The influence of traffic and wood combustion on the stable isotopic composition of carbon monoxide

Carbon monoxide in the atmosphere is originating from various combustion and oxidation processes. Recently, the proportion of CO resulting from the combustion of wood for domestic heating may have increased due to political measures promoting this renewable energy source. Here, we used the stable isotope composition of CO (δ<sup>13</sup>C and δ<sup>18</sup>O) for the characterization of different CO sources in Switzerland, along with other indicators for traffic and wood combustion (NO<sub>x</sub>-concentration, aerosol light absorption at different wavelengths). We assessed diurnal variations of the isotopic composition of CO at 3 sites during winter: a village site dominated by domestic heating, a site close to a motorway and a rural site. The isotope ratios of wood combustion emissions were studied at a test facility, indicating significantly lower δ<sup>18</sup>O of CO from wood combustion compared to traffic emissions. At the village and the motorway site, we observed very pronounced diurnal δ<sup>18</sup>O-variations of CO with an amplitude of up to 8‰. Solving the isotope mass balance equation for three distinct sources (wood combustion, traffic, clean background air) resulted in diurnal patterns consistent with other indicators for wood burning and traffic. The average night-time contribution of wood-burning to total CO was 70% at the village site, 49% at the motorway site and 29% at the rural site based on the isotope mass balance. The results, however, depend strongly on the pure source isotope values, which are not very well known. We therefore additionally applied a combined CO/NO<sub>x</sub>-isotope model for verification. Here, we separated the CO emissions into different sources based on distinct CO/NO<sub>x</sub> emissions ratios for wood combustion and traffic, and inserted this information in the isotope mass balance equation. Accordingly, a highly significant agreement between measured and calculated δ<sup>18</sup>O-values of CO was found (<i>r</i>=0.67, <i>p</i><0.001). While different proxies for wood combustion all have their uncertainties, our results indicate that the oxygen isotope ratio of CO (but not the carbon isotope ratio) is an independent sensitive tool for source attribution studies

Lidar- und Sonnenphotometermessungen von Saharastaubschichten über dem Atlantik

Ein einzigartiger Datensatz an Lidarmessungen von Saharastaubschichten, die in den letzten Jahren auf Fahrten des Forschungsschiffes Polarstern durchgeführt wurden, konnte für den Bereich des tropischen und subtropischen Atlantiks gewonnen werden. Die Messungen mit dem mobilen Aerosol Raman Lidar (MARL) des AWI lieferten Profile des Rückstreukoeffizienten und der Depolarisation bei zwei Wellenlängen (355 nm und 532 nm). In Höhen von ca. 2 bis 6 km wurden mit diesem Instrument Aerosole beobachtet, die aufgrund ihrer optischen Eigenschaften als Staubschichten identifiziert wurden. Rückwärtstrajektorien bestätigen die nordafrikanische Herkunft der entsprechenden Luftmassen und lassen keinen Zweifel, dass es sich um Saharastaub handelte. Die optische Dicke der Schicht lag meist im Bereich von 0.1 bis 0.3, aber auch Werte bis zu 0.7 wurden erreicht, wie die durchgeführten Sonnenphotometermessungen zeigten. Mit einem neuen Verfahren, das auf der Mie-Theorie und nichtsphärischer Streurechnungen basiert, wurde der effektive Radius und der Brechungsindex der Staubpartikel aus den Lidardaten abgeleitet. Die Ergebnisse stimmen gut mit den Resultaten überein, die mit ähnlichen Verfahren aus Photometerdaten hergeleitet werden können

Comparison of several wood smoke markers and source apportionment methods for wood burning particulate mass

