Toward a Standardized Thermal-optical Protocol for Measuring Atmospheric Organic and Elemental Carbon: The EUSAAR Protocol

Thermal-optical analysis is a conventional method for classifying carbonaceous aerosols as organic carbon and elemental carbon. Unfortunately, different thermal evolution protocols result in a wide elemental carbon-to-total carbon variation up to a factor of five. In Europe, there is currently no standard procedure for determining carbonaceous aerosol fraction which implies that data from different laboratories at various sites are most likely not comparable and affected by unknown errors. In the framework of the European project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive work has been carried out to investigate the causes of differences in the EC measured using different thermal evolution protocols and attempts have been devoted to assess and mitigate major positive and negative biases affecting thermal-optical analysis. Our approach to improve the accuracy of the thermal-optical discrimination between organic carbon and elemental carbon was essentially based on four goals. First, as charring correction relies on assumptions proven to be generally not true ¿e.g. pyrolic carbon is considered to evolve completely before native elemental carbon throughout the analysis¿, we sought to reduce pyrolysis to minimum levels in favour of a maximum volatilisation of organic carbon. Second, we sought to minimize the potential negative bias in EC determination caused by early release of light absorbing species at high temperature in the He-mode, including native EC or a combination of EC and pyrolitic carbon with potentially different specific cross section values. Third, we sought to minimize the potential positive bias in EC determination resulting from the slipping of residual organic carbon into the He/O2-mode and its potential evolution after the split point. Finally, we sought to reduce the uncertainty arising from the position of the OC/EC split point on the FID profile through multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200 °C for 120 s; 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 120s, 550°C for 120s, 700°C for 70s, and 850°C for 80s, respectively.JRC.H.2-Climate chang

Results of the second comparison exercise for EU National Air Quality Reference Laboratories (AQUILA) for TC, OC and EC measurement (2011)

The EC-JRC European Reference Laboratory for Air Pollution (ERLAP) has organized an inter-laboratory comparison for the measurement of total carbon (TC), elemental carbon (EC) and organic carbon (OC) in particulate matter collected on filters. To this comparison seventeen European Union National Reference Laboratories for air quality or delegated organizations participated, all using thermal optical analysis with the same analyzer (Sunset Lab off-line carbon analyzer). The aim of this comparison was to evaluate the performances of participants but also to study the effects of applying different thermal protocols, i.e. NIOSH and EUSAAR_2 protocols, currently in use in Europe for such analysis. In absence of a general consensus by the scientific community on the definition of a reference material for EC and, thus, of an standard reference analytical method, method performances [ISO5725-2] and laboratory performances [ISO 13528:2005(E)] were evaluated for TC and EC/TC ratio in the present comparison exercise. For TC, repeatability and reproducibility relative standard deviations ranged from 2% to 6% (sr = 0.017 × m + 0.227) and from 5% to 11% (sR = 0.038 × m + 0.389), respectively. For EC/TC ratio, repeatability and reproducibility relative standard deviations ranged from 2% to 10% and from 8% to 35%, respectively for the NIOSH-like protocol, and from 2% to 14% and from 4% to 19%, respectively for the EUSAAR protocol. (No satisfactory dependence was found upon EC/TC ratio). Furthermore, based on z-scores, three outliers were identified in the TC database when applying as standard deviation for proficiency assessment, σ*, that one calculated from data obtained in a round of a proficiency testing scheme. These outliers would also not comply with the DQO (i.e. expanded uncertainty, with a coverage factor of 2) of 25%, as in the EU Directive 2008/50/EC for PM at its limit value of 50 µg m-3. Laboratory performances were evaluated for EC/TC ratio, separately on the two data subsets from the NIOSH and EUSAAR_2 protocols using as σ* a common level of performance (i.e. 15%) that the inter-laboratory comparison coordinator would wish participants to achieve. Under this condition, four outliers were identified in the subset of data from the NIOSH-like protocol and one outlier in the subset of data from the EUSAAR_2 protocol.JRC.H.2-Air and Climat

Long-term trends in black carbon from biomass and fossil fuel combustion detected at the JRC atmospheric observatory in Ispra

