The Canadian Arctic is warming at an unprecedented rate. Warming-induced permafrost thaw can lead to mobilization of aged carbon from stores in soils and rocks. Tracking the carbon pools supplied to surrounding river networks provides insight on pathways and processes of greenhouse gas release. Here, we investigated the dual-carbon isotopic characteristics of the dissolved inorganic carbon (DIC) pool in the main stem and tributaries of the Mackenzie River system. The radiocarbon (14C) activity of DIC shows export of "old" carbon (2,380 ± 1,040 14C years BP on average) occurred during summer in sampling years. The stable isotope composition of river DIC implicates degassing of aged carbon as CO2 from riverine tributaries during transport to the delta; however, information on potential drivers and fluxes are still lacking. Accounting for stable isotope fractionation during CO2 loss, we show that a large proportion of this aged carbon (60 ± 10%) may have been sourced from biospheric organic carbon oxidation, with other inputs from carbonate weathering pathways and atmospheric exchange. The findings highlight hydrologically connected waters as viable pathways for mobilization of aged carbon pools from Arctic permafrost soils.

The emissions of sulfur dioxide (SO2), a harmful atmospheric pollutant, are on the rise in South Asia. Sulfate, formed from the oxidation of SO2, often comprises 10%–67% of aerosol mass and has a profound impact on climate, air quality/human health, and the environment. The potential drivers of sulfate-linked urban air pollution in South Asian megacities─facing a choking air pollution crisis─remain poorly understood due to a lack of systematic observations. Here, we conducted stable S-isotope (δ34S) fingerprinting of sulfate aerosols in summertime megacity Delhi in South Asia to evaluate the potential drivers. With newly developed region-specific isotopic endmembers in this study, a statistical source apportionment of urban atmospheric sulfate was feasible. Results show that coal combustion (80 ± 12%) and oil combustion (14 ± 11%), followed by road dust (4 ± 3%) and biomass burning (2 ± 2%), were major contributors to atmospheric sulfate in summertime Delhi. Retrospective analysis showed a marked isotopic shift in stable sulfate isotopic composition in summertime megacity Delhi wherein the average δ34S value was 4 ± 1‰ in 2015 and 2 ± 1‰ in 2021, respectively. This was evidently linked to changes in the dominant fuel type as sulfate sourced from coal combustion (oil combustion) significantly increased ∼ 20% (decreased ∼ 20%) during this period. With no clear increase in the number of thermal power plants in and around Delhi, we speculate that the substantial increase in coal-derived sulfate could plausibly be linked to a rise in the informal industries such as brick production and food and agricultural product processing operations, whose SO2 emissions remain challenging to estimate. While further observations from the region are warranted, the findings here suggest that the continued dependence on coal in developing nations of South Asia could be one of the reasons for rising SO2 levels.

The Himalayan Tibetan Plateau (HTP) is one of the world's most climate-sensitive regions outside the polar regions.

The simultaneous monitoring of the triple stable S-isotopes (32S, 33S and 34S) of hydrogen sulfide has been conducted with a VCOF-CRDS set-up (a V-shaped cavity for optical feedback coupled to a cavity ring down spectrometer).

Sulfur isotope analysis provides a unique probe for source-specific information and certain atmospheric reactions. Globally, atmospheric aerosols in urban locations exhibit significant sulfur mass-independent fractionation (i.e., S-MIF, Delta S-33 not equal 0). The origin(s) of these S-MIF anomalies remains unclear, thereby limiting the interpretation and/or application of such signals. Her; we conducted dual-isotope (Delta S-33 and delta S-34) fingerprinting of sulfate aerosols from summertime megacity Delhi in south Asia. A shift toward concomitantly high Delta S-33 (from 0.2 parts per thousand to 0.5 parts per thousand) and low delta S-34 (from 5 parts per thousand to 1 parts per thousand) values was observed with the influx of mineral dust. The Fe:Al ratio showed significant correlations with both sulfate loadings (R-2 = 0.84) and Delta S-33 signatures (R-2 = 0.77). Contrary to the prevailing paradigm, this observational evidence suggests that mineral-dust-associated sulfate exhibits S-MIF anomalies. Atmospheric processing of mineral dust plausibly leads to the production of these anomalies. Our evaluation suggests that an inherent mechanism(s) remains elusive. Although hindered by end-member uncertainties, we show that S-MIF signals can be source apportioned to quantitatively constrain the fraction of mineral-dust-associated sulfate in urban locations. The influx of mineral-dust-associated sulfate can influence urban air pollution affecting air quality and/or human health and as such requires monitoring. Urban Delta S-33 signals can therefore be used to trace this sulfate fraction, thereby improving our understanding of sulfate aerosol dynamics.

