[Seminar] Dr. Yongjoo Choi

Regional variability in black carbon and carbon monoxide ratio from long-term observations over East Asia: assessment of emission inventories and wet removal scheme

The ability to obtain accurate emission estimates of greenhouse gases (GHGs) has been highlighted as an important issue for many decades, not only for regulating local air quality but also for assessing national-scale air quality and climate concerns. In particular, urban emissions need to be well-understood because approximately 70% of anthropogenic greenhouse gas emissions originate from urban areas. Emission of carbon dioxide (CO2) and methane (CH4) and the meteorological factors affecting them using an aircraft equipped with a cavity ring-down greenhouse gas sensor as part of the Alpha Jet Atmospheric eXperiment (AJAX) project flights in a cylindrical pattern was estimated over Sacramento, California. To better constrain the emission fluxes, we designed flights in a cylindrical pattern and computed the emission fluxes from two flights using a kriging method and Gauss’s divergence theorem. Differences in wind treatment and assumptions about background concentrations affect the emission estimates by a factor of 1.5 to 7. The uncertainty is also impacted by meteorological conditions and distance from the emission sources. The total flux estimates accounting for the entire circumference are larger than those based solely on measurements made in the downwind region. This indicates that a closed-shape flight profile can better contain total emissions relative to a one-sided curtain flight because most cities have more than a point source and wind direction can change with time and altitude. To reduce the uncertainty of the emission estimate, it is important that the sampling strategy account not only for known source locations but also possible unidentified sources around the city. Other than CO2 and CH4 emission estimates study, the recent studies regarding long-range ozone transport and extreme precipitation events (e.g. atmospheric rivers) are also briefly introduced.