The concentrations of equivalent black carbon deriving from biomass burning [eBC]bb and fossil fuel combustion [eBC]ff have been estimated based on measurements of the aerosol light attenuation at several wavelengths (from infrared to ultraviolet) performed at the atmospheric observatory of the Joint Research Centre located in Ispra (Northern Italy). The data shows repeated seasonal cycles from 2004 to 2016, which suggests that winter time wood burning for domestic heating is the main biomass burning activity in this area. The [eBC]bb/[eBC]ff ratio has increased on average by +5%/yr over the 2007 – 2016 period. We compared these measurement-derived data with CO2 emissions estimated from EDGAR relative to biomass burning for domestic heating and fossil fuel combustion for transport (Diesel) and residential heating (coal + oil) in the 0.4°x0.4° area centred on Ispra. The data shows an increase in CO2 emissions from biomass burning compared to fossil fuel combustion from 2004 to 2008, and a rather constant ratio since then. There is no obvious correlation between the concentrations of [eBC] and the statistics on CO2 emissions from biofuel and fossil fuel combustion over the studied period. The impact of the economic crisis of 2009 on the use of biofuels for domestic heating cannot be rigorously demonstrated, neither from the measurement data nor from the emission inventory.JRC.C.5-Air and Climat

Results of the First EC/OC Comparison Exercise for EU National Air Quality Reference Laboratories (AQUILA)

The JRC-IES European Reference Laboratory for Air Pollution (ERLAP) has organized an inter-laboratory comparison for the measurement of elemental carbon (EC) and organic carbon (OC) in particulate matter sampled on filters. To this comparison European Union National Reference Laboratories for air quality or delegated organizations have participated, all using instrumentation of the same make (Sunset Laboratories Inc. ). The objectives of this comparison have been to evaluate the performances of participants but also to study the effects of the use of different thermal analysis protocols currently used for analysis. It has been shown – based on z-scores – that all participants using laboratory analyzers are able to meet a 25% expanded uncertainty as a “fitness-for-purpose” criterion for total carbon (TC, as the sum of OC and EC) and OC. For EC this criterion is only met when results are evaluated by specific protocols (NIOSH or EUSAAR_2) separately. Field versions of the analyzer have been found for a number of samples to yield aberrant results.JRC.H.2-Air and Climat

Long term trends in aerosol optical characteristics in the Po Valley, Italy

Aerosol properties have been monitored by ground-based in situ and remote sensing measurements at the station for atmospheric research located in Ispra, on the edge of the Po Valley, for almost one decade. In situ measurements are performed according to Global Atmosphere Watch recommendations, and quality is assured through the participation in regular inter-laboratory comparisons. Sunphotometer data are produced by the Aerosol Robotic Network (AERONET). Data show significant decreasing trends over the 2004–2010 period for a number of variables, including particulate matter (PM) mass concentration, aerosol scattering, backscattering and absorption coefficients, and aerosol optical thickness (AOT). In situ measurement data show no significant trends in the aerosol backscatter ratio, but they do show a significant decreasing trend of about −0.7±0.3%yr−1 in the aerosol single scattering albedo (SSA) in the visible light range. Similar trends are observed in the SSA retrieved from sun-photometer measurements. Correlations appear between in situ PM mass concentration and aerosol scattering coefficient, on the one hand, and elemental carbon (EC) concentration and aerosol absorption coefficient, on the other hand. However, no increase in the EC /PM ratio was observed, which could have explained the decrease in SSA. The application of a simple approximation to calculate the direct radiative forcing by aerosols suggests a significant diminution in their cooling effect, mainly due to the decrease in AOT. Applying the methodology we present to those sites, where the necessary suite of measurements is available, would provide important information to inform future policies for air-quality enhancement and fast climate change mitigation.JRC.H.2-Air and Climat