Air pollution, a complex cocktail of different components, exerts an influence on climate/human; health both locally and away from source regions. The issue of air pollution is often closely linked; to carbonaceous aerosols, the assessment of climate/air quality/health impact of which remains associated with large uncertainties. Black carbon (BC)—a product of incomplete combustion—is a potent climate warming agent and one of the central components to this issue. An accurate; knowledge of BC emitting sources is necessary for devising appropriate mitigation strategies and; policies to reduce the associated climate/environmental burden. The radiocarbon isotope (14C or carbon-14) fingerprinting allows for an unambiguous and quantitative constraining of the BC sources and is therefore a well-popularized method. Here, we review the existing analytical techniques for the isolation of BC from a filter matrix for conducting 14C-based investigations. This work summarizes the protocols in use, provides an overarching perspective on the state-of- the-art and recommendations for certain aspects of future method development.

Changes in the cosmic-ray background of the Earth can impact the ozone layer. High-energy cosmic events [e.g. supernova (SN)] or rapid changes in the Earth's magnetic field [e.g. geomagnetic Excursion (GE)] can lead to a cascade of cosmic rays. Ensuing chemical reactions can then cause thinning/destruction of the ozone layer-leading to enhanced penetration of harmful ultraviolet (UV) radiation toward the Earth's surface. However, observational evidence for such UV "windows" is still lacking. Here, we conduct a pilot study and investigate this notion during two well-known events: the multiple SN event (approximate to 10kBP) and the Laschamp GE event (approximate to 41kBP). We hypothesize that ice-core-Delta S-33 records-originally used as volcanic fingerprints-can reveal UV-induced background-tropospheric-photochemical imprints during such events. Indeed, we find nonvolcanic S-isotopic anomalies (Delta S-33 not equal 0 parts per thousand) in background Antarctic ice-core sulfate during GE/SN periods, thereby confirming our hypothesis. This suggests that ice-core-Delta S-33 records can serve as a proxy for past ozone-layer-depletion events.

Fine particulate-matter is an important component of air pollution that impacts health and climate, and which delivers anthropogenic contaminants to remote global regions. The complex composition of organic molecules in atmospheric particulates is poorly constrained, but has important implications for understanding pollutant sources, climate-aerosol interactions, and health risks of air pollution exposure. Here, comprehensive nontarget high-resolution mass spectrometry was combined with in silico structural prediction to achieve greater molecular-level insight for fine particulate samples ( n = 40) collected at a remote receptor site in the Maldives during January to April 2018. Spectral database matching identified 0.5% of 60,030 molecular features observed, while a conservative computational workflow enabled structural annotation of 17% of organic structures among the remaining molecular dark matter. Compared to clean air from the southern Indian Ocean, molecular structures from highly-polluted regions were dominated by organic nitrogen compounds, many with computed physicochemical properties of high toxicological and climate relevance. We conclude that combining nontarget analysis with computational mass spectrometry can advance molecular-level understanding of the sources and impacts of polluted air.

