GAQC | 不同环境中羟基自由基的来源、去除以及未知化学

GAQC简介

Global Air Quality Conversation (GAQC)是在教育部“高等学校学科创新引智计划”的资助下，由北京大学环境科学与工程学院主办的国际系列研讨会，主要包括四个主题：大气污染形成化学机制、大气监测与模拟、空气质量与气候变化以及大气污染的健康效应，针对每一主题邀请国际有影响力的专家做主题报告并就最新研究成果进行小规模讨论。项目旨在交流国际前沿研究成果、增强国际学术合作并为学生开拓国际视野和开发科研新思路。

会议信息

时间

11月25日（周五）晚  19:00-20:30

平台

Zoom在线会议平台

会议

安排

19:00 - 20:00   主题汇报 + 提问

20:00 - 20:15   BBP Q&A

20:15 - 20:30   指定论文学术讨论

嘉宾介绍

Lisa Whalley is a Senior Research Fellow

Senior Research Fellow in the School of Chemistry at University of Leeds. Her research interest lies in understanding the chemistry responsible for the processing of trace gases in the atmosphere through field observation and comparison of these observations with detailed chemistry models based on the Master Chemical Mechanism (MCM). Using laser induced fluorescence (LIF) her group has made measurements of OH on over 20 field projects in a variety of environments including Polar, Urban, Rural and Tropical regions with the aim of identifying the important chemical processing occurring in these key global areas. Alongside OH measurements, her group have developed methodologies to use LIF for detection of other radical species, such as iodine monoxide, IO, and organic peroxy radicals, RO2.

讲座内容

    1）主题讲座（20:00-21:00）： 

Understanding hydroxyl radical processing of trace gases in a variety of environments

The hydroxyl radical (OH) mediates virtually all of the oxidative chemistry in the atmosphere. Global OH concentrations control the lifetime of the climate gas, methane. Whilst in urban regions OH-initiated reactions dominate the transformation of primary emissions into secondary pollutants such as NO₂, O₃ and secondary organic aerosols. Combining measurements of OH, peroxy radicals and OH reactivity with near-explicit chemistry models and budget analyses can provide a means to test our understanding of the chemistry occurring in a particular environment.

Taking examples of field observations and model comparisons of radical concentrations in a variety of environments ranging from the pristine open ocean to polluted mega-cities, this talk will demonstrate atmospheric conditions where the chemistry is understood and environments where our understanding of the chemistry is incomplete and highlight that understanding the sources and sinks of OH in the atmosphere is essential in improving predictions of the lifetime of trace gases.

      2）面对面访谈（21:00-21:15）：

    由我院BBP卓越环境国际班的本科生代表与Porf.  Lisa Whalley进行交流。相关回答和感悟，定期将发表在BBP·交流栏目中。欢迎关注BBP卓越环境国际班公众号了解更多信息~    

 3）小组讨论（21:15-21:30）：

Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NOx in Beijing

Measurements of OH, HO₂, complex RO₂ (alkene- and aromatic-related RO₂) and total RO₂ radicals taken during the integrated Study of AIR Pollution PROcesses in Beijing (AIRPRO) campaign in central Beijing in the summer of 2017, alongside observations of OH reactivity, are presented. The concentrations of radicals were elevated, with OH reaching up to 2.8 × 10⁷ molecule cm⁻³, HO₂ peaking at 1 × 10⁹ molecule cm⁻³ and the total RO₂ concentration reaching 5.5×10⁹ molecule cm⁻³. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbv h⁻¹) under the very low NO conditions (< 0.5 ppbv) experienced in the afternoons, demonstrating a missing OH source consistent with previous studies under high volatile organic compound (VOC) emissions and low NO loadings. Under the highest NO mixing ratios (10⁴ ppbv), the HO₂ production rate exceeded the rate of destruction by ≈ 50 ppbv h⁻¹, whilst the rate of destruction of total RO₂ exceeded the production by the same rate, indicating that the net propagation rate of RO₂ to HO₂ may be substantially slower than assumed. If just 10 % of the RO₂ radicals propagate to HO₂ upon reaction with NO, the HO₂ and RO₂ budgets could be closed at high NO, but at low NO this lower RO₂ to HO₂ propagation rate revealed a missing RO₂ sink that was similar in magnitude to the missing OH source. A detailed box model that incorporated the latest Master Chemical Mechanism (MCM3.3.1) reproduced the observed OH concentrations well but over-predicted the observed HO₂ under low concentrations of NO (< 1 ppbv) and under-predicted RO₂ (both the complex RO₂ fraction and other RO₂ types which we classify as simple RO₂) most significantly at the highest NO concentrations. The model also under-predicted the observed k(OH) consistently by ≈ 10 s⁻¹ across all NOx levels, highlighting that the good agreement for OH was fortuitous due to a cancellation of missing OH source and sink terms in its budget. Including heterogeneous loss of HO₂ to aerosol surfaces did reduce the modelled HO₂ concentrations in line with the observations but only at NO mixing ratios < 0.3 ppbv. The inclusion of Cl atoms, formed from the photolysis of nitryl chloride, enhanced the modelled RO₂ concentration on several mornings when the Cl atom concentration was calculated to exceed 1 × 10⁴ atoms cm⁻³ and could reconcile the modelled and measured RO₂ concentrations at these times. However, on other mornings, when the Cl atom concentration was lower, large under-predictions in total RO₂ remained. This demonstrates the rate at which the larger RO₂ species propagate to HO₂, to another RO₂ or indeed to OH needs to be understood to accurately simulate the rate of ozone production in environments such as Beijing, where large multifunctional VOCs are likely present.

文章链接：                  

https://acp.copernicus.org/articles/21/2125/2021/

文章二维码：

报名方式

请有意向参会的各位老师同学打开链接或扫描下方二维码，期待您的参与！

https://us06web.zoom.us/j/88954837218?pwd=aUk4Z2RMcEMzNEtsTHliNlgweUJ3UT09

未来讲座

12.09：GAQC | Ronald C. Cohen

往期回顾

03.11：GAQC | Neil M. Donahue

What makes particles grow in Beijing?

03.25：GAQC | Frank Keutsch

Role of Organic Hydroperoxides and Formaldehyde Catalysis in Particulate Matter Formation 

04.09：GAQC | Joost de Gouw

Emissions from Wildfires, Oil and Gas Production and the Effects of COVID-19 

04.22：GAQC | Frank Kelly

Toxicity of Airborne Particles: Established Evidence and Knowledge Gaps 

05.13：GAQC | Hendrik Fuchs 

Photochemically produced air pollution in China: Insights from field campaigns  

05.27：GAQC | Oliver Wild

Using air quality models to inform short-term emission controls  

09.23：GAQC | Eloise Marais

Deleterious effects of space sector air pollutant emissions on climate and stratospheric ozone 

10.14：GAQC | Audrey Gaskins

Air Pollution, Climate Change, and Human Reproduction 

10.28：GAQC | Junfeng Zhang

Ozone versus Ozone Reaction Products:

Which Is More Responsible for Cardiorespiratory Effects? 

11.11：GAQC | Róisín Commane

Carbon dioxide and methane in Arctic and urban atmospheres

组织者 | 刘妍慧，Theodore Koenig

往期精选