Atmospheric photochemistry and secondary aerosol formation of urban air in Lyon,France

Photochemical aging of volatile organic compounds(VOCs)in the atmosphere is an important source of secondary organic aerosol(SOA).To evaluate the formation potential of SOA at an urban site in Lyon(France),an outdoor experiment using a Potential Aerosol Mass(PAM)oxidation flow reactor(OFR)was conducted throughout entire days during JanuaryFebruary 2017.Diurnal variation of SOA formations and their correlation with OH radical exposure(OHexp),ambient pollutants(VOCs and particulate matters,PM),Relative Humidity(RH),and temperature were explored in this study.Ambient urban air was exposed to high concentration of OH radicals with OHexp in range of(0.2-1.2)×10^12 molecule/(cm^3·sec),corresponding to several days to weeks of equivalent atmospheric photochemical aging.The results informed that urban air at Lyon has high potency to contribute to SOA,and these SOA productions were favored from OH radical photochemical oxidation rather than via ozonolysis.Maximum SOA formation(36μg/m^3)was obtained at OHexp of about 7.4×10^11 molecule/(cm^3·sec),equivalent to approximately 5 days of atmospheric oxidation.The correlation between SOA formation and ambient environment conditions(RH&temperature,VOCs and PM)was observed.It was the first time to estimate SOA formation potential from ambient air over a long period in urban environment of Lyon.

Measurement of heterogeneous uptake of NO2 on inorganic particles, sea water and urban grime

Heterogeneous reactions of NO2 on different surfaces play an important role in atmospheric NOxremoval and HONO formation,having profound impacts on photochemistry in polluted urban areas.Previous studies have suggested that the NO2 uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime.However,the uptake behavior of NO2 varies with different surfaces,and different uptake coefficients were used or derived in different studies.To obtain a more holistic picture of heterogeneous NO2 uptake on different surfaces,a series of laboratory experiments using different flow tube reactors was conducted,and the NO2 uptake coefficients(γ)were determined on inorganic particles,sea water and urban grime.The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions,with the measuredγvaried from<10-8 to 3.2×10-7 under different humidity.A photo-enhanced uptake of NO2 on urban grime was observed,with the obvious formation of HONO and NO from the heterogeneous reaction.The photo-enhancedγwas measured to be 1.9×10-6 at 5%relative humidity(RH)and 5.8×10-6 at 70%RH on urban grime,showing a positive RH dependence for both NO2 uptake and HONO formation.The results demonstrate an important role of urban grime in the daytime NO2-to-HONO conversion,and could be helpful to explain the unknown daytime HONO source in the polluted urban area.

Preface

Air pollution as well as climate change and their possible effects on the environment, ecosystems and human health, are pressing challenges. Nowadays, it is dear that sustainable societal development cannot remain solely wealth-oriented, but must take into account the present and future environmental issues. However, this approach is possible only if scientifically sound knowledge in all environmental areas becomes available to our societies and decision makers, which requires a firm scientific basis to our understanding of the processes guiding the atmospheric compositions.

在腐植酸上二氧化氮光敏还原制备亚硝酸

研究结果表明,土壤和其他含有腐植酸的表面,具有一种能产生还原表面物质的有机表面光化学,而这种还原表面物质可以选择性地与二氧化氮反应。亚硝酸形成的表观速率可以解释最近观察到的白天在边界层中亚硝酸高浓度现象,亚硝酸的光分解占整个羟基自由基源的60%。我们认为这种在腐植酸上的光诱导亚硝酸产物对最低对流层的化学过程有潜在的重要影响。

Impact of photocatalytic remediation of pollutants on urban air quality

In the recent years, photocatalytic self-cleaning and ＂depolluting＂ materials have been suggested as a remediation technology mainly for NOx and aromatic VOCs in urban areas. A number of products incorporating the aforementioned technology have been made commercially available with the aim to improve urban air quality. These commercial products are based on the photocatalytic properties of a thin layer of TiO2 at the surface of the material （such as glass, pavement, etc.） or embedded in paints or concrete. The use of TiO2 photocatalysts as an emerging air pollution control technology has been reported in many locations worldwide. However, up to now, the effectiveness measured in situ and theexpected positive impact on air quality of this relatively new technology has only been demonstrated in a limited manner. Assessing and demonstrating the effectiveness of these depolluting techniques in real scale applications aims to create a real added value, in terms of policy making （i.e., implementing air quality strategies） and economics （by providing a demonstration of the actual performance of a new technique）.

Preface

One of the most important challenges the world is facing in this century is how to achieve sustained global development while balancing economic, societal and environmental considerations. It is clear that providing everyone a healthy and wealthy society can only be achieved if upcoming policies and initiatives from policy makers are based on the most up-todate and validated scientific knowledge.