G01_01

Atmospheric ¹⁴CO₂ time series from Point Barrow, Alaska: ending of the “Bomb Radiocarbon Period” in the Northern Hemisphere

Xu X¹, Walker J², Newman S^3,5, Trumbore S^1,4

¹Keck Carbon Cycle AMS Lab, Department of Earth System Science, University of California, Irvine, Irvine, United States, ²André E. Lalonde AMS Laboratory, University of Ottawa, Ottawa, Canada, ³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA, ⁴Department Biogeochemical Processes, Max-Planck-Institute for Biogeochemistry, Jena, Germany, ⁵Bay Area Air Quality Management District, San Francisco, USA

The distribution rate and pattern of ¹⁴C produced by nuclear weapons testing during late 1950s – early 1960s has provided a unique opportunity for tracing global carbon cycles, and also for studying atmospheric mixing. The atmospheric ¹⁴CO₂ peaked around 1964, and since then has decreased as excess ¹⁴C cycled between atmospheric, oceanic and terrestrial carbon reservoirs and was diluted by fossil fuel CO₂ addition to the atmosphere. In this century, fossil fuel dilution has become the major factor controlling the rate of decrease in the atmospheric ¹⁴CO₂.

We report a continuous, high precision and high temporal resolution Δ¹⁴CO₂ record from Barrow, Alaska (71°N, 157°W) from 2003 to 2022. Sample collection was through the NOAA/ESRL flask sampling network program, which enables comparison of radiocarbon data with other trace gases and isotopes, including CO and CO₂ mixing ratios and δ¹³C and δ18O of CO₂. There are distinct Δ¹⁴CO₂ seasonal cycles in this record, with a broad minimum around Mar-Apr and a maximum in Sep-Oct with an amplitude of ~7‰. From 2003 to the end of 2019, Δ¹⁴CO₂ decreased linearly by ~4.3‰/year, although it slowed during 2020 which may likely have resulted from reduced fossil fuel CO₂ emission during the global lockdown imposed by the COVID-19 pandemic. By the end of 2021, Δ¹⁴CO₂ at Barrow declined to below 0‰, ending the “Bomb Radiocarbon Period” in the Northern Hemisphere. This iconic event is of global significance because the artificial “aging” of the atmosphere has the potential to affect many radiocarbon applications in the future.

G01_02

Tracking changes in fossil fuel CO₂ emissions using citizen science supported radiocarbon observations

Turnbull J^1,2, Domingues L¹, Turton N¹

¹GNS Science, Lower Hut, New Zealand, ²CIRES, University of Colorado, Boulder, USA

Emissions from on road transportation are one of the largest sources of fossil fuel CO₂ globally.  For many cities, they are the largest single emission source, and hence are a primary target for mitigation actions not only to reduce fossil fuel CO₂ emissions, but adding the co-benefits of reduced traffic, reduced reliance on fuel imports and cleaner air.

Mitigation strategies include improved vehicle efficiency, transition to electric vehicles, and traffic reduction strategies.

The travel and work restrictions imposed by COVID-19 lockdowns resulted in dramatic changes in fossil fuel CO₂ emissions around the world, most prominently in the transportation sector.  This provided an ideal opportunity to test our ability to observe and quantify local changes in fossil fuel CO₂ emissions.  We used a novel citizen science campaign to collect grass samples from around New Zealand and use radiocarbon measurements to quantify the recently added, local, fossil fuel CO₂ mole fraction at the local and time period that the grass grew. 

Our results from 17 sites in five cities around New Zealand demonstrate dramatic reductions in traffic emissions of 75 ± 3 % during the most severe lockdown restriction period.  The less restrictive 2021 lockdown resulted in spatially variable transportation emission reductions, apparently due to local traffic patterns and traffic flow. Overall, the grass sampling methodology gives surprisingly robust results, engages the community and policy makers, and provides a straightforward method for evaluating the impact of local-scale emission mitigation strategies.