JRC Ispra EMEP - GAW Regional Station for Atmospheric Research - 2005 Report

The aim of the JRC-Ispra station for atmospheric research (45°49'N, 8°38'E) is to monitor atmospheric parameters (pollutant concentrations and fluxes, atmospheric particle chemical composition, number size distribution and optical properties) to contribute in assessing the impact of European policies on air pollution and climate change. The station has been operated continuously since November 1985, with a gap in gas phase data due to a severe breakdown of the data acquisition system in 2003 though. The measurements performed in 2005 led to annual averages of ca. 43 µg m-3 O3, 4 µg m-3 SO2, 16 µg m-3 NO2, 0.8 mg m-3 CO and 41 µg m-3 PM10. Carbonaceous species (organic matter plus elemental carbon) are the main constituents of both PM10 and PM2.5 (> 50%) followed by (NH4)2SO4 and NH4NO3 (a bit less than 20% each). The measurements confirmed the seasonal variations observed over the previous years, mainly driven by meteorology rather than by changes in emissions. Aerosol physical and optical properties were measured from 2004. The average particle number (from 6 nm to 10 µm) was about 10000 cm-3 in 2005. The mean (close to dry) aerosol single scattering albedo (a key parameter for determining the aerosol direct radiative forcing) was 0.80. Long-term trends (over 20 years) show decreases in sulfur concentrations and deposition, and in extreme ozone value occurrence frequency. The decreasing trends in nitrogen oxides, reduced nitrogen species, and PM concentrations are much less marked.JRC.H.2-Climate chang

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

JRC Ispra EMEP-GAW Regional Station for Atmospheric Research - 2007 Report

The aim of the JRC-Ispra station for atmospheric research (45°49'N, 8°38'E) is to monitor atmospheric parameters (pollutant concentrations and fluxes, atmospheric particle chemical composition, number size distribution and optical properties) to contribute in assessing the impact of European policies on air pollution and climate change. The station has been operated continuously since November 1985, with a gap in gas phase data due to a severe breakdown of the data acquisition system in 2003 though. The measurements performed in 2007 led to annual averages of ca. 32 µg m-3 O3, 0.8 µg m-3 SO2, 21 µg m-3 NO2 and 30 µg m-3 PM10. Carbonaceous species (organic matter plus elemental carbon) are the main constituents of PM2.5 (> 55 %) followed by NH4NO3 (20-30 %) and (NH4)2SO4 (10-20 %). The measurements confirmed the seasonal variations observed over the previous years, mainly driven by meteorology rather than by changes in emissions. Aerosol physical and optical properties were also measured in 2007. The average particle number (from 10 nm to 10 µm) was about 9200 cm-3 in 2007. The mean (close to dry) aerosol single scattering albedo (0.79) was low compared to the values generally observed in Europe, which means that the cooling effect of aerosols is reduced in our region compared to others. Long-term trends (over 20 years) show consistent decreases in sulfur concentrations and deposition, PM mass concentration (-0.9 µg m-3 yr-1) and in extreme ozone value occurrence frequency. The decreasing trends in oxidised and reduced nitrogen species are much less pronounced. However, historical minimum in NO3-, NH4+, (and SO42-) wet deposition, as well as in O3 pollution indicators (AOT40 and SOMO35) were observed in 2007.JRC.H.2-Climate chang

JRC Ispra EMEP - GAW Regional Station for Atmospheric Research - 2006 Report

The aim of the JRC-Ispra station for atmospheric research (45°49'N, 8°38'E) is to monitor atmospheric parameters (pollutant concentrations and fluxes, atmospheric particle chemical composition, number size distribution and optical properties) to contribute in assessing the impact of European policies on air pollution and climate change. The station has been operated continuously since November 1985, with a gap in gas phase data due to a severe breakdown of the data acquisition system in 2003 though. The measurements performed in 2006 led to annual averages of ca. 41 µg m-3 O3, 1.1 µg m-3 SO2, 21 µg m-3 NO2 and 33 µg m-3 PM10. Carbonaceous species (organic matter plus elemental carbon) are the main constituents of PM2.5 (> 50 %) followed by (NH4)2SO4 (10-20 %) and NH4NO3 (20-30 %). The measurements confirmed the seasonal variations observed over the previous years, mainly driven by meteorology rather than by changes in emissions. Aerosol physical and optical properties were also measured in 2006. The average particle number (from 6 nm to 10 µm) was about 10000 cm-3 in 2006. The mean (close to dry) aerosol single scattering albedo (a key parameter for determining the aerosol direct radiative forcing) was 0.79. Long-term trends (over 20 years) show decreases in sulfur concentrations and deposition, and in extreme ozone value occurrence frequency, although the latter was higher in compared to the last two years The decreasing trends in nitrogen oxides, reduced nitrogen species, and PM concentrations are much less pronounced.JRC.H.2-Climate chang