Theses and Dissertations from UMD
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Item Multi-instrument approach for measuring spectral aerosol absorption properties in UV and VIS wavelengths(2017) Mok, Jungbin; Li, Zhanqing; Krotkov, Nickolay A.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The spectral dependence of light absorption by atmospheric particulate matter (PM) has major implications for air quality, surface ultraviolet (UV) radiation, and tropospheric oxidation capacity, but remains highly uncertain. Quantifying the spectral dependence of aerosol absorption at UV and visible wavelengths is important for the accurate air pollution characterization using current (e.g., Aura/OMI) and future (e.g., TROPOMI, TEMPO, GEMS) satellite measurements, photolysis rates calculations in chemical and aerosol transport models and surface radiation modeling. Measurements of column atmospheric absorption and its spectral dependence remain the most difficult part of atmospheric radiation measurements. Currently available ground measurements of spectral aerosol absorption properties (e.g., column effective imaginary refractive index (k), single scattering albedo, (SSA), and aerosol absorption optical depth (AAOD)) are limited to the cloud free conditions and few discrete wavelength bands in the visible spectral region by AERONET almucantar inversions. To address the lack of spectral aerosol and gaseous absorption measurements in the UV, a suite of complementary ground-based instruments, modified UV Multifilter Rotating Shadowband Radiometer (UV-MFRSR) was established in 2002 and is currently in use at NASA Goddard Space Flight Center (NASA/GSFC) in Greenbelt, Maryland. In addition, several field campaigns have been carried out to measure aerosol absorption properties in UV and VIS from different sources in different locations. In September-October 2007 biomass-burning season in the Amazon basin (Santa Cruz, Bolivia), light absorbing (chromophoric) organic or “brown” carbon (BrC) is studied with surface and space-based remote sensing. It is found that BrC has negligible absorption at visible wavelengths, but significant absorption and strong spectral dependence at UV wavelengths. Using the ground-based inversion of column effective imaginary refractive index (k) at UV wavelengths down to 305 nm, a strong spectral dependence of specific BrC absorption is quantified in the UV implying more strongly reduced ultraviolet B (UV-B) radiation reaching the surface. Reduced UV-B means less erythema, plant damage, but also a slower ozone photolysis rate. A photochemical box model is used to show that relative to black carbon (BC) alone, the combined optical properties of BrC and BC slow the net rate of production of ozone by up to 18% and lead to reduced concentrations of radicals OH, HO2, and RO2 by up to 17%, 15%, and 14%, respectively. The optical properties of BrC aerosol change in subtle ways the generally adverse effects of smoke from biomass burning. The objective of this thesis is to develop a new method to infer column effective spectral absorption properties (k, SSA, and AAOD) of PM using the ground-based measurements from AERONET in the visible wavelengths and UV-MFRSR in the UV and ozone and NO2 from ground-based (Pandora and Brewer) or satellite spectrometers, such as Ozone Monitoring Instrument (OMI) on NASA EOS Aura satellite. This represents the first effort to separate effects of gaseous (ozone and NO2) and aerosol absorption and partition black and brown (light-absorbing organic) carbon absorption in the short UV-B wavelengths. These measurements are essential to answer key science questions of the atmospheric composition and improve data products from the current and future satellite atmospheric composition missions.Item A STUDY OF REMOTELY SENSED AEROSOL PROPERTIES FROM GROUND-BASED SUN AND SKY SCANNING RADIOMETERS(2012) Giles, David Matthew; Dickerson, Russell R; Thompson, Anne M.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol particles impact human health by degrading air quality and affect climate by heating or cooling the atmosphere. The Indo-Gangetic Plain (IGP) of Northern India, one of the most populous regions in the world, produces and is impacted by a variety of aerosols including pollution, smoke, dust, and mixtures of them. The NASA Aerosol Robotic Network (AERONET) mesoscale distribution of Sun and sky-pointing instruments in India was established to measure aerosol characteristics at sites across the IGP and around Kanpur, India, a large urban and industrial center in the IGP, during the 2008 pre-monsoon (April-June). This study focused on detecting spatial and temporal variability of aerosols, validating satellite retrievals, and classifying the dominant aerosol mixing states and origins. The Kanpur region typically experiences high aerosol loading due to pollution and smoke during the winter and high aerosol loading due to the addition of dust to the pollution and smoke mixture during the pre-monsoon. Aerosol emissions in Kanpur likely contribute up to 20% of the aerosol loading during the pre-monsoon over the IGP. Aerosol absorption also increases significantly downwind of Kanpur indicating the possibility of the black carbon emissions from aerosol sources such as coal-fired power plants and brick kilns. Aerosol retrievals from satellite show a high bias when compared to the mesoscale distributed instruments around Kanpur during the pre-monsoon with few high quality retrievals due to imperfect aerosol type and land surface characteristic assumptions. Aerosol type classification using the aerosol absorption, size, and shape properties can identify dominant aerosol mixing states of absorbing dust and black carbon particles. Using 19 long-term AERONET sites near various aerosol source regions (Dust, Mixed, Urban/Industrial, and Biomass Burning), aerosol absorption property statistics are expanded upon and show significant differences when compared to previous work. The sensitivity of absorption properties is evaluated and quantified with respect to aerosol retrieval uncertainty. Using clustering analysis, aerosol absorption and size relationships provide a simple method to classify aerosol mixing states and origins and potentially improve aerosol retrievals from ground-based and satellite-based instrumentation.