G01_03

Investigating the variability in the CO:CO₂ff emission ratio at different site types and times of day in Auckland, New Zealand

Young H¹, Turnbull J^1,2, Keller E^1,3, Domingues L¹, Parry-Thompson J¹, Hilton T¹

¹GNS Science, Wellington, New Zealand, ²University of Colorado, Boulder,, USA, ³Antarctic Research Centre, Wellington, New Zealand

Cities occupy just 3% of Earth’s surface area yet contribute ~70% of the world’s fossil fuel CO₂ (CO₂ff) emissions resulting in them becoming focal points for observing emissions. While it is difficult to determine CO₂ff emissions from CO₂ measurements alone, radiocarbon in CO₂ (¹⁴CO₂) is an excellent tracer for CO₂ff. Carbon monoxide (CO) is produced as a by-product of combustion, with each emission source producing a varying amount of CO and CO₂ff, reported as the CO:CO₂ff emission ratio. By combining CO and ¹⁴CO₂ measurements, it is possible to evaluate local source types as each has its own unique signature.

As part of the CarbonWatch-NZ research programme, air samples were collected in flasks around Auckland and measured to determine CO:CO₂ff at 28 sites over four years. Samples were grouped by location to provide overall emission ratios for each site type (motorway, urban, suburban, and industrial). The emission ratios were then used to identify and compare local CO₂ff sources at each site type. Since vehicles are major contributors to city emissions, CO:CO₂ff for traffic is especially useful. Flasks collected at motorway sites showed emission ratios consistent with expectations for traffic.  Suburban and light industrial locations showed ratios consistent with traffic as the dominant CO₂ff source. Urban areas showed a smaller ratio, reflecting a larger CO₂ff contribution from other sources. This observed distribution of sources provides an independent validation of the expected CO₂ff emission sources determined from the Mahuika high-resolution CO₂ff inventory for Auckland.

G01_04

Fifty-five years of radiocarbon studies in Bratislava: From the atmosphere to tree rings and wines

Povinec P¹, Kontuľ I¹, Šivo A¹, Ješkovský M¹, Kaizer J¹, Kvasniak J¹, Richtáriková M¹, Zeman J¹

¹Comenius University, Department s of Nuclear Physics and Biophysics, Bratislava, Slovakia

Radiocarbon investigations in Bratislava started in 1966 with the aim to develop techniques for sampling and measurement of C-14 levels in the air around a nuclear power plant (NPP) which was under construction in Jaslovské Bohunice, about 60 km NE from Bratislava. Simultaneously, a background monitoring station was established in Bratislava to identify contributions from combustion of fossil fuels and possible emissions from the Jaslovské Bohunice NPP. A correlation has been found between atmospheric radiocarbon data measured at both stations when there was a favorable transport of air masses from Jaslovské Bohunice to Bratislava. The radiocarbon concentrations in the heavily polluted atmosphere of Bratislava were during eighties by about 100‰ and at Jaslovské Bohunice by about 50‰ lower than the European clean air represented by the Jungfraujoch radiocarbon data. After 1994, when the industrial activities in the region decreased, the radiocarbon concentrations were similar at both sites, and from 2000 they were close to the European clean air levels. Annual tree rings have been used later as archives of past radiocarbon levels in the biosphere either for solar activity studies or for investigations of fossil fuel and NPP emissions. Atmospheric and tree ring data from the Jaslovské Bohunice NPP were compared with those measured in the polluted Bratislava, as well as with two background monitoring stations. Wine samples have also been found as good archives of past radiocarbon levels in the atmosphere. Their ability to record and preserve past radiocarbon levels has also been utilized for dating of old wines.

G01_05

Atmospheric ¹⁴CO₂ observations in megacity Delhi: Inferences for fossil fuel CO₂ (CO₂ff ) emissions

Sharma R¹, Kumar Kunchala R¹, Ojha S², Kumar P², Gargari S², Chopra S²

¹Indian Institute of Technology Delhi, New Delhi, India, ²Inter University Accelerator Centre, New Delhi, India

