Browsing by Subject "Aerosol"
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Item Embargo Characterization and modeling of aerosol-cloud interactions toward the improvement of rainfall estimation in high mountains(2023) Chavez, Steven PaulIn high elevated regions, ground-based precipitation measurements are scarce or non-existing. Remote sensing estimates are prone to underestimation due to a lack of sensitivity to light precipitation and ground-clutter contamination of radar signals by steep terrain. The latter creates a blind zone extending up a few kilometers above the ground for the vertical profiling radars onboard the Global Precipitation Measurement mission (GPM) core satellite that serves as a reference standard to unify precipitation measurements from research and operational satellites. Ground radars which are not affected by the blind zone, show an increase in effective reflectivity factor (ERF) from the melting layer below the isotherm of zero towards the surface. The blind zone is critical as rainfall characteristics at the ground results from the vertical evolution of the rain drop-size distributions (RDSDs). Explicit modeling of the rainfall microphysics from the top of the blind zone, if located below the zero-degree isotherm, towards the surface can improve rainfall estimation at the ground, as demonstrated in the Southern Appalachian Mountains. However, if the top of the blind zone is located above the zero-degree isotherm, ice and mix-phase hydrometeors coexist at the top boundary condition precluding explicit modeling because the microphysics of these hydrometeors is yet an active research topic. This work has three parts. The first part is devoted to characterizing precipitating systems and the blind zone in the Central Andes of Peru. Twenty years of TRMM and GPM radar measurements reveal that stratiform precipitation is the most frequent type in the Central Andes. Long-lasting precipitating systems (LDPSs) having a stratiform structure with embedded convection determine the interannual variability of the diurnal cycle of precipitation. Moisture availability at high elevations in the Central Andes is scarce. Moisture sources that sustain LDPSs are located in the adjacent eastern foothills of the Andes (Western Amazon basin) that result from enhanced moisture convergence and low and mid-levels due to the interplay of the South American low-level jet and cold air incursions. In the Central Andes of Peru, the top of the GPM blind zone is 46 % of the time above the zero-degree isotherm located at 5000 masl missing liquid precipitation, and a comparison with ground disdrometer data shows that GPM DPR does not capture the variability of the rain drop size distribution. These findings show that rainfall in the Central Andes depends on the dynamics of atmospheric circulation and microphysics at multiple spatial and temporal scales. These scales cannot be modeled explicitly by one single model nor validated with current observations. However, progress in that direction can be made by using different models to simulate different weather regimes to elucidate the role of different microphysics and dynamic processes. Observations needed to validate the models are lacking in the Andes but available in the Southern Appalachian Mountains (SAM). So, the modeling part of this work is focused on the SAM, and the knowledge gained by modeling the SAM region can be used to improve the representation of dynamical and microphysical processes in numerical models to be used in the Andes.Changes in the cloud drop size distribution ultimately capture the interplay of microphysics, dynamics, and thermodynamics in clouds. The chain of microphysical mechanisms from aerosol activation to cloud drop size distribution (CDSD) evolution during cloud development to the raindrop size distribution (RDSD) dynamics spans a scale range of four orders of magnitude from fractions of micrometers to millimeters. It can be modeled explicitly in cloud parcel and rain-shaft models (for liquid hydrometeors), and it is described using different parameterizations with varying degrees of complexity in Numerical Weather Prediction (NWP) models. However, in the Weather Research and Forecast (WRF) model, parameterized microphysics often fail to capture the diurnal cycle and spatial distribution of precipitation, rainfall intensity, and duration depending on the weather regime, regional topography, and regional aerosol characteristics. Besides, the representation of the dynamical processes affecting the aerosol activation and the CDSDs evolution during cloud formation and of the cloud-droplet-raindrop continuum in precipitating clouds is lacking in NWP models. In the second part of this work, a two-moment bulk microphysics scheme in WRF is modified to add an aerosol activation spectrum from in-situ measurement and compared to the default activation spectrum to characterize the impact of aerosol activation in the onset of precipitation in different weather conditions. WRF simulations show that using the in-situ aerosol activation spectrum yields higher cloud droplet number concentrations (CDNC) than the default WRF aerosol activation spectrum, with smaller cloud droplets and delayed onset of rainfall under weak synoptic forcing conditions. For large-scale systems with strong and sustained moisture convergence at low levels (frontal and tropical systems), mechanically forced rainfall efficiency is enhanced despite high CDNC, there is no delay in the onset of precipitation, and the impact of ACPI on the spatial and temporal variability of rainfall is negligible (significant) at onset (hours later) consistent with rainfall observations. The simulated cloud vertical structure from CDNC indicates that convective development is more intense in the inner SAM region than in the adjacent plains. In the inner region, valley-ridge circulations organize the spatial patterns of cloudiness under weak synoptic forcing conditions. The formation of early afternoon low-level clouds over the ridges in the summertime reflects the high sensitivity of cloud mixing ratios and cloud droplet concentrations to aerosol activation properties. In the third part of this work, the dynamical and microphysical