Residential wood combustion has only recently been recognized as a major contributor to air pollution in Switzerland and in other European countries. A source apportionment method using the aethalometer light absorption parameters was applied to five winter campaigns at three sites in Switzerland: a village with high wood combustion activity in winter, an urban background site and a highway site. The particulate mass from traffic (PMtraffic) and wood burning (PMwb) emissions obtained with this model compared fairly well with results from the 14C source apportionment method. PMwb from the model was also compared to well known wood smoke markers such as anhydrosugars (levoglucosan and mannosan) and fine mode potassium, as well as to a marker recently suggested from the Aerodyne aerosol mass spectrometer (mass fragment m/z 60). Additionally the anhydrosugars were compared to the 14C results and were shown to be comparable to literature values from wood burning emission studies using different types of wood (hardwood, softwood). The levoglucosan to PMwb ratios varied much more strongly between the different campaigns (4–13%) compared to mannosan to PMwb with a range of 1–1.5%. Possible uncertainty aspects for the various methods and markers are discussed

Assessing urban air quality through measurements and modelling and its implications for human exposure assessment

Outdoor air pollution is a major contributor to adverse health effects of citizens, in particular those living in urban environments. Air quality monitoring networks are set up to measure air quality in different environments in compliance with national and European legislation. Generally, only a few fixed monitoring sites are located within a city and thus cannot represent air pollutant concentrations in urban areas accurately enough to allow for a detailed human exposure assessment. Other approaches to derive detailed urban air pollutant concentration estimates exist, such as dispersion models and land-use regression (LUR) models. Low-cost portable air quality monitors are also emerging, which have the potential to add value to existing monitoring networks by providing measurements at greater spatial resolution and also to provide individual-level exposure assessment. The aim of this thesis is to demonstrate how measurements and modelling in combination allow detailed investigations of the variability of air pollutants in space and time in urban area, and in turn improve on the current exposure assessment methods. Three types of low-cost portable monitors measuring NO2, O3 (Aeroqual monitors) and PM2.5 (microPEM monitor) were evaluated against their respective reference instruments. The Aeroqual O3 monitor showed very good correlation (r2 > 0.9) with the respective reference instruments, but biases in the slope and intercept coefficients indicated that calibration of Aeroqual O3 monitor was needed. The Aeroqual NO2 monitor was subject to cross-sensitivity from O3, which, as demonstrated, can be effectively corrected by making O3 and NO2 measurements in tandem. Correlation between the microPEM monitor and its reference instrument was poor (r2 < 0.1) when PM2.5 concentrations were low ( 0.69) during periods with elevated PM2.5 concentrations. Relative humidity was not found to affect the raw results of PM2.5 measurements in a consistent manner. All three types of monitors cannot be used as equivalent or indicative methods instead of reference methods in studies that require quantification of absolute pollutant concentrations. However, the generally good correlations with reference instruments reassure their application in studies of relative trends of air pollution. Concentrations of PM2.5, ultrafine particles (UFP) and black carbon (BC) were quantified using portable monitors through a combination of mobile and static measurements in the city of Edinburgh, UK. The spatial variability of UFP and BC was large, of similar magnitude and about 3 times higher than the spatial variability of PM2.5. Elevated concentrations of UFP and BC were observed along streets with high traffic volumes whereas PM2.5 showed less variation between streets and a footpath without road traffic. Both BC and UFP significantly correlated with traffic counts, while no significant correlation between PM2.5 and traffic counts was observed. The relationships between UFP, NO2 and inorganic components of PM2.5 were further investigated through long-term measurements at roadside, urban background and rural sites. UFP moderately correlated with NOx (NO2 + NO) and showed varying relationships with NOx depending on the particle size distribution. Principal component analysis and air-mass back trajectory analysis revealed that PM2.5 concentrations were dominated by long-range transport of secondary inorganic aerosols, whereas UFP were mainly related to varying local emissions and meteorological conditions. These findings imply the need for different policies for managing human exposure to these different particle components: control of much BC and UFP appears to be manageable at local scale by restricting traffic emissions; however, abatement of PM2.5 requires a more strategic approach, in cooperation with other regions and countries on emissions control to curb long-range transport of PM2.5 precursors. A dispersion model (ADMS-Urban) was used to simulate high resolution NO2 and O3 concentrations in Edinburgh. The effects of different emission and meteorological input datasets on the resulting modelled NO2 concentrations were investigated. The modