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

Literature review for ODS (Ozone Depleting Substances) measurement methods and data

Stratospheric ozone absorbs most of the sun’s harmful UV radiation. The increased use of human-produced gases such as chlorofluorocarbons (CFCs) has led to a magnified springtime depletion of the protective ozone layer at both Earth’s poles, especially over Antarctica, a phenomenon well known as the ozone hole. The Montreal protocol [1] deals with substances that deplete the ozone layer (ODS) and how to reduce them (Montreal protocol, 1987 and amendments/adjustments). It covers substances with a high ozone depleting potential, CFCs and the 1st generation of CFC replacements (HCFCs). The success of the implementation of the Montreal protocol and amendments has to be demonstrated by the parties (including EU and its Member States [2]), and supported by high quality atmospheric measurements of relevant compounds. Several atmospheric data-sets are available from open-access international data bases, including 7 stations across Europe: (1) Zeppelin, Ny-Ålesund, Norway, (2) Summit, Greenland, Denmark, (3) Mace Head, Ireland, (4) Tacolneston, UK, (5) Jungfraujoch, Switzerland, (6) Monte Cimone, Italy, and (7) Lampedusa (LMP), Italy, but data quality may in some cases be unknown or questionable. High-quality long-term ambient air data are mainly coming from the AGAGE Network (http://agage.mit.edu/ [3]) and NOAA (National Oceanic and Atmospheric Administration). Ref. [3] comprising also European stations from e.g. (I) Ireland (first Agrigole (1978-1983), then Mace Head (from 1987 to present), (II) Switzerland (Jungfraujoch), from 2000 to present, (III) Norway (Ny Ålesund), from 2000 to present, and (IV) Italy (Monte Cimone) from 2002 to present. The trends in ODS concentrations measured in-situ at ground level in Europe are consistent and, similar to the trends observed in the rest of the world (see ref. [4] containing in-situ ground level measurements, flask sampling and satellite observations), especially the downwards trend of CFCs, indicating the success of the Montreal Protocol, in limiting the atmospheric abundances of ODSs [4]. The UNEP/WMO Scientific Assessment of Ozone Depletion from 2014 states [4]: “The success of the Montreal Protocol in limiting the atmospheric abundances of ODSs is now well documented”. This is confirmed by the AGAGE measurement network [3]: “International compliance with the Montreal Protocol is so far resulting in CFC and chlorocarbons abundances comparable to the target level so the Protocol is working”. In contrast, it is of concern that the concentrations of HCFCs and N2O, where the latter one being currently the single most important gas that depletes stratospheric ozone (see e.g. ref. Ravishankara et al., 2009 [15], and discussions in this report), are still increasing.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

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

Lidar and in situ observations of continental and Saharan aerosol: closure analysis of particles optical and physical properties

Single wavelength polarization lidar observations collected at Mt. Cimone (44.2º N, 10.7º E, 1870 m a.s.l.) during the June 2000 MINATROC campaign are analyzed to derive tropospheric profiles of aerosol extinction, depolarization, surface area and volume. Lidar retrievals for the 2170-2245 m level are compared to the same variables as computed from in situ measurements of particles size distributions, performed at the mountain top Station (2165 m a.s.l.) by a differential mobility analyzer (DMA) and an optical particle counter (OPC). A sensitivity analysis of this closure experiment shows that mean relative differences between the backscatter coefficients obtained by the two techniques undergo a sharp decrease when hygroscopic growth to ambient humidity is considered for the DMA dataset, otherwise representative of dry aerosols. Minimization of differences between lidar and size distribution-derived backscatter coefficients allowed to find values of the "best" refractive index, specific to each measurement. These results show the refractive index to increase for air masses proceeding from Africa and Western Europe. Lidar depolarization was observed to minimize mainly in airmasses proceeding from Western Europe, thus indicating a spherical, i.e. liquid nature for such aerosols. Conversely, African, Mediterranean and East Europe aerosol showed a larger depolarizing fraction, mainly due to coexisting refractory and soluble fractions. The analysis shows average relative differences between lidar and in-situ observations of 5% for backscatter, 36% for extinction 41% for surface area and 37% for volume. These values are well within the expected combined uncertainties of the lidar and in situ retrievals. Average differences further decrease during the Saharan dust transport event, when a lidar signal inversion model considering non-spherical scatterers is employed. The quality of the closure obtained between particle counter and lidar-derived aerosol surface area and volume observations constitutes a validation of the technique adopted to retrieve such aerosol properties on the basis of single-wavelength lidar observations

Comparison of source apportionment approaches and analysis of non-linearity in a real case model application

Abstract. The response of particulate matter (PM) concentrations to emission reductions was analysed by assessing the results obtained with two different source apportionment approaches. The brute force (BF) method source impacts, computed at various emission reduction levels using two chemical transport models (CAMx and FARM), were compared with the contributions obtained with the tagged species (TS) approach (CAMx with the PSAT module). The study focused on the main sources of secondary inorganic aerosol precursors in the Po Valley (northern Italy): agriculture, road transport, industry and residential combustion. The interaction terms between different sources obtained from a factor decomposition analysis were used as indicators of non-linear PM10 concentration responses to individual source emission reductions. Moreover, such interaction terms were analysed in light of the free ammonia / total nitrate gas ratio to determine the relationships between the chemical regime and the non-linearity at selected sites. The impacts of the different sources were not proportional to the emission reductions, and such non-linearity was most relevant for 100 % emission reduction levels compared with smaller reduction levels (50 % and 20 %). Such differences between emission reduction levels were connected to the extent to which they modify the chemical regime in the base case. Non-linearity was mainly associated with agriculture and the interaction of this source with road transport and, to a lesser extent, with industry. Actually, the mass concentrations of PM10 allocated to agriculture by the TS and BF approaches were significantly different when a 100 % emission reduction was applied. However, in many situations the non-linearity in PM10 annual average source allocation was negligible, and the TS and BF approaches provided comparable results. PM mass concentrations attributed to the same sources by TS and BF were highly comparable in terms of spatial patterns and quantification of the source allocation for industry, transport and residential combustion. The conclusions obtained in this study for PM10 are also applicable to PM2.5

Chemical mass balance of size-segregated atmospheric aerosol in an urban area of the Po Valley, Italy

International audienceA complete size segregated chemical characterisation was carried out for aerosol samples collected in the urban area of Bologna over a period of one year, using five-stage low pressure Berner impactors. An original dual-substrate technique was adopted to obtain samples suitable for a complete chemical characterisation. Total mass, inorganic, and organic components were analysed as a function of size, and a detailed characterisation of the water soluble organic compounds was also performed by means of a previously developed methodology, based on HPLC separation of organic compounds according to their acid character and functional group analysis by Proton Nuclear Magnetic Resonance. Chemical mass closure of the collected samples was reached to within a few percent on average in the submicron aerosol range, while a higher unknown fraction in the coarse aerosol range was attributed to soil-derived species not analysed in this experiment. Comparison of the functional group analysis results with model results simulating water soluble organic compound production by gas-to-particle conversion of anthropogenic VOCs showed that this pathway provides a minor contribution to the organic composition of the aerosol samples in the urban area of Bologna

Mass closure on the chemical species in size-segregated atmospheric aerosol collected in an urban area of the Po Valley, Italy

International audienceA complete size segregated chemical characterisation was carried out for aerosol samples collected in the urban area of Bologna over a period of one year, using five-stage low pressure Berner impactors. An original dual-substrate technique was adopted to obtain samples suitable for a complete chemical characterisation. Total mass, inorganic, and organic components were analysed as a function of size, and a detailed characterisation of the water soluble organic compounds was also performed by means of a previously developed methodology, based on HPLC separation of organic compounds according to their acid character and functional group analysis by Proton Nuclear Magnetic Resonance. Chemical mass closure of the collected samples was reached to within a few percent on average in the submicron aerosol range, while a higher unknown fraction in the coarse aerosol range was attributed to soil-derived species not analysed in this experiment. Comparison of the functional group analysis results with model results simulating water soluble organic compound production by gas-to-particle conversion of anthropogenic VOCs showed that this pathway provides a minor contribution to the organic composition of the aerosol samples in the urban area of Bologna