An optimised organic carbon ∕ elemental carbon (OC ∕ EC) fraction separation method for radiocarbon source apportionment applied to low-loaded Arctic aerosol filters

Radiocarbon (14C) analysis of carbonaceous aerosols is used for source apportionment, separating the carbon content into fossil vs. non-fossil origin, and is particularly useful when applied to subfractions of total carbon (TC), i.e. elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC), and water-insoluble OC (WINSOC). However, this requires an unbiased physical separation of these fractions, which is difficult to achieve. Separation of EC from OC using thermal–optical analysis (TOA) can cause EC loss during the OC removal step and form artificial EC from pyrolysis of OC (i.e. so-called charring), both distorting the 14C analysis of EC. Previous work has shown that water extraction reduces charring. Here, we apply a new combination of a WSOC extraction and 14C analysis method with an optimised OC/EC separation that is coupled with a novel approach of thermal-desorption modelling for compensation of EC losses. As water-soluble components promote the formation of pyrolytic carbon, water extraction was used to minimise the charring artefact of EC and the eluate subjected to chemical wet oxidation to CO2 before direct 14C analysis in a gas-accepting accelerator mass spectrometer (AMS). This approach was applied to 13 aerosol filter samples collected at the Arctic Zeppelin Observatory (Svalbard) in 2017 and 2018, covering all seasons, which bear challenges for a simplified 14C source apportionment due to their low loading and the large portion of pyrolysable species. Our approach provided a mean EC yield of 0:87±0:07 and reduced the charring to 6.5% of the recovered EC amounts. The mean fraction modern (F14C) over all seasons was 0.85±0.17 for TC; 0.61±0.17 and 0.66±0.16 for EC bebefore and after correction with the thermal-desorption model, respectively; and 0.81±0.20 for WSOC

Toward a Standardised Thermal-Optical Protocol for Measuring Atmospheric Organic and Elemental Carbon: The EUSAAR Protocol

Thermal-optical analysis is a conventional method for determining the carbonaceous aerosol fraction and for classifying it into organic carbon, OC, and elemental carbon, EC. Unfortunately, the different thermal evolution protocols in use can result in a wide elemental carbon-to-total carbon variation by up to a factor of five. In Europe, there is currently no standard procedure for determining the carbonaceous aerosol fraction which implies that data from different laboratories at various sites are of unknown accuracy and cannot be considered comparable. In the framework of the EU-project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive study has been carried out to identify the causes of differences in the EC measured using different thermal evolution protocols; thereby the major positive and negative biases affecting thermal-optical analysis have been isolated and minimised to define an optimised protocol suitable for European aerosols. Our approach to improve the accuracy of the discrimination between OC and EC was essentially based on four goals. Firstly, charring corrections rely on faulty assumptions ¿e.g. pyrolytic carbon is considered to evolve completely before native EC throughout the analysis¿, thus we have reduced pyrolysis to a minimum by favoring volatilisation of OC. Secondly, we have minimised the potential negative bias in EC determination due to early evolution of light absorbing carbon species at higher temperatures in the He-mode, including both native EC and combinations of native EC and pyrolytic carbon potentially with different specific cross section values. Thirdly, we have minimised the potential positive bias in EC determination resulting from the incomplete evolution of OC during the He-mode which then evolves during the He/O2-mode, potentially after the split point. Finally, we have minimised the uncertainty due to the position of the OC/EC split point on the FID response profile by introducing multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we have defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200°C for 120s; step 2 in He 300°C for 150s; step 3 in He 450°C for 180s; step 4 in He 650°C for 180s. For steps 1-4 in He/O2, the conditions are 500°C for 120 s, 550°C for 120s, 700°C for 70s, and 850°C for 80s, respectively.JRC.DDG.H.2-Climate chang

Health effects of residential wood smoke particles: the importance of combustion conditions and physicochemical particle properties

