学术报告:Global Modeling of Carbonaceous Aerosols and Wildfires
报告题目:Global Modeling of Carbonaceous Aerosols and Wildfires
报 告 人: Yaoxian Huang
单 位: School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511
Carbonaceous aerosols that include organic carbon and black carbon, have significant implications for both climate and air quality. In the current global climate or chemical transport models, a simplified hydrophobic to hydrophilic conversion lifetime for carbonaceous aerosol (t) is generally assumed, which is usually around 1 day. A new physical condensation-coagulation and chemical oxidation aging scheme for carbonaceous aerosols has been implemented in GEOS-Chem. Atmospheric parameters, including water vapor, ozone, hydroxyl radicals and sulfuric acid concentrations, affect the hydrophobic-to-hydrophilic conversion lifetime (τ) for carbonaceous aerosols. The updated τ shows large spatial and temporal variations with the global average calculated to be about 2.6 days (up to 11 km altitude). Compared to the control simulation, the updated aging scheme increases the global burdens of BC (OC) by 9% (3%). Considerable enhancements of carbonaceous aerosols are observed in the Southern Hemisphere. Additionally, the updated aging scheme improves model simulations of carbonaceous aerosols for the remote areas in the Northern Hemisphere revealed from the comparisons to multiple observational datasets.
The occurrence of wildfires is very sensitive to fire meteorology, vegetation type and coverage. We investigate the potential impacts of global change (including changes in climate, land use/land cover, and population density) on wildfire frequencies over the period of 2000-2050. We account for the impacts associated with the changes in fire meteorology (such as temperature, precipitation, and relative humidity), vegetation density, as well as lightning and anthropogenic ignitions. Fire frequencies under the 2050 conditions are projected to increase by approximately 27% globally relative to the 2000 levels. Changes in fire meteorology driven by 2000-2050 climate change are found to increase the global annual total fires by around 19%. Modest increases (~ 4%) in fire frequency at tropical regions are calculated in response to climate-driven changes in lightning activities, relative to the present-day levels. Changes in land cover by 2050 driven by climate change and increasing CO2 fertilization are expected to increase the global wildfire occurrences by 15% relative to the 2000 conditions while the 2000-2050 anthropogenic land use changes show little effects on global wildfire frequency. The 2000-2050 changes in global population are projected to reduce the total wildfires by about 7%.