South Asian air is among the most polluted in the world, causing premature death of millions and asserting a strong perturbation of the regional climate. A central component is carbon monoxide (CO), which is a key modulator of the oxidizing capacity of the atmosphere and a potent indirect greenhouse gas. While CO concentrations are declining elsewhere, South Asia exhibits an increasing trend for unresolved reasons. In this paper, we use dual-isotope (δ13C and δ18O) fingerprinting of CO intercepted in the South Asian outflow to constrain the relative contributions from primary and secondary CO sources. Results show that combustion-derived primary sources dominate the wintertime continental CO fingerprint (fprimary ∼ 79 ± 4%), significantly higher than the global estimate (fprimary ∼ 55 ± 5%). Satellite-based inventory estimates match isotope-constrained fprimary-CO, suggesting observational convergence in source characterization and a prospect for model-observation reconciliation. This "ground-truthing" emphasizes the pressing need to mitigate incomplete combustion activities for climate/air quality benefits in South Asia.

Aerosol emissions in South Asia are large. The emitted aerosols can travel significant distances and, during the Asian southwest monsoon especially, are prone to modification through cloud processing and wet scavenging while being transported. The scale of emissions and transport means that the global climate impact of these aerosols are sensitive to modification en route, but the process-level understanding is still largely lacking. In this study, we analyse long-term aerosol data measured at an observatory established in Hanimaadhoo, Republic of Maldives, to investigate the long-term properties of aerosols over the Indian Ocean as well as to understand the effect of precipitation on the aerosol particle size distribution during long-range transport. The observatory location is ideal because it is a receptor site with little local influence, and, depending on the season, receives either polluted air masses coming from the Indian subcontinent or clean marine air masses from the Indian Ocean. We analysed the sub-micron particle number size distribution measured during the years 2004–2008, and 2014–2017, and this is the first inter-seasonal long-term study of the sub-micron aerosol features in the region. The aerosol origin and its relative exposure to wet scavenging during long-range transport were analysed using back-trajectory analysis from HYSPLIT. By comparing aerosol measurements to precipitation along its transport, this study shows that there is a substantial change in particle number size distributions and concentrations depending on the amount of rainfall during transport. During the southwest monsoon season, the aerosol size distribution was notably bi-modal and total particle concentrations clearly reduced in comparison with the prevailing aerosol size distribution during the northeast monsoon season. Precipitation during transport usually corresponded with a greater reduction in accumulation mode concentrations than for smaller sizes, and the shape of the median size distribution showed a clear dependence on the trajectory origin and route taken.

Black carbon (BC) aerosols perturb climate and impoverish air quality/human health—affecting ∼1.5 billion people in South Asia. However, the lack of source-diagnostic observations of BC is hindering the evaluation of uncertain bottom-up emission inventories (EIs) and thereby also models/policies. Here, we present dual-isotope-based (Δ14C/δ13C) fingerprinting of wintertime BC at two receptor sites of the continental outflow. Our results show a remarkable similarity in contributions of biomass and fossil combustion, both from the site capturing the highly populated highly polluted Indo-Gangetic Plain footprint (IGP; Δ14C-fbiomass = 50 ± 3%) and the second site in the N. Indian Ocean representing a wider South Asian footprint (52 ± 6%). Yet, both sites reflect distinct δ13C-fingerprints, indicating a distinguishable contribution of C4-biomass burning from peninsular India (PI). Tailored-model-predicted season-averaged BC concentrations (700 ± 440 ng m–3) match observations (740 ± 250 ng m–3), however, unveiling a systematically increasing model-observation bias (+19% to −53%) through winter. Inclusion of BC from open burning alone does not reconcile predictions (fbiomass = 44 ± 8%) with observations. Direct source-segregated comparison reveals regional offsets in anthropogenic emission fluxes in EIs, overestimated fossil-BC in the IGP, and underestimated biomass-BC in PI, which contributes to the model-observation bias. This ground-truthing pinpoints uncertainties in BC emission sources, which benefit both climate/air-quality modeling and mitigation policies in South Asia.

Light-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth's climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (δ13C) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world's largest BrC emission regions-South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by ~84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 ± 0.05 day-1 during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia.