Concentrations and stable carbon isotope compositions of oxalic acid and related SOA in Beijing before, during, and after the 2014 APEC

Abstract. To ensure good air quality for the 2014 Asia-Pacific Economic Cooperation (APEC) summit, stringent emission controls were implemented in Beijing and its surrounding regions, leading to a significant reduction in PM2.5 loadings. To investigate the impact of the emission controls on aerosol chemistry, high-volume PM2.5 samples were collected in Beijing from 8 October to 24 November 2014 and determined for secondary inorganic aerosols (SIA, i.e., SO42−, NO3−, and NH4+), dicarboxylic acids, keto-carboxylic acid, and α-dicarbonyls, as well as stable carbon isotope composition of oxalic acid (C2). Our results showed that SIA, C2, and related secondary organic aerosols in PM2.5 during APEC were 2–4 times lower than those before APEC, which is firstly ascribed to the strict emission control measures and secondly attributed to the relatively colder and drier conditions during the event that are unfavorable for secondary aerosol production.C2 in the polluted air masses, which mostly occurred before APEC, are abundant and enriched in 13C. On the contrary, C2 in the clean air masses, which mostly occurred during APEC, is much less abundant but still enriched in 13C. In the mixed type of clean and polluted air masses, which mostly occurred after APEC, C2 is lower than that before APEC but higher than that during APEC and enriched in lighter 12C. A comparison on chemical composition of fine particles and δ13C values of C2 in two events that are characterized by high loadings of PM2.5 further showed that after APEC SIA and the total detected organic compounds (TDOC) are much less abundant and fine aerosols are enriched with primary organics and relatively fresh, compared with those before APEC.

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Molecular distributions and stable carbon isotope compositions of oxalic acid and related SOA in Beijing before, during and after the 2014 APEC

10.5194/acp-2016-662 ◽

2016 ◽

Author(s):

Jiayuan Wang ◽

Gehui Wang ◽

Jian Gao ◽

Han Wang ◽

Yanqin Ren ◽

...

Keyword(s):

Oxalic Acid ◽

Carbon Isotope ◽

Isotope Composition ◽

Stable Carbon Isotope ◽

Dicarboxylic Acids ◽

Photochemical Oxidation ◽

Stable Carbon ◽

Aerosol Composition ◽

Air Masses ◽

Emission Controls

Abstract. To ensure the good air quality for the 2014 APEC, stringent emission controls were implemented in Beijing and its surrounding regions, leading to a significant reduction in PM2.5 loadings. To investigate the impacts of the emission controls on aerosol composition and formation, high-volume PM2.5 samples were collected in Beijing from 08/10/2014 to 24/11/2014 and determined for secondary inorganic ions (SIA, i.e., SO42−, NO3− and NH4+), dicarboxylic acids, keto-carboxylic acid and α-dicarbonyls, as well as stable carbon isotope composition of oxalic acid (C2). Our results showed that SIA in PM2.5 are 52 ± 47, 18 ± 13 and 33 ± 29 μg m−3 before-, during- and after-APEC, accounting for 29 %, 18 % and 20 % of PM2.5, respectively. As the leading dicarboxylic acid, C2 in PM2.5 during the three phases are 502 ± 564, 101 ± 69 and 166 ± 157 ng m−3, accounting for 46 %, 31 % and 34 % of total detected organic compounds (TDOC, i.e., the sum of dicarboxylic acids, keto-carboxylic acids and α-dicarbonyls). The higher values of concentrations and relative abundances of SIA and C2 before-APEC suggest that PM2.5 aerosols during this period are more enriched with secondary products, mainly due to an enhanced photochemical oxidation under the higher temperature and more humid conditions. SIA, C2 and related SOA in PM2.5 during-APEC were 2–4 times lower than those before-APEC. C2 in the regional air masses, which mostly occurred before-APEC, are abundant and enriched in 13C. On the contrary, C2 in the long-range transport air masses, which mostly occurred during-APEC, is much less abundant but still enriched in 13C. In the local air masses, which mostly occurred after-APEC, C2 concentration is lower than that before-APEC but higher than that during-APEC and enriched in lighter 12C. A comparison on chemical composition of PM2.5 and δ13C values of C2 in two events that are characterized by the highest PM2.5 levels before- and after-APEC, respectively, further showed that after-APEC SIA and TDOC are much less abundant and fine aerosols are enriched with primary organics and relatively fresh, compared with those before-APEC. Such reduction in secondary aerosols after-APEC, along with a similar reduction during-APEC, is largely due to the decreasing temperatures. Our results indicate that the significant reduction in PM2.5 during-APEC is mainly due to the efficient emission controls, but the effect of the decreasing temperatures, which suppressed secondary aerosol production, may also take an important role.

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Stable Carbon Isotope Ratios in Atmospheric VOC during the EMeRGe-EU and ASIA campaigns

10.5194/egusphere-egu2020-7597 ◽

2020 ◽

Author(s):

Marc Krebsbach ◽

Ralf Koppmann

Keyword(s):

Carbon Isotope ◽

Critical Role ◽

Stable Carbon Isotope ◽

Isotope Ratios ◽

Stable Carbon ◽

Air Masses ◽

Air Samples ◽

Stable Carbon Isotope Ratios ◽

Carbon Isotope Ratios ◽

The Impact

VOC (volatile organic compounds) play a critical role in the chemistry of the atmosphere. The formation of many important secondary pollutants in the atmosphere, such as ozone, peroxides, aldehydes, and peroxyacyl nitrates and secondary organic particulate matter depends critically on the availability of VOC as their precursors. Many of them have strong direct adverse effects on our environment. The assessment of the impact of VOC on the atmosphere can be significantly improved by measuring their stable carbon isotope ratios. The isotopic composition of compounds emitted by natural or anthropogenic activities vary for emissions from different sources. In almost all atmospheric processes, e.g. chemical reactions, photolytic processes, transport and dilution, diffusion, and phase transitions, the isotopic ratio in VOC is altered. Studying the isotope ratios of both precursors and products makes it possible to distinguish between freshly emitted VOC and photochemically processed compounds, to increase our knowledge of transport versus chemistry, to study the ultimate fate of oxidation products, and to help assess the impact of emissions, e.g. from large population centres (MPCs), on local, regional and even global pollution. The automated high volume air sampling system MIRAH has been deployed during several missions with the German High Altitude &#8211; Long-range research aircraft (HALO). Here we focus on the campaigns EMeRGe-EU and -ASIA (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales). The objectives were to measure the pollution emitted, transported and transformed from the MPCs London, BeNeLux, Rhine-Ruhr and Po Valley for the European Part. The second part of EMeRGe was conducted from Taiwan with the goal to investigate the pollution outflow from Asian MPCs such as Taipei, Hongkong, Shanghai, Beijing, Manila, Seoul and Tokio. In both parts a key experiment was the identification of the source of the air masses by collecting whole air samples on ground prior and during particular flights in specific metropolitan regions. On 7 flights in Europe and 12 flights in Asia, mostly below 6 km altitude, more than 140 air samples were collected on HALO during each campaign, and additional 46 samples at specific ground sides. The whole air samples were analysed for mixing ratios and stable carbon isotope ratios of selected aldehydes, ketones, alcohols, and aromatics. This allowed investigating air masses of different origin, characteristic, and atmospheric processing. In this presentation we will give an overview of the data and show exemplary results. This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG Priority Program SPP 1294) under grant-No. KR3861/1-1.

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