Background: Residential wood combustion is now recognized as a major particle source in many developed countries, and the number of studies investigating the negative health effects associated with wood smoke exposure is currently increasing. The combustion appliances in use today provide highly variable combustion conditions resulting in large variations in the physicochemical characteristics of the emitted particles. These differences in physicochemical properties are likely to influence the biological effects induced by the wood smoke particles. Outline: The focus of this review is to discuss the present knowledge on physicochemical properties of wood smoke particles from different combustion conditions in relation to wood smoke-induced health effects. In addition, the human wood smoke exposure in developed countries is explored in order to identify the particle characteristics that are relevant for experimental studies of wood smoke-induced health effects. Finally, recent experimental studies regarding wood smoke exposure are discussed with respect to the applied combustion conditions and particle properties. Conclusion: Overall, the reviewed literature regarding the physicochemical properties of wood smoke particles provides a relatively clear picture of how these properties vary with the combustion conditions, whereas particle emissions from specific classes of combustion appliances are less well characterised. The major gaps in knowledge concern; (i) characterisation of the atmospheric transformations of wood smoke particles, (ii) characterisation of the physicochemical properties of wood smoke particles in ambient and indoor environments, and (iii) identification of the physicochemical properties that influence the biological effects of wood smoke particles

Contribution of fluorescent primary biological aerosol particles to low-level Arctic cloud residuals

Mixed-phase clouds (MPCs) are key players in the Arctic climate system due to their role in modulating solar and terrestrial radiation. Such radiative interactions rely, among other factors, on the ice content of MPCs, which is regulated by the availability of ice-nucleating particles (INPs). While it appears that INPs are associated with the presence of primary biological aerosol particles (PBAPs) in the Arctic, the nuances of the processes and patterns of INPs and their association with clouds and moisture sources have not been resolved. Here, we investigated for a full year the abundance of and variability in fluorescent PBAPs (fPBAPs) within cloud residuals, directly sampled by a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory (475 m a.s.l.) in Ny-Ålesund, Svalbard. fPBAP concentrations (10−3–10−2 L−1) and contributions to coarse-mode cloud residuals (0.1 to 1 in every 103 particles) were found to be close to those expected for high-temperature INPs. Transmission electron microscopy confirmed the presence of PBAPs, most likely bacteria, within one cloud residual sample. Seasonally, our results reveal an elevated presence of fPBAPs within cloud residuals in summer. Parallel water vapor isotope measurements point towards a link between summer clouds and regionally sourced air masses. Low-level MPCs were predominantly observed at the beginning and end of summer, and one explanation for their presence is the existence of high-temperature INPs. In this study, we present direct observational evidence that fPBAPs may play an important role in determining the phase of low-level Arctic clouds. These findings have potential implications for the future description of sources of ice nuclei given ongoing changes in the hydrological and biogeochemical cycles that will influence the PBAP flux in and towards the Arctic.</p

Physical and chemical characterization of the particulate matter suspended in aerosols from the urban area of Belgrade

Within this study, attempts were made to characterize the coarse and fine particulate aerosol fractions in urban area of Belgrade and define the inorganic chemical composition of the aerosol fractions. For this purpose, daily deposits Of PM(10), PM(2.5) and PM(1) aerosol fractions were collected during spring and autumn sampling periods in 2007 and analyzed for the PM mass concentrations, trace elements and secondary ions. The results obtained in the two campaigns showed average daily mass concentrations of 37 and 44 mu g/m(3) for PM(10), 22 and 23 mu g/m(3) for PM(2.5) and 15 and 17 mu g/m(3) for the finest particulate matter fraction PM(1) with the maximums exceeding the limit values set by the EU air quality regulations. A correlation with the gas-phase ambient air pollutants SO(2), NO(2) and O(3) was found and is discussed. The concentrations of trace elements (Mg, Al, K, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sb, Ba, Tl, Pb and Th) and secondary ions (NO(3)(-), SO(4)(2-), NH(4)(+), K(+), Ca(2+) and Na(+)) determined in the PM(10), PM(2.5) and PM(1) aerosol fractions showed levels and distributions indicating soil and traffic-related sources as the main pollution sources. This study was conducted as the first step of PM assessment in order to point out main air pollution sources and suggest a remedy strategy specific for this region

Variations of Pm10 Mass Concentrations and Correlations with Other Pollutants in Belgrade Urban Area

