G01_P01

Changes in fossil CO₂ emissions in Mexico City during the Covid-19 lockdown deduced from atmospheric radiocarbon concentrations

Beramendi-Orosco L^1,3, González-Hernández G^2,3, Cienfuegos E^1,3, Otero F^1,3, Santos-Arévalo F⁴, Gómez-Martínez I⁴

¹Instituto de Geología, UNAM, Ciudad De México, Mexico, ²Instituto de Geofísica, UNAM, Ciudad de México, Mexico, ³Laboratorio Nacional de Geoquímica y Mineralogía, UNAM, Ciudad de México, Mexico, ⁴Centro Nacional de Aceleradores, Sevilla, Spain

The Mexico City Metropolitan Area is a complex megacity with a mixture of CO₂ emission sources, where atmospheric ¹⁴C variability is influenced mainly by changes in fossil fuels burning and wildfires in the mountains surrounding the valley, common during the hot-dry spring season. In this contribution we present atmospheric radiocarbon concentrations from CO₂ monthly-integrated samples taken between January 2019 – June 2021 at the southern area of the Mexico City Basin and explain the changes in terms of the Covid-19 lockdown and restrictions imposed form March 2020. To stop the spread of the Covid-19 epidemy, the Mexican government imposed a partial lockdown closing schools and universities on 20th of March 2020, extending the lockdown to all non-essential activities with a significant reduction in public transport services on 30th of March, and further restrictions with a complete lockdown imposed on 21st of April when the country started the phase of higher risk of Covid-19 transmission. This complete lockdown lasted up to 13th of May, and from 1st of July some non-essential activities were gradually opened with some restrictions in place up to 2021, and schools and universities remaining closed up to September 2021. Atmospheric radiocarbon concentrations clearly followed the different phases of the Covid-19 restrictions, with significantly higher values (p<0.001) during March – May 2020, indicating, as expected, an important reduction of fossil CO₂ emissions. Furthermore, the post-March 2020 values are higher with lower variability, ranging between 0.9906–1.0108, as compared to the pre-Covid-19 pandemic values, ranging between 0.9639–0.9951.

G01_P02

Evolution of fossil and non-fossil emission sources of carbonaceous aerosol in the Swiss Plateau from 2012 to 2020

Crova F^1,2, Strähl J², Szidat S²

¹Department of Physics, Università degli Studi di Milano, and INFN-Milano, Milan, Italy, ²Department of Chemistry, Biochemistry and Pharmaceutical Sciences, and Oeschger Centre for Climate Change Research, Bern, Switzerland

Carbonaceous aerosols are a major component of the fine fraction of atmospheric aerosol; moreover, they can influence Earth’s climate and are related to adverse health effects. Therefore, the identification and quantification of their emission sources are crucial.

In Switzerland, like in many other European countries, control strategies for ambient air pollution have focused mostly on emissions deriving from fossil fuel combustion (e.g., road traffic), but non-fossil contributions can be the predominant sources of carbonaceous aerosols in different periods of the year (e.g., biomass burning during winter) [Zotter et al., 2014]. Consequently, studying the evolution over long periods of the relative contributions of fossil and non-fossil sources of carbon is mandatory to understand the variation of their impact.

In this work, a source apportionment study of carbonaceous aerosol sources in the Swiss Plateau region from 2012 to 2020 was carried out by performing radiocarbon measurements on separated carbon fractions. Indeed, such measurements have been proved to be very effective to separate the contribution of different carbon emission sources in the atmosphere [Szidat et al., 2006]. Aerosol samples in the size fraction PM2.5 collected daily by Empa (Swiss Federal Laboratories for Material Science and Technology) in three different monitoring stations (Bern, Zurich, and Payerne) were exploited for this purpose. Radiocarbon measurements were performed by accelerator mass spectrometry (AMS) at the Laboratory for the Analysis of Radiocarbon with AMS (LARA) at the University of Bern on the total and elemental carbon fractions. Preliminary results concerning the site of Bern will be presented.

G01_P03

Radiocarbon concentration of wheat (Triticum aestivum L.) and soybean seeds (Glycine max (L.) Merr.) grown during the bomb spike.

Huels M¹, Hamann C¹, Börner A²

¹Christian-albrechts-university, Kiel, Germany, Kiel, Germany, ²2) Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Seeland, OT Gatersleben, Germany

Here we report radiocarbon measurements made on soybean seeds (Glycine max (L.) Merr.), grown and harvested on the experimental fields of the IPK in Gatersleben, Saxony-Anhalt, Germany, between 2000-2021, complementing the ¹⁴C measurements from wheat seeds over the bomb-spike (Hüls et al 2021).

Soy is sown around mid May and harvested by the end of September / beginning of October, forming its main bean tissue between July and October. The results give an overview of ¹⁴C in agricultural grown plant tissue during the growth-period between April to September. The combined wheat and soybean seed radiocarbon record is compared to known pre- and post-bomb radiocarbon records (e.g. atmospheric Jungfraujoch, Schauinsland, and NH₁ datasets).

The Gatersleben plant tissue radiocarbon concentration indicates incorporation of fossil carbon of about 1% with respect to the high alpine, clean-air CO₂ of the Jungfraujoch station between 1987 and 2019. As shown previously with wheat seed (Hüls et al 2021), recent (i.e. 2021) grown plant-tissue give apparent ¹⁴C concentrations slightly below the 1950 reference level (i.e., -5.3±2 ‰ for wheat, -6.9±3‰ for soybean, respectively).

We suggest to use the pre- and post-bomb radiocarbon record of Gatersleben seeds as a reference in forensic investigations, such as the age estimation of paper by analyzing starch used in paper manufacture. A further advantage of the dataset reported here lies in its comparably simple extensibility by adding new analyses from future harvests.

G01_P04

Vertical dynamics of particulate carbon sources during a haze pollution episode using the measurements of dual-carbon isotopes

Jiang F^1,2, Liu J¹, Strähl J², Szidat S², Wang Y¹, Cheng Z^3,7, Zhu S^3,7, Ding P^4,7, Cao F⁵, Zhang Y⁵, Zhou S⁶, Zheng J¹, Li J^3,7, Zhang G^3,7

¹Institute for Environmental and Climate Research, Jinan University, Guangzhou, China, ²Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ³State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, ⁴State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, ⁵Yale-NUIST Center on Atmospheric Environment, International Joint Laboratory on Climate and Environment Change, Nanjing University of Information Science and Technology, Nanjing, China, ⁶School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China, ⁷CAS Center for Excellence in Deep Earth Science, Guangzhou, China

Carbonaceous aerosols, an important component of PM₂.₅, have been identified as the critical trigger influencing the formation and evolution of severe atmospheric haze pollution in many regions around the world. Stable carbon isotope (¹³C) and radiocarbon (¹⁴C) measurements are powerful tools for identifying and quantifying the relative contributions of key sources to haze pollution. In this study, we investigated the dynamic changes of the signals of ¹³C and ¹⁴C in PM₂.₅ samples collected at different heights of the Canton Tower in Guangzhou in South China in the 2020/2021 winter season, during which a severe haze episode occurred. The ¹⁴C measurements showed that there is an obvious difference in the sources of total carbon aerosol among different heights. In addition, we found that the ¹⁴C signals varied dramatically during this haze episode, suggesting that the sources of particulate carbon were constantly changing during the formation and evolution of the atmospheric haze pollution. To further investigate the sources and formation mechanisms of this haze event, we will 1) refine the source information based on the measurements of ¹³C and ¹⁴C in subfractions of total carbon; 2) find out the key source and mechanism that triggered this haze pollution.

G01_P05

Source apportionment of atmospheric and sedimentary PAHs from Kolkata, India by using compound-class-specific radiocarbon analysis (CCSRA)

Kumata H¹, Uchida M², SAHA M^3,4, Mantoku K², Kobayashi T², Okuda T⁵, Shibata Y^2,6, Takada H³

¹Tokyo University of Pharmacy and Life Sciences, Hachioji, Japan, ²National Institute for Environmental Studies, Tsukuba, Japan, ³Tokyo University of Agriculture and Technology, Fuchu, Japan, ⁴Now at National Institute for Oceanography , , India, ⁵Keio University, Yokohama, Japan, ⁶Tokyo University of Science, Tokyo, Japan

Asia is one of the most important source regions for short-lived climate pollutant (SLCP), to the atmosphere. For polycyclic aromatic hydrocarbons (PAHs), known as major mutagens in atmospheric aerosols, Asian megacities have the highest levels across the globe.

We conducted compound-class-specific radiocarbon analyses (CCSRA) for surface sediments and aerosols collected in city center of Kolkata. Surface sediments were collected from city canals using a grab sampler. The study site was chosen because the preliminary survey showed it has extremely high-level contamination. Collected sediments were roughly sectioned on-site and approximately upper half (0-7 cm, depth from the surface of the sediment) was used. The ƒC values of sedimentary PAHs in Kolkata city canal sediments ranged 0.056 to 1.0 in the north canal and 0.078 to 0.080 in the south canal, indicating strong influences (i.e., >90%) from fossil fuel combustions. Combined with molecular fingerprinting study, relative contribution from coal combustion in brickyards to sedimentary PAHs was estimated to be >50%. As monsoon driven runoff events flush canals every year, this may portray the input of particle-borne pollution over the last few years. Based on the results obtained, we discuss the importance of contemporary sources of combustion-derived PAHs in Indian Mega city.

G01_P06

Characterization of Carbonaceous Components and Fossil and Non-Fossil Carbon Contents in Fine Aerosols in the Eastern Mediterranean Troposphere

Pavuluri C^1,2, Mihalopoulos N³, Uchida M⁴, Mantoku K⁴, Fu P^1,2, Kawamura K^1,5

¹Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan, ²Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin, China, ³ECPL, Department of Chemistry, University of Crete, Heraklion, Greece, ⁴AMS Facility (NIES-TERRA), National Institute for Environmental Studies, Tsukuba, Japan, ⁵Chubu Institute for Advanced Studies, Chubu University, Kasugai, Japan

Atmospheric fine (PM₁) aerosols are mainly produced by secondary processes and contain a major fraction of organic compounds, which have serious impacts on the Earth’s climate system directly by scattering and absorbing solar radiation and indirectly by acting as cloud condensation nuclei. They also cause adverse effects on human health and play an important role in atmospheric chemistry. It is well recognized that summertime ozone is enhanced in the Mediterranean troposphere and the aerosol radiative forcing is among the highest in the world over this region in summer. Although carbonaceous components have been studied well, their origins and atmospheric processing are not yet fully understood in the Mediterranean. We collected PM₁ samples at a remote marine background site, the Finokalia research station, in the Eastern Mediterranean troposphere on a weekly basis for two consecutive days each during a one-year period: October 2009 to October 2010. We measured the carbonaceous components: elemental carbon (EC) organic carbon (OC) and water-soluble OC (WSOC) and stable carbon (δ¹³C) and radiocarbon (Δ¹⁴C), a unique tracer for distinct fossil and non-fossil carbon, isotope ratios of total carbon (TC) in the PM1.0. Here we report (i) the characteristics of carbonaceous components and (ii) percent of modern carbon (pMC) in TC. Based on the results obtained together with their comparison with molecular marker species, we explore the origins and the extent of secondary formation of carbonaceous aerosols as well as their seasonality in the Eastern Mediterranean.

G01_P07

Abundance of Non-Fossil Carbon Content in the Tropical Indian Carbonaceous Aerosols

Pavuluri C^1,2, Uchida M³, Mantoku K³, Fu P^1,2, Kawamura K^1,4

¹Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan, ²Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin, China, ³AMS Facility (NIES-TERRA), National Institute for Environmental Studies, Tsukuba, Japan, ⁴Chubu Institute for Advanced Studies, Chubu University, Kasugai, Japan

Carbonaceous aerosols that represent a large fraction of fine aerosol mass have serious impacts on the Earth’s climate system directly by scattering and absorbing solar radiation and indirectly by acting as cloud condensation nuclei. They also cause adverse effects on human health and play an important role in atmospheric chemistry. Although carbonaceous components have been studied well, their origins and atmospheric processing are not yet fully understood in the tropical Indian aerosols. To apportion the fossil and contemporary carbon content in the tropical carbonaceous aerosols from the Indian region, we collected atmospheric aerosols (PM₁₀) on day- (approximately 6:00–18:00 LT) and nighttime (18:00–6:00 LT) bases in winter (January 23 to February 6, n = 29) and summer (May 22–31, n = 20) 2007 from a mega‐city, Chennai (13.04°N; 80.17°E) located on the southeast coast of India. We measured the carbonaceous components, molecular composition and distributions of various organic classes of compounds and their stable carbon isotopic composition (δ¹³C), and radiocarbon (Δ¹⁴C), a unique tracer for distinct fossil and non-fossil carbon, isotope ratios of total carbon (TC) in the PM₁₀. Here we report the characteristics of Δ¹⁴C as percent of modern carbon (pMC) in TC, together with the comparison with the carbonaceous components and molecular marker species in PM₁₀. Based on the results obtained, we discuss the importance of contemporary sources and aging of the tropical carbonaceous aerosols, including their diurnal and seasonal changes, in the Indian region.

G01_P08

Atmospheric CO₂ carbon isotope composition in urban and clean areas of costal Northern Croatia

Sironić A¹, Hess E², Borković D¹, Kanduč T³, Barešić J¹, Krajcar Bronić I¹

¹Ruđer Bošković Institute, Zagreb, Croatia, ²Department of Physics, University of Rijeka, Rijeka, Croatia, ³Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia

Fossil fuel combustion decrease ¹⁴C activity and ¹³C composition of atmospheric CO₂, which is also known as the Suess effect. For one year (2021), we have been monitoring carbon isotope composition of atmospheric CO₂ at locations under maritime influence of the Adriatic Sea: coastal city of Rijeka and at two clean air sites in vicinity, Gornje Jelenje and Parg with mountain climate.

Carbon isotope composition at all sites shows seasonal variation, with the lowest ¹⁴C activities and δ¹³C in winter-spring, and the highest in summer, ranging from -41.3 to 25.2 ‰ for Δ¹⁴C and -13.1 to -11.3 ‰ for δ¹³C, respectively. Rijeka has systematically the lowest and Parg the highest Δ¹⁴C, however δ¹³C at the sites are not statistically different one from another. Leaves of deciduous trees were also collected. Their Δ¹⁴C reflect the trend of atmospheric Δ¹⁴C, being the lowest at Rijeka and highest at Parg.

G01_P09

Variation of fossil CO₂ in Mexico City during the month of December before and after the COVID-19 partial lockdown.

Solis C¹

¹Universidad Nacional Autónoma de México, Mexico City, Mexico, ²Instituto Tecnológico de Estudios Superiores de Monterrey, CDMX, México, Mexico City, Mexico, ³Universidad Autónoma Metropolitana Azcapotzalco, Mexico City, Mexico

Mexico City (CDMX), the largest urban center in Mexico, has a population dynamics, industrial development, orography, and climate that make it a major source of pollution and health problems. Mexico City has 5.9 million vehicles and intense industrial activity. Fossil fuel consumption is responsible for 95% of CO₂ emissions. Due to the COVID 19 pandemic, the government imposed a partial shutdown of all non-essential activities since March 2020 in the public and private sector, schools and universities as part of containment measures. Vehicular traffic decreased by 62% relative to 2019. Because of the important decrease in vehicular traffic and other activities, CO₂ emissions decreased from 487,570 megatons in 2019 to 407,695 megatons in 2020. In this work, we applied the AMS detection of ¹⁴CO₂ to infer the reductions in the fossil fraction caused by the decrease in activities by COVID-19 pandemic. The ¹⁴CO₂ measurement was conducted in December (winter) 2020 and compared to the activity in the same month of 2019. The ¹⁴CO₂ measurement has been used to assess the emissions of the modern and fossil fractions.

Acknowledgements: Fís. Arcadio Huerta and Sergio Martínez for technical assistance. CONACYT 2022 grant.

G01_P10

Atmospheric radiocarbon analysis of grass samples; weekly resolution comparison and fossil fuel reconstruction of high traffic and background sites.

Usher E¹, Wood R², Esmay R¹, Fallon S¹

¹ANU Radiocarbon Dating Laboratory, Canberra, Australia, ²Oxford Radiocarbon Dating Laboratory , Oxford, UK

The atmosphere’s composition and dynamics, and particularly the role which carbon dioxide has within these, have become topics of increasing scientific importance in a world of anthropogenic climate change. The radioisotope composition of atmospheric CO₂ is an integral component for these topics as it can allow for anthropogenic influence to be identified and even quantified due to the Suess effect. Biotic assimilation proxies present an avenue to investigate atmospheric ¹⁴C at varying temporal and spatial scales. Grass as a biotic proxy has successfully been used to reconstruct fossil fuel contribution to atmospheric CO₂ in a point source analysis by Turnbull et al. (2016). In this work grass samples from three locations, two background and one sample site, will be analysed for F¹⁴C values in order to reconstruct the fossil fuel contribution (CO₂ff) from traffic next to one of Canberra’s busiest roads, Parkes Way Road. Grass is sampled weekly from these sites and cryogenically frozen until pre-treatment, then measured with an AMS. This work uses a relatively novel biotic proxy to identify emissions contributions from motor vehicles in Canberra. The early results from this study show that there is a measurable difference in F¹⁴C values between the background sites and the road site consistent with an average of ~4ppm contribution from CO₂ff.

Turnbull, J, Keller, E, Norris, M, Wiltshire, R. (2016). Independent evaluation of point source fossil fuel CO₂ emissions to better than 10%. Proceedings of the National Academy of Sciences. 113. 201602824. 10.1073/pnas.1602824113.

G01_P12

A sampling system for ¹⁴C analysis of atmospheric methane: from a laboratory prototype to an automated system.

Zazzeri G¹, Gautschi P¹, Graven H², Wacker L¹

¹ETH, Zürich, Switzerland, ²Imperial College London, London, United Kingdom

Measurements of radiocarbon (¹⁴C) in atmospheric methane (CH₄) provide a powerful tool to distinguish fossil from biogenic methane emissions, because fossil methane is completely devoid of ¹⁴C. However, these measurements are particularly challenging as CH₄ is at low concentration in the atmosphere and large volumes of air must be sampled.

At Imperial College London we developed a unique sampling system for ¹⁴C analysis of atmospheric CH₄ that addresses the sampling challenge, enabling extraction of carbon while sampling and collection of the air sample onto a small trap of molecular sieve (Zazzeri et al. 2021). This system is currently a laboratory prototype and technical developments are needed to make it portable and flexible to user need. The technical changes are being implemented at the Laboratory of Ion Beam Physics at ETH and include: 1) reducing the size of the system components to make the system fully portable, 2) making the sampling procedure fully automated, 3) interfacing the system with the gas ion source of the AMS system Micadas.

Here we present an overview of such developments, with a focus on the testing of a new molecular sieve sample trap. The new sample trap, with a smaller size than the one employed in the original system, will facilitate extraction of the collected carbon for ¹⁴C analysis and will enable direct interfacing with the gas ion source of the AMS system, making ¹⁴CH₄ measurements easier to perform.

Zazzeri, G., Xu, X., & Graven, H. (2021). Environmental Science & Technology, 55(13), 8535-8541.