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Developing more sensitive and simpler analytical methods for carbonaceous aerosol constituents

Airborne particulate matter (PM) is a major air pollutant in many urban areas. It is the main culprit in regional visibility reduction. Its association with increased morbidity and mortality has also been established by numerous epidemiological studies. Carbonaceous PM accounts for a significant fraction of the fine PM mass in many urban and nonurban areas, but what makes up organic aerosols is poorly understood. Lack of molecular level chemical composition hinders our ability to adequately predict the climatic and health effects of aerosols.

Currently methods are only able to identify and quantify at most one-third of the organic materials associated with particles at a molecular level. Much of the unidentified mass is polar in nature. We use ultra-high resolution mass spectrometry to expand the list of identified organic compounds. In the same time, we strive to develop LC-MS methods and methods using derivatization in conjunction with GC-MS analysis for quantification.

Many conventional analytical methods are laborious, which practically limits the number of samples that can be analyzed. We also target to develop simpler analytical methods. For example, we have developed in-injection port thermal desorption GCMS methods (TD-GCMS) for polycyclic aromatic hydrocarbons (PAHs) and other nonpolar aerosol organics. The TD-GCMS method greatly shortens and simplifies the chemical analyses, permitting the process of hundreds of samples for source apportionment studies.

Online measurements of PM chemical constituents for source apportionment of PM and for probing atmospheric processes

Online measurements of PM constituents are most suitable to capture the dynamic features of emission sources and atmospheric processes through higher time resolution data coverage. We use real-time OC and EC data (from semi-continuous aerosol carbon analyzer), ionic composition data (from MARGA), metals (from online XRF), and organic molecular tracers (from TAG) for source analysis and process studies of the related PM components.

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Traced-based receptor modeling for source apportionment of PM

Receptor models take ambient measurements of PM constituents as input to apportion major contributing sources, providing field observation-based source information for comparison with results from emissions-based air quality models. We quantify a wide range of source tracers from elements (e.g. Ni and V for residual oil combustion, Si, Fe, Al, and Ti for suspended dust particles) to inorganic ions (e.g. sulfate, nitrate, ammonium, water-soluble potassium ion, etc.) to organic tracers for secondary and primary organic aerosols (e.g. levoglucosan for biomass burning, hopanes for fossil fuel uses, methyl tetrols for tracking isoprene SOA, organic sulfates for SOA from sulfation processes, etc.). We explore the optimal use of two types of receptor models, chemical mass balance (CMB) and positive matrix factorization (PMF), for apportioning PM sources.

Instrumental determination of bulk inorganic nitrogen and organic nitrogen in aerosol samples

Nitrogenous aerosols are ubiquitous in the atmosphere, serving as a significant source of supplementary nutrition for ecosystems after deposition. They also contribute to a sizable fraction of aerosol mass, impacting visibility and affect global and regional climate. Chemically, they fall into two groups, i.e, inorganic nitrogen (IN) and organic nitrogen (ON). While aerosol IN mainly consists of ammonium (NH4+) and nitrate (NO3-) and their atmospheric abundance and chemistry are largely established, aerosol ON is hugely complex in its molecular composition and the total ON quantity is almost un-characterized. This leaves an important data gap in quantifying the various roles that aerosol ON plays in our atmospheric environment and ecosystems. We are developing an aerosol C, ON & IN analyzer that enables direct and simultaneous measurements of carbon content, ON and IN in filter-based aerosol samples.

Assessment of oxidative potential of PM by acellular assays

One important underlying cause of the adverse health effects induced by PM is excessive oxidative stress. Ambient PM, once inhaled into the lung fluid, is capable of consuming antioxidants (e.g. ascorbic acid (AA) and glutathione (GSH)) and producing reactive oxygen species (ROS) (i.e., hydroxyl radical, hydrogen peroxide, and superoxide radical). This ability to deplete antioxidants or generate ROS is termed as oxidative potential (OP). We are interested in quantifying the link between OP and active components in PM (e.g., metals, certain organic compounds), and apportioning OP into major PM sources.