In this paper, we present the PM10 levels measured at an urban residential background site in New Belgrade in Omladinskih Brigada Street, at 15 m height (roof) The aerosol samples were collected using a European standard sampler in four seasonal campaigns conducted in autumn Nov 13-Dec 03 2007 winter Feb 07-28, 2008 spring May 06-28, 2008 and summer July 17-August 15 2008 The results were compared with PM10 mass concentrations measured with a Horiba automatic station at street level at the same sampling site and at three more sites within the Belgrade municipal monitoring network The results show that the PM10 values in the Belgrade urban area were high during autumn and winter campaigns (heating season) with a number of samples exceeding the 24-h limit value of 50 mu g m(3) On the roof station, a maximum daily value of 209 mu g m(3) was measured in the autumn campaign, with 14 values out of 20 measurements exceeding the 24-h limit In winter, 14 out of 19 measurements exceeded the limit, with a maximum value of 196 mu g m(3) During the spring campaign, the number of exceedances was three out of 22 All values during the summer campaign were below 50 mu g m(3) The roof station equipped with the European Standard instrument showed systematically higher values than the street-level automatic monitor PM10 values at all sites followed the same trend The highest concentrations at all monitoring sites were observed during the autumn, Nov 20-25, 2007, and winter, Feb 19-23, 200

Measurement of Elemental and Organic Carbon in Europe

The new Air Quality Directive 2008/50/EC is asking in Annex IX that elemental (EC) and organic (OC) carbon as well as soluble ions should be measured at selected background sites in each Member State. Several methods (thermal, optical or photo-acoustic methods) to determine elemental and organic carbon exist which do not always deliver comparable results. European experts in EC/OC measurements met at the JRC in Ispra on 10th and 11th February 2009 to discuss during a workshop the best suitable European method. The main tasks of this workshop were to discuss the advantages and disadvantages of different methods for the determination of OC and EC, to get information from the Member States on existing methods or even standards being applied, to initiate discussions on a preferred basic method to be standardised by CEN within the scope of Directive 2008/50/EC. The conclusions of this workshop will directly feed into CEN and the corresponding Working Group to clearly define their task for European wide standardisation and hence harmonisation.JRC.H.4-Transport and air qualit

Elucidating the present-day chemical composition, seasonality and source regions of climate-relevant aerosols across the Arctic land surface

The Arctic is warming two to three times faster than the global average, and the role of aerosols is not well constrained. Aerosol number concentrations can be very low in remote environments, rendering local cloud radiative properties highly sensitive to available aerosol. The composition and sources of the climate-relevant aerosols, affecting Arctic cloud formation and altering their microphysics, remain largely elusive due to a lack of harmonized concurrent multi-component, multi-site, and multi-season observations. Here, we present a dataset on the overall chemical composition and seasonal variability of the Arctic total particulate matter (with a size cut at 10 mu m, PM10, or without any size cut) at eight observatories representing all Arctic sectors. Our holistic observational approach includes the Russian Arctic, a significant emission source area with less dedicated aerosol monitoring, and extends beyond the more traditionally studied summer period and black carbon/sulfate or fine-mode pollutants. The major airborne Arctic PM components in terms of dry mass are sea salt, secondary (non-sea-salt, nss) sulfate, and organic aerosol (OA), with minor contributions from elemental carbon (EC) and ammonium. We observe substantial spatiotemporal variability in component ratios, such as EC/OA, ammonium/nss-sulfate and OA/nss-sulfate, and fractional contributions to PM. When combined with component-specific back-trajectory analysis to identify marine or terrestrial origins, as well as the companion study by Moschos et al 2022 Nat. Geosci. focusing on OA, the composition analysis provides policy-guiding observational insights into sector-based differences in natural and anthropogenic Arctic aerosol sources. In this regard, we first reveal major source regions of inner-Arctic sea salt, biogenic sulfate, and natural organics, and highlight an underappreciated wintertime source of primary carbonaceous aerosols (EC and OA) in West Siberia, potentially associated with the oil and gas sector. The presented dataset can assist in reducing uncertainties in modelling pan-Arctic aerosol-climate interactions, as the major contributors to yearly aerosol mass can be constrained. These models can then be used to predict the future evolution of individual inner-Arctic atmospheric PM components in light of current and emerging pollution mitigation measures and improved region-specific emission inventories.Peer reviewe