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| Diffusion rates of organic molecules in secondary organic aerosol particles at low temperatures: measurements, predictions and implications | |
| 项目编号 | P2EZP2_191837 |
| Mahrt Fabian | |
| 项目主持机构 | Institution abroad - IACH |
| 开始日期 | 2020-02-01 |
| 结束日期 | 2021-07-31 |
| 英文摘要 | Secondary organic aerosol (SOA) is an important type of tropospheric particulate matter. SOA is mainly formed through oxidation of gaseous volatile organic compounds (VOCs), emitted from both biogenic and anthropogenic sources. SOA particles play an important role in atmospheric chemistry and air quality by providing a medium for heterogeneous chemical reactions and by transporting pollutants over large distances. SOA particles also play a key role in regulating climate. Despite the importance of SOA particles, our understanding of their physicochemical properties remains limited. One property that is insufficiently understood are the diffusion rates of organic molecules within SOA particles, especially at temperatures < 290 K. This temperature range covers most of the conditions in the troposphere, the region of the atmosphere most relevant for climate and air quality. This poor understanding of organic molecular diffusion rates leads to major uncertainties when estimating the environmental impacts of SOA. For instance, diffusion rates influence the SOA particle growth and evaporation rates, i.e. particle mass and size distributions. These in turn determine the way particles absorb and scatter radiation, i.e. their direct climate effect. The initial goal of this project is to directly measure diffusion rates of organic molecules in SOA particles as a function of temperature (T), specifically focusing on T < 290 K. Diffusion rates will be measured in SOA using the technique of rec-tangular area fluorescence recovery after photobleaching (rFRAP). These experiments will be carried out as a function of both temperature and water activity (aw; aw = relative humidity/100 at thermodynamic equilibrium). Since water is a plasticizer, diffusion rates will depend on aw in addition to temperature. To accomplish this goal, a novel flow cell with in-situ temperature and water activity control that can be directly coupled to a scanning confocal microscope for the rFRAP measurements will be designed and developed. After successful implementation of the novel flow cell, diffusion rates of organics in both biogenic SOA and anthropogenic SOA will be measured. Biogenic SOA will be generated by the oxidation of biogenic VOCs such as a-pinene, and anthropogenic SOA will be generated by the oxidation of anthropo-genic VOCs such as toluene.In addition to quantifying diffusion rates as a function of temperature and aw, in collaboration with external partners, we will also measure the chemical composition of the SOA using high-resolution mass spectrometry. Using the measured diffusion rates and measured chemical composition, we will test parametrizations currently used in atmospheric models to estimate diffusion rates of organic molecules in SOA. Finally, using the measured diffusion rates, we will determine if organic molecules are well mixed within SOA in the troposphere on the order of 1 hour, an assumption often used in atmospheric models when predicting air quality and climate. To accomplish this goal, we will use the meteorological fields (T, aw) obtained from the chemistry transport model of the Goddard Earth Observing System Model, Version 5 (GEOS-5), together with the measured diffusion rates to calculate mixing times of organic molecules in SOA particles in the troposphere, as a function of latitude, longitude and altitude. If organic molecules are not well mixed within SOA in the troposphere on the order of 1 hour, many of the previous predictions of air quality and climate involving SOA may not be accurate. Overall, the results from this project will lead to improved future projections of air quality and climate. |
| 学科分类 | 0805 - 大气科学;08 - 地球科学 |
| 资助机构 | CH-SNSF |
| 项目类型 | Careers;Fellowships |
| 国家 | CH |
| 语种 | 英语 |
| 文献类型 | 项目 |
| 条目标识符 | http://gcip.llas.ac.cn/handle/2XKMVOVA/191301 |
| 推荐引用方式 GB/T 7714 | Mahrt Fabian.Diffusion rates of organic molecules in secondary organic aerosol particles at low temperatures: measurements, predictions and implications.2020. |
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