Research Interests

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My research group's interests are in the broad area of aerosol chemistry and analytical method development for atmospheric applications. Some specific directions include:

(1) 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 aerosol.

 

Current 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. 

 

(2) Optimizing quantification of bulk organic carbon fractions and elemental carbon

Organic carbon (OC) and elemental carbon (EC) in PM are most commonly differentiated and quantified using thermal/optical methods. However, charring of OC during thermal analysis causes difficulty in clean separation of EC and OC. We are interested in studying the factors impacting the OC charring, aiming to better quantify the differences of OC and EC concentrations obtained with different thermal/optical analysis protocols (e.g., IMPROVE, NIOSH, Ace-Asia protocols).

We are also interested in quantifying the sub-fractions of OC, such as water-soluble OC, and humic-like substances.

 

(3) Tracer-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, K+, 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.

 

(4) Exploring on-line measurements of PM chemical constituents for source apportionment and for probing atmospheric processes

On-line 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 EC and OC data (from real time aerosol carbon analyzer) and ionic composition data (from PILS and MARGA) for source analysis and process studies of the related PM components.

This page was last updated on 03/05/2016.