processes not resolved by WRF are modeled using a large eddy simulation coupled with a spectrum bin microphysics that permits aerosol replenishment to characterize the heterogeneity of cloud microstructure associated with cloud circulations and entrainment in non-precipitating cumulus clouds. Furthermore, the sensitivity of cloud variables to different vertical profiles of aerosol loading is tested and validated with aircraft observations. The coupled model simulated a convective case under weak synoptic conditions, and the spatial variability of the LWC, CDNC, and CDSD was characterized. Simulations show large differences between the region around the updraft and regions of entrainment located at cloud edges and preferred locations. The interplay of environmental wind and cloud circulations explains these locations. More and larger droplets towards the location of the updraft and towards but before the cloud's top result in large LWC in the upper half of the cloud. The opposite in regions of entrainment, having small droplets in minor concentrations resulting in low LWC. Different initial vertical profiles of aerosol concentrations result in significantly different values of CDNC; as larger the aerosol loading, the larger the CDNC. The updraft transport aerosols and moisture up to the cloud altitude from near the ground elevation. In the updraft, a sharp CDSD with a small standard deviation has small values of relative dispersion. In regions of entrainment, the CDSD has smaller droplets in minor concentrations due to the evaporation of droplets. Its shape resembles the distribution of interstitial aerosols with a large standard deviation resulting in large values of relative dispersion and smaller values of LWC. Aircraft measurements show agreement with the simulated CDNC and relative dispersion for the simulation with an initial vertical profile of aerosol concentration that decays exponentially with height and has a scale height of 500m. The significant impact of aerosol loading in the CDNC affects the cloud optical thickness (COT). The COT in the cloud mature stage for a scale height of 2000m is approximately 1.75 times the COT for a scale height of 500m.
Item Open Access Digital Microfluidics for the Detection of Inorganic Ions in Aerosols(2018) Huang, ShuquanThe quantitative measurement of inorganic ions in the atmosphere is an important aspect in environmental science. The three most important inorganic ions are sulfate, nitrate and ammonium, which are the most abundant components of atmospheric pollutants and have a significant impact on rainfall, atmospheric visibility and human health. To accurately and quickly measure the distribution of inorganic ions in the vertical and horizontal directions of the atmosphere, a compact and automatic real-time detection system is in need.
The research performed in this study is aimed at developing the science and technology for an aerosol detection system that combines digital microfluidics technology, aerosol impaction and chemical detection on the same chip. The system will be smaller and faster with respect to current aerosol analyzing instruments. The chip in this study performs the integrated functions of aerosol collection, extraction, and quantitative detection in real-time, unlike current benchtop methods that require operator handling and laboratory equipment. All functions are realized in dedicated sections on a digital microfluidic platform.
This thesis will present the design and test of individual components of the aforementioned functions. The digital microfluidics chip design includes transparent top and bottom plates for light absorbance measurement. The droplets are dispensed, transported and mixed on chip with other droplets by activating electrodes individually with a 50V AC sine voltage.
In Chapters 3 and 4, the issues involving droplet transportation are addressed, including droplet movement between the air and silicone oil media and droplet transport across the aerosol impaction area. Next, an aerosol impactor and a chip-to-world chamber are demonstrated and tested with lab generated sulfate aerosol. The collected aerosol showed a clear pattern on the impaction plate, and the collection efficiency inside the chip was 96%.
In Chapter 5, the development of colorimetric methods are described as well as experimental testing for inorganic ion detection. Three well-known tests for detecting sulfate, nitrate and ammonium were first adjusted to adapt to on-chip measurement conditions, the adjustments including the choices of solvent, concentration ranges and mixing ratios. The particle measurement results using a conventional spectrometer were compared with on-chip measurements in terms of absorbance range, limit of detection, sensitivity (based on the coefficient of determination and the slope of the linear regression) and signal-to- noise ratio (presented with standard deviation/average of absorbance measurements).
The thin oil film between the droplet and the top/bottom plate, which is naturally formed, plays an important role in lubrication and reduces contact angle hysteresis. However, these oil films are not always uniform in thickness. During the absorbance measurement tests, varied sizes of oil lenses were observed at the oil/top plate interface, and the size and position of the oil lenses randomly changed when a droplet moved between electrodes. The absorbance measured in the normal direction to the chip’s surface was affected by these oil lenses and, thus, not stable for multiple measurements of the same droplet or for different droplets. To solve this problem, optical fibers were introduced horizontally inside the chip, and measurements taken in this direction proved to produce stable results.
Prototypes of the chip have been fabricated, and the impaction and on-chip colorimetric tests for sulfate and ammonium were successful. Although this study was designed to build the fundamentals of a novel detection system of inorganic ions in aerosol, the potential use of the designed system is not limited to atmospheric studies. Applications can extend to testing the quality of drinking water, detection of nitroaromatic explosives or other experiments based on colorimetry.
Item Open Access Forcing, Precipitation and Cloud Responses to Individual Forcing Agents(2020) Tang, TaoPreviously, we usually analyze climate responses to all the climate drivers combined. However, the climate responses to individual climate drivers are far from well-known, as it is nearly impossible to separate the climate responses to individual climate drivers from the pure observational records. In this dissertation, I analyzed the responses of effective radiative forcing (ERF), precipitation and clouds to five individual climate drivers by using the model output from the Precipitation and Driver Response Model Inter-comparison Project (PDRMIP, consisting of five core experiments: CO2x2, CH4x3, Solar+2%, BCx10, and SO4x5). Firstly, I compared the ERF values estimated by six different methods and demonstrated that the values estimated using fixed sea-surface temperature and linear regression methods are fairly consistent for most climate drivers. For each individual driver, multi-model mean ERF values vary by 10-50% with different methods, and this difference may reach 70-100% for BC. Then, I analyzed the dynamical responses of precipitation in Mediterranean to well-mixed greenhouse gases (WMGHGs) and aerosols and found that precipitation in Mediterranean is more sensitive to BC forcing. When scaled to historical forcing level, WMGHG contributed roughly two-thirds to the Mediterranean drying during the past century and BC aerosol contributed the remaining one-third by causing a northward shift of the jet streams and storm tracks. Lastly, I explored the responses of shortwave cloud radiative effect (SWCRE) to CO2 and the two aerosol species and found that CO2 causes positive SWCRE changes over most of the Northern Hemisphere during boreal summer, and BC causes similar positive responses over North America, Europe and East China but negative SWCRE over India and tropical Africa. When normalized by global ERF, the change of SWCRE from BC forcing is roughly 3-5 times larger than that from CO2. SWCRE change is mainly due to cloud cover changes resulting from the changes in relative humidity, and to a lesser extent, changes in circulation and stability. The SWCRE response to sulfate aerosols, however, is negligible compared to that from CO2 and BC, because the radiation scattered by clouds under all-sky conditions will also be scattered by aerosols under clear-sky conditions. As SW is in effect only during daytime, positive (negative) SWCRE could amplify (dampen) daily maximum temperature (Tmax). Using a multi-linear regression model, I found that Tmax increases by 0.15 K and 0.13 K given unit increase in local SWCRE under the CO2 and BC experiments, respectively. When domain-averaged, SWCRE changes contributed to summer mean Tmax changes by 10-30% under CO2 forcing and by 30-50% under BC forcing, varying by regions, which can have important implications extreme climatic events and socio-economic activities.
Item Open Access Surveillance for Swine Respiratory and Diarrheal Pathogens at the Human-Animal Interface in Sarawak, Malaysia(2017) Borkenhagen, Laura KimIntroduction: An estimated 75% of emerging infections in humans are zoonotic, posing a serious risk of future pandemics. The large livestock operations and dense human population of Southeast Asia are considered a hot-spot for the generation of novel viruses. The primary objective of this pilot study is to employ novel molecular laboratory analyses to examine evidence that swine pathogens including porcine circovirus 2, porcine rotaviruses, encephalomyocarditis virus, and porcine reproductive and respiratory syndrome virus, may be aerosolized at the animal-interface and that humans working in these environments may be carrying these viruses in their nasal airways.
Methods: This study took place in Sarawak, Malaysia among 11 pig farms, two slaughter houses, and three animal markets in June and July of 2017. Pig fecal, pig oral secretion, bioaerosol, and worker nasal wash samples were collected and analyzed via qRT-PCR for swine viruses. Workers were also surveyed for the nature of their occupational exposure with animals and their perceptions and use of personal protective equipment. Fisher’s Exact p-values and odds ratios were used to identify predictors of virus positivity.
Results: In all, 55 pig fecal, 49 pig oral or water, 21 bioaerosol, and 78 worker nasal wash samples were collected across 16 sites. Of these, 21 (38.2%) pig fecal, 43 (87.8%) pig oral or water, 3 (14.2%) bioaerosol, and 4 (5.1%) worker nasal wash samples were positive for PCV2 by qPCR. Porcine rotavirus C was detected in one (1.8%) pig fecal sample. No porcine rotavirus A or encephalomyocarditis virus was detected. The SYBR-based qRT-PCR assay used for PRRSv resulted in high levels of non-specific binding, omitting its inclusion in this write up. Statistically significant risk factors for PCV2 positivity among humans included having a household member with contact with pigs, farms with 1000 or more pigs, and a higher frequency of spotting rodents on the site. The personal protective equipment perceived as most effective at preventing cross-species infection and with the highest use were showering out of work and wearing dedicated boots. Among the equipment where use differed significantly from perception of efficacy were safety glasses, flu vaccination, showering out, and disposable boots.
Conclusions: Porcine circovirus has been posited as a zoonotic pathogen but limited studies have presented mixed results. Our data support the possibility of conducting a future prospective occupational study of pig workers for infection (not just nasal carriage) with this pathogen. Our data also shed light on contradictions between perception and use of personal protective equipment, stressing a need for education in farm biosecurity.