Enabling Routine Chemical Composition and Volatility Distribution Measurements of Aerosols
| dc.contributor.author | Kumar, Purushottam | en |
| dc.contributor.committeechair | Isaacman-VanWertz, Gabriel | en |
| dc.contributor.committeemember | Marr, Linsey C. | en |
| dc.contributor.committeemember | Foroutan, Hosein | en |
| dc.contributor.committeemember | Hankey, Steven C. | en |
| dc.contributor.department | Civil and Environmental Engineering | en |
| dc.date.accessioned | 2025-01-10T09:00:35Z | en |
| dc.date.available | 2025-01-10T09:00:35Z | en |
| dc.date.issued | 2025-01-09 | en |
| dc.description.abstract | Traditional online measurements of the chemical composition and other physicochemical properties (such as volatility and oxygenation) of particulate matter have relied on expensive and complex research-grade instrumentation based on mass spectrometry and/or chromatography. However, routine monitoring requires lower-cost alternatives that can be operated autonomously, and such tools are lacking. Routine monitoring of particulate matter, especially organic aerosol, relies instead on offline techniques such as filter collection that require significant operator effort. To address this gap, first, we built a new online semi-continuous aerosol chemical composition monitor, the "ChemSpot", that provides information on volatility-resolved organic carbon and degree of oxygenation along with sulfur content at relatively moderate costs. Autonomous operation of the ChemSpot instrument was demonstrated for four weeks alongside a mass spectrometer (an Aerosol Chemical Speciation Monitor, or ACSM), and the results of the comparison were encouraging. Mean absolute percentage errors (MAPE) were estimated to be 21% and 27% for aerosol organic carbon and equivalent sulfate (equivalent amount of sulfate for ChemSpot measured sulfur content). Chemspot-measured oxygen-to-carbon ratio (O:C) compared well with ACSM-measured O:C for moderate aerosol loadings. Second, we extended the capability of the ChemSpot instrument to provide volatility distributions of organic aerosols. A thermogram-based method was developed for the ChemSpot for volatility calibration and the calculation of volatility distributions. This work also highlighted the need for better observational constraints on vapor pressure values from structure-activity relationship based models. Finally, the ChemSpot was deployed at a biomass-burning experiment (Georgia Wildfire Simulation Experiment, G-WISE) to show the utility of this instrument in studying changes in volatility distributions of Biomass Burning Organic Aerosols (BBOA) produced from different biomass fuel types (samples from Blue Ridge and Coastal Plains eco-regions of the state of Georgia), different burn conditions (prescribed burning vs. wild burning) and simulated atmospheric aging. Significant changes in the volatility distributions of organic carbon were observed for the two biomass fuel types studied. Prescribed burning led to the formation of some higher volatility organic compounds in the aerosols compared to the wild burning case. A similar but more pronounced observation of the formation of higher volatility organics was observed after the simulated atmospheric aging of the BBOA samples. The formation of these higher volatility organics could be because of the presence of higher moisture content during the prescribed burning conditions. The successful completion of these objectives provides confidence that the ChemSpot could be a viable tool for long-term data collection of aerosol composition and volatility and in turn advancing aerosol science and helping policymakers devise strategies to curb air pollution. | en |
| dc.description.abstractgeneral | Aerosols are fine particles suspended in the air, either emitted directly or formed through chemical reactions in the atmosphere. A significant fraction of the aerosols is made of thousands of organic compounds, making it difficult to study their composition and properties. Aerosols have been found to have significant impacts on human health, atmospheric visibility, radiative balance, cloud formation and, climate change. These effects vary depending upon the composition of aerosols and their ability to remain in the particle phase or get vaporized to the gas phase (also known as volatility). Traditional automated measurements of aerosol composition and volatility often rely on either the direct use of complex research-grade instrumentation or offline measurements collecting samples on a filter followed by analysis utilizing the same research-grade instruments. These approaches can be extremely expensive and/or labor-intensive, often making collection of long term data unfeasible. Some lower-cost alternatives exist but do not provide enough information on aerosol chemical composition. Essentially, there is a lack of an automated aerosol composition monitor which can run without significant operator effort and provide valuable data at moderate costs. To address this need, first, we designed a new instrument "ChemSpot" that runs autonomously for extended periods of time. We also validated its performance against a time-tested research-grade instrument. Comparisons with the research-grade instrument were found to be satisfactory. Second, we developed a method to estimate the amount of organic carbon based on its ability to evaporate at different temperatures (termed volatility distribution). This work also highlighted the need to have better observational constraints on the vapor pressure data from different models accounting for the structure of these organic compounds. Finally, we deployed the ChemSpot instrument at a simulated wildfire experiment (Georgia Wildfire Simulation Experiment or G-WISE) to study the effects of different fuel types (samples from Blue Ridge and Coastal Plains eco-regions of the state of Georgia), different burn conditions (prescribed burning vs. wild burning) and simulated atmospheric reaction. Different fuel types and atmospheric reactions were found to have more significant effects on the aerosol composition and volatility distribution of the organic carbon. The successful completion of these objectives provides confidence that the ChemSpot instrument could be a viable tool for long-term data collection of aerosol composition and volatility and in turn advancing aerosol science and helping policy-makers devise strategies to curb air pollution. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:42414 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/124080 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Aerosol composition | en |
| dc.subject | instrumentation | en |
| dc.subject | routine monitoring | en |
| dc.subject | volatility distribution | en |
| dc.subject | atmospheric chemistry | en |
| dc.title | Enabling Routine Chemical Composition and Volatility Distribution Measurements of Aerosols | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Civil Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
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