by altering the reflectance and persistence of clouds. Both parameters are determined by the chemical composition, size and shape of APs. APs consist of complex organic and inorganic mixtures, which include black carbon/soot as well secondary organic matter (SOM) proceeding from the gas-phase. SOM, also known as humic-like substances (HULIS), plays a key role in determining the optical properties of APs due to its ability to absorb radiation in the visible region of the solar spectrum. The chemical characterization of SOM is a daunting task that involves comprehensive chemical analysis, largely via chromatography/high-resolution mass spectrometry (HRMS), one of the most powerful analytical techniques available. However, optical properties are associated with chromophores within specific chemical structures, rather than with molecular formulas. Simpler mixtures can mimic the optical properties of secondary organic aerosol (SOA). Optical properties of mixtures are not linear combinations of the optical properties of its components. Furthermore, optical properties are not intrinsic to APs, but depend on external parameters, such as insolation and relative humidity. Therefore full speciation is neither a necessary nor sufficient condition for characterizing the optical properties of SOA.
Author: Dian Elizabeth Romonosky Publisher: ISBN: 9781369227819 Category : Languages : en Pages : 199
Book Description
A large fraction of organic aerosol particles are formed as secondary organic aerosol (SOA) resulting from the condensation of partially oxidized biogenic and anthropogenic volatile organic compounds (VOCs) with gas phase oxidants such as O3, OH, NOx, and NO3. An additional pathway for SOA formation is by the photochemical aqueous processing of VOC occurring inside cloud and fog droplets, followed by droplet evaporation. Once formed, SOA can age through heterogeneous oxidation and fog photochemical processes involving the hydroxyl radical (OH) as well as various other oxidants in the atmosphere. In addition to condensed phase oxidation, SOA can also age in the atmosphere upon exposure to radiation, for many of these organic compounds are photolabile and can degrade through direct photolysis, wherein the compounds absorb radiation and break into products, and indirect photolysis, wherein absorption of solar radiation initiates chemistry through the production of non-selective oxidants such as OH. These photochemical aging processes have the potential to be on time scales that are comparable to the typical lifetimes of droplets (hours) and particles (days), making them relevant to study further for both climate and health reasons. This dissertation presents a systematic investigation of the optical properties, molecular composition, and the extent of photochemical processing in different types of SOA from various biogenic and anthropogenic VOC precursors. Chamber- or flowtube-generated SOA is made and then analyzed using high-resolution mass spectrometry (HR-MS) to observe the extent of change in the molecular level composition of the material before and after aqueous photolysis. Significant differences in the molecular composition between biogenic and anthropogenic SOA were observed, while the composition further evolved during photolysis. To study the optical properties and lifetimes of organic aerosol, spectroscopy tools such as UV-Vis is utilized. Results of this study suggest that the condensed phase photolysis of SOA can occur with effective lifetimes ranging from minutes to hours, and therefore represents a potentially important aging mechanism for SOA. The outcome of this dissertation will be improved understanding of the role of condensed-phase photochemistry in chemical aging of aerosol particles and cloud droplets.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Summarizes the achievements of the project, which are divided into four areas: 1) Optical properties of secondary organic aerosols; 2) Development and of a polar nephelometer to measure aerosol optical properties and theoretical approaches to several optical analysis problems, 3) Studies on the accuracy of measurements of absorbing carbon by several methods, and 4) Environmental impacts of biodiesel.
Author: Jiumeng Liu Publisher: ISBN: Category : Aerosols Optical properties Languages : en Pages :
Book Description
The chemical and optical properties of particulate organic compounds remain unclear, which leaves large uncertainties in the estimation of global radiative transfer balance. Gas and find particle (PM2.5) phase formic acid concentrations were measured with online instrumentation during separate one-month studies in the summer of 2010 in Los Angeles (LA), CA, and Atlanta, GA, and the gas-particle partitioning behavior was investigated and compared with that of water-soluble organic compounds (WSOC). The diurnal profiles clearly indicated that the photochemistry production serves as a strong source for the formation of organics, while the correlation between the gas and particle phase suggested that another partitioning route, the aqueous reactions, is also very important. Later, the optical properties of light-absorbing organic compounds were examined. Little is known about the optical importance of light absorbing particulate organic compounds (brown carbon), especially its extent and absorption relative to black carbon throughout the tropospheric column. Mie theory was applied to size-resolved spectrophotometric absorption measurements of methanol and water-extracts from cascade impactor substrates collected at three surface sites around Atlanta, GA, including both urban and rural. These results were applied to similar measurements of brown carbon in extracts from aircraft bulk filter samples collected over central USA. At the surface sites predicted light absorption by brown carbon relative to total absorption (brown carbon plus pure black carbon) was about 10% and 30% at 350 nm, versus 1 and 11% at 450 nm, for water and methanol extracts, respectively. The relative contribution of brown carbon was greater in the free troposphere and significantly increased with altitude. Although this approach has limitations, it demonstrates the ubiquity and significant potential contribution of brown carbon.
Author: Hwa Jin Kim
Author: Felisha Imholt
Author: Vanessa Selimovic
Author: Fathima Rifkha Kameel
Author: Dian Elizabeth Romonosky
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Author: 
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Author: Miri Trainic
Author: Jiumeng Liu