Enabling Routine Chemical Composition and Volatility Distribution Measurements of Aerosols

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.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Civil Engineering

Department dc:contributor.department

Civil and Environmental Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2025

Author dc:creator

• Kumar, Purushottam

Chair dc:contributor.committeechair

• Isaacman-VanWertz, Gabriel

Committee members dc:contributor.committeemember

• Marr, Linsey C.
• Foroutan, Hosein
• Hankey, Steven C.

• Aerosol composition
• instrumentation
• routine monitoring
• volatility distribution
• atmospheric chemistry

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:42414

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/124080