Radiocarbon is an ideal tracer for fossil fuel CO₂ estimations in the atmosphere because of its absence in the fossil fuels. It is formed in the atmosphere by the interaction of cosmic rays with ¹⁴N atoms and distributed in the different reservoirs of earth systems in the form of ¹⁴CO₂. In present study, we have presented the analysis on the fossil fuel CO₂ emissions in megacity Delhi using ¹⁴CO₂ observations for the period from 2017 to 2022. Weekly and sub-weekly integrated atmospheric CO₂ samples are collected in the form of carbonates by absorbing CO₂ over sodium hydroxide at accelerator mass spectrometry (AMS) facility building in Inter University Accelerator Centre (IUAC), New Delhi. These carbonate samples are acid hydrolyzed using carbonate handling system (CHS) and graphitized using automated graphitization equipment (AGE). Radiocarbon in the form of ¹⁴C/¹²C ratio is measured using a 500 kV ion accelerator at IUAC – AMS facility with the precision between 2 to 3 ‰ and measured ¹⁴C/¹²C ratios are converted into Δ¹⁴C values and CO₂ff values are calculated using Δ¹⁴C values. Results of this study in terms of annual and seasonal variations of Δ¹⁴C and CO₂ff will be presented for the study period over Delhi. Correlations of Δ¹⁴C and CO₂ff with other pollutant concentrations (PM2.5, CO, NO₂, SO₂ etc.) from the nearest air quality monitoring stations and available bottom up CO₂ff inventories will also be discussed.

G01_06

Radiocarbon Inventories of Switzerland (RICH) : Source apportionment of atmospheric CO₂, sampling strategy and first results

Geissbühler D^1,2, Laemmel T^1,2, Gautschi P³, Wacker L³, Szidat S^1,2

¹Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland, ²Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ³Laboratory of Ion Beam Physics, Institute for Particle Physics and Astrophysics, Federal Institute of Technology Zurich (ETHZ), Zurich, Switzerland

Anthropogenically-induced climate change is strongly linked with perturbations of the carbon cycle causing the emission of greenhouse gases into the atmosphere, especially carbon dioxide (CO₂). Radiocarbon (¹⁴C) measurements of atmospheric CO₂ are unique in their capabilities to provide information on carbon source apportionment and transport, especially of fossil-fuel derived CO₂ which is ¹⁴C-free.

The Radiocarbon Inventories of Switzerland (RICH) project aims to build a comprehensive database and model of the distribution and cycling of radiocarbon in Switzerland across the atmosphere, soils, rivers and lakes. The project presented here will serve to specifically construct an inventory of atmospheric ¹⁴CO₂ in this larger scope. This will be achieved by sampling air in strategic ways, and measuring its ¹⁴CO₂ content, as well as CO₂ concentration. This will bring information on the radiocarbon signature of concentrated anthropogenic emissions in air masses, the spatial representation of diffuse natural emissions in multiple ecosystems, as well as their subsequent atmospheric transport. One of the main challenge in this work is to develop a robust sampling method allowing us to effectively capture ¹⁴CO₂ signatures. Graphitization of air samples will be done by using the Air Loading Facility developed at ETHZ (Gautschi, 2017). Measurements from leaf biomass are also planned, which will allow an insight into the integration of ¹⁴CO₂ to the vegetation, and ultimately to soils.

Presented here are the current status of the sampling methods and strategy development, as well as results from the first campaigns.

G01_07

Atmospheric ¹⁴CH₄ measurements over Switzerland: first data and modeling results

Laemmel T^1,2, Geissbühler D^1,2, Espic C^1,2, Bantle M¹, Leuenberger M^2,3, Henne S⁴, Brunner D⁴, Szidat S^1,2

¹Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Bern, Switzerland, ²Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ³Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland, ⁴Empa, Laboratory for Air Pollution/Environmental Technology, Dübendorf, Switzerland

Methane (CH₄) is the second most important anthropogenic greenhouse gas after carbon dioxide (CO₂). While biogenic emissions of CH₄ contain present-day radiocarbon (¹⁴C) levels, CH₄ derived from fossil sources is ¹⁴C-free so that ¹⁴CH₄ measurements can be used as a source apportionment proxy to distinguish anthropogenic from biogenic CH₄ sources. Recently, a new methane preconcentration and purification setup (MPPS) was developed at the Laboratory for the Analysis of Radiocarbon with AMS, University of Bern (Espic et al., 2019). Typical samples are 60L of atmospheric air collected in bags, resulting after extraction in about 60 µg carbon in CH₄-derived CO₂ form, enough for a ¹⁴C gas measurement on a MICADAS (Mini Carbon Dating System) accelerator mass spectrometer.

This contribution presents the new MPPS, its performance and ¹⁴CH₄ measurements of biweekly air samplings at four sites in Switzerland, for most of them continuously since 2019: the high altitude research station Jungfraujoch considered as a European continental background station, two tall towers in Beromünster and Sottens and an urban site in Bern. The CH₄ source apportionment at these sites is challenged by sporadic transport of ¹⁴CH₄ emitted from pressurized water reactors of nuclear power plants in Switzerland and neighboring countries. To identify and filter out these situations, forward simulations of atmospheric ¹⁴CH₄ transport using the model FLEXPART-COSMO, including nuclear power plants emissions, are applied.

This sampling strategy is part of the ongoing project RICH (Radiocarbon Inventories of Switzerland) aiming to develop a national radiocarbon inventory in the atmospheric, terrestrial and aquatic carbon pools.

G01_09

Quantitative evaluation of OC aerosol sources and aging processes: insights from a comprehensive method of dual-carbon isotopes and tracers

Jiang F^1,6, Liu J¹, Cheng Z^2,7, Ding P^3,7, Zhu S^2,7, Yuan X¹, Zhang Z⁴, Zong Z⁵, Tian C⁵, Hu W^2,7, Zheng J¹, Szidat S⁶, Li J^2,7, Zhang G^2,7

¹Institute for Environmental and Climate Research, Jinan University, Guangzhou, China, ²State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, ³State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, ⁴South China Institute of Environmental Sciences, Ministry of Environmental Protection, Guangzhou, China, ⁵Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China, ⁶Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ⁷CAS Center for Excellence in Deep Earth Science, Guangzhou, China

Organic carbon aerosol (OC) is a pivotal component of PM₂.₅ in the atmospheric environment, yet its emission sources and atmospheric behaviors remain poorly constrained. In this study, a comprehensive method based on the combination of dual-carbon isotopes (¹³C and ¹⁴C) and macro tracers was employed in the PRDAIO campaign performed in the megacity Guangzhou, China. The ¹⁴C analysis showed that ~60 % of OC during the sampling campaign was associated with non-fossil sources such as biomass burning activities and biogenic emissions. It should be noted that this non-fossil contribution in OC would significantly decrease when the air masses came from the eastern cities. Overall, non-fossil secondary OC was the largest contributor (~39 %) to OC, followed by fossil secondary OC (~26 %), non-fossil primary OC (~21 %), and fossil primary OC (~14 %). Also, we established the dynamic variation of ¹³C as a function of aged OC and VOCs oxidized OC to explore the aging processes of OC. Our pilot results showed that a large fraction (average: ~53 %) of OC was not from the gaseous oxidation but the aging formation. This study confirmed that non-fossil sources played an important role in the loading of organic aerosol in this megacity and the aging processes were probably highly involved in the formation of organic aerosol.

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_P11

Using ¹⁴CO₂ to derive fossile fule CO₂ in the UK.

Wenger A¹, Knowles T¹, Chawner H¹, RIgby M¹, O'Doherty S¹

¹University Of Bristol, Bristol, United Kingdom

Estimating the anthropogenic component of carbon dioxide emissions from direct measurements is difficult, due to the large natural carbon dioxide fluxes. One way of determining the fossil fuel component of atmospheric carbon dioxide is the use of radiocarbon measurements, as carbon from fossil fuel is completely devoid of radiocarbon due to its age. 

The DARE-UK project is attempting to use high frequency ¹⁴CO₂ observations at atmospheric observation sites to infer UK fossil fuel emissions.

We will present the first year of atmospheric ¹⁴CO₂ data from 2 UK sites and a background site in Ireland. To cope with the large sample volume, we partially automated the ¹⁴CO₂ sample preparation by developing an automated CO₂ extraction system, that interlinks with a commercially available graphitization system.

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.