Research Areas and Project Showcases

Dr. Du’s research has been focused on developing innovative technologies to address the most challenging issues in the field of urban air pollution as well as answering some of the most interesting questions on the impact of urbanization on global and regional atmospheric environment. His primary research interests include optical remote sensing of air pollutants, source apportionment of carbonaceous aerosols, measurement of aerosol and black carbon (BC) emissions and modeling of their radiative forcing effects. Below is a summary of research activities along the directions of air pollution process and environmental monitoring techniques.

Air pollution process

In this direction, Dr. Du’s research is focused on black carbon, haze, visibility, and other air quality indices addressing the issues on how rapid urbanization poses negative impact on the natural environment, and what may be cost-effective mitigation strategies from the perspective of policy-makers. For carbonaceous aerosol studies, he investigated the sources of black carbon in East Asia, studied the emission and transport of carbonaceous aerosols and the light absorbing properties of black carbon aerosols. The approaches that were taken incorporated both field measurement and mathematical modeling of the ambient and source aerosols. Such work not only builds up our knowledge in understanding the characteristics of air pollution, but serves to advise the regulatory authorities for solving challenges associated with the pollutants. For regional haze and visibility, he studied the long-term variation of visibility in Southeast China, analyzed the impact of several environmental policies on regional haze, and determined the efficacy of different policies in mitigating air pollution problems, and investigated the impact of meteorological factors on atmospheric visibility at a coastal urban site.

Environmental monitoring techniques

Dr. Du has devoted years in developing innovative optical and/or remote sensing technologies to measure pollutants or environmental pollution indices. This include: I) quantify the opacity of airborne particulate matters (PM) over elevated spatial and temporal scales. Opacity is an important optical property that is used by the environmental authorities to determine compliance for visible emissions from industrial sources. He invented a digital photography based method (DOM) to quantify the opacity of PM plumes from industrial point sources, which was awarded a US patent in 2008. The Office of Air Quality Planning and Standards (OAQPS) of the United States Environmental Protection Agency (USEPA) estimated that the digital camera based technology could save 200 million US dollars annually if implemented country-wide in the US; II) Apply innovative LIDAR technologies for development of methodologies to quantify PM emissions from fugitive sources, which are more important and more difficult-to-quantify. This method provides a novel approach to quantify the emissions of fugitive dust by developing an algorithm that integrates the measurements from LIDAR, Laser Transmissometers, and Fourier Transform Infrared Spectrometers to determine the mass fluxes of dust. This work was appraised (http://www.serdp.org/content/download/8726/106111/file/RC-1400-FR.pdf) by SERDP (Strategic Environmental Research and Development Program) under the US DoD (Department of Defense) and received “Research, Development, or Operational Support Team Award” from U.S. Army in 2008; III) Develop cost-effective methods for monitoring black carbon aerosol; and IV) Develop digital photographic method to quantify atmospheric visibility.

ORS-based hybrid methane emission mapping system

Methane emissions from fugitive areas sources present challenges to emission reduction technologies for their heterogeneity, large spatial scale, and highly variable fluxes. Conventional technologies, such as flux chamber method (FC), eddy covariance technique (EC), flux tower technique (FT), and upwind/downwind sampling (UD), have difficulties in measuring emissions from large-scale, heterogeneous, fugitive sources at remote sites with harsh weather conditions as they either assume homogeneous flux (FC), or only capture a limited portion of the plume (FT, UD) which cause the representativeness of the results to be questionable, or have strict restrictions on terrain and turbulence conditions (EC). In order to address the urgent need for accurate measurement of methane, it requires ready-to-deploy solutions to locate and quantify emission hot spots and fluxes so that actions can be immediately taken to effectively reduce methane emissions in a technically achievable and economically sustainable manner. Also, knowing the quantity of fugitive methane emission can help us evaluate of performance of methane emission reduction techniques for fugitive area sources.

The project we are working on is to develop a hybrid system by integrating the 2-D concentration profiles from ORS radial plume mapping (RPM) results with backward dispersion model to generate real-time emission flux distribution over large, heterogeneous fugitive sources,  so that the total emission can be quantified and the emission hot spots can be located. 

Advantages of the system over traditional ones are:

• It is fast and in real time (compare to human survey using hand-held sensors)
• It is automatic and can monitor for long time (days to weeks) (compare to surveys by human, vehicles, or UAV)
• It can find and locate the emission hot spots (human, vehicle, or UAV surveys find concentration hot spots but they may not be the emission hot spots depending on wind conditions).
• It can quantify emission for heterogeneous area sources (compare to flux chamber technique).

Field testing for this system could be found at our YouTube channel: Field Testing

Characterizing ozone and SOA formation potentials from volatile organic compounds (VOCs) emissions in an oil industry center in Canada

Past source apportionment studies focused on the contribution to VOC concentration from different sources to pinpoint the major VOC sources for emission mitigation. However, different VOC sources may have different ozone and secondary organic aerosol (SOA) formation potentials. So, from control perspective, it would be more rationale to consider the role of individual VOC source in secondary pollution in source apportionment study. In this study, we propose a tiered source identification method that considers the formation potentials of ozone and SOA and applied it in Calgary, Alberta, a site under influence from multiple competing VOC sources. The pollution characteristic, secondary pollutant formation potential, and geographical origin of VOC sources were explicitly investigated over a five-year period. Seven major sources were identified using positive matrix factorization (PMF) model, among which vehicle exhausts and fuel combustion were the dominant VOC sources responsible for the O (60%) and SOA (63%) formations, suggesting that combustion of both liquid fuel (vehicle exhaust) and solid fuel (fuel combustion) has exceeded the contribution from oil and gas production and become the top contributor to ozone and aerosol pollution in Calgary. This finding was consistent with the fact of great reductions (32.2% - 99.8%) in oil and gas production in Calgary from 2013 to 2017. The source apportionment results showed that the primary VOC source has shifted from conventional oil and gas extraction to a mixture of vehicle exhausts and oil and gas extraction, indicating the effectiveness of emission control measures taken in the energy sectors. Moreover, regional transported VOC from combustion sources in the southeastern British Columbia, greatly deteriorated the VOC level and secondary pollutants formation in Calgary. To effectively alleviate secondary pollution problems, it was recommended to perform joint pollution control measures by the Alberta and British Columbia governments. These findings revealed that the tiered source identification strategy combining traditional receptor model with socioeconomic factors, emission inventory, and source region analysis, was a robust and promising tool in the interpretation of source apportionment results and optimization of secondary pollution control.

Virtual presentation can be found here.

Near Infrared Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (NIR-IBBCEAS)

The efforts for reducing carbon emissions by switching from coal to natural gas have created a bigger threat to global warming through natural gas leaks. Apart from the monetary losses, leakage of natural gas releases methane, which can trap more than 80 times as much heat as carbon dioxide. Most often, the leaks are left unmonitored due to the huge cost and clumsy nature of existing leak detection techniques. The main competition is between the rate of false alarms and cost-effectiveness. 

Incoherent broadband absorption spectroscopy (IBBCEAS) is a cavity-enhanced absorption spectroscopy technique that has been in use to sensitively detect trace pollutants for past decade. This is a very sensitive technique and has been applied from selected bands in the UV to visible spectral regions (UV-Vis) by using the arc lamp or LED as the light source. However, application of this technique in the NIR regions are much desired due to the fingerprint absorption lines for many molecules and less interference from water vapor and aerosol scattering. Thanks to the recent development of high-power super-continuum light sources, we was able to test the feasibility of using IBBCEAS in NIR region for detecting the major component of natural gas, e.g., methane, ethane, propane, and butane, who  have distinct absorption bands in the spectrum of 1100nm-1250nm.

• In this project, we designed and developed a working prototype of NIR-IBBCEAS for detecting the major components of natural gas with the following features:
• It could be used as a detector for the individual leak detection of methane, butane, ethane or propane leaks or that of hydrocarbon mixtures containing any combinations of the above gases.
• It could serve the purpose of testing the quality of a natural gas mixture.
• Natural gas leak detection is less prone to false alarm as it simultaneously monitor the major hydrocarbon components of the gas over a broad range of wavelength.
• It suites the purpose of a cheaper continuous long-time monitoring of gas leak over a region rather than the occasional costlier flight measurements.