Project No: 16302220

Title: Impact of brown carbon on meteorological factors and ozone concentration

Principal Investigator: Prof. Jimmy Chi Hung FUNG

Co-Investigator: Prof. Yuhang WANG

Abstract:

As one of the most important ambient pollutants, aerosols can exert adverse effects on air quality, visibility, and human health. From the aspect of climate, aerosols can absorb, scatter, or reflect sunlight depending on their composition and color. In general, nonlight absorbing aerosols (e.g., sulfate and nitrate) tend to reflect solar radiation into space, whereas dark-colored aerosols (e.g., black carbon) absorb large amounts of light. These two types of aerosols have opposite climatic effects; that is, the reflection of solar radiation can cool the atmosphere, whereas the absorption of light can warm the atmosphere. Most organic aerosols (OAs) are classified as light-colored aerosols and considered as purely scattering in most climate models. However, OAs contain large amounts of brown carbon (BrC), which has a strong light absorption capability instead of merely scattering light. BrC is mainly contributed by incomplete combustion processes, such as open biomass burning and residential biofuel use. The quantification of the BrC effect by using a numerical model remains uncertain because of the great variability of optical properties and BrC sources. When BrC is exposed to sunlight, photobleaching effect can degrade its light absorption capability. Few modeling studies have considered this effect in their simulations. To better quantify the effect of BrC heated by the absorbed solar radiation on regional pollutant distributions, we propose to parameterize BrC into a Weather Research Forecast (WRF)-Community Multiscale Air Quality Modeling System (CMAQ), which is a two-way coupled model based on recent experimental studies. A novel BrC basis set (BCBS) framework is also proposed in this work. This framework considers how the light absorption property of BrC varies with the emission condition (BC/OA ratio) and the length of sunlight exposure. Southern China is heavily influenced by biomass burning, and no regional BrC simulation has been performed in this region. Hence, a whole-year simulation (12 km resolution) will be carried out with the BCBS framework to carefully investigate the effects of BrC on O3 concentration, radical budget, solar radiation and other meteorological variables (e.g., temperature and precipitation) in different months. From the perspective of BrC, the impacts of recent 20-year variations in biomass burning on meteorological factors, ozone concentration, and HOx budget will also be investigated. Upon completion of the project, the impacts of BrC on climate and air quality will be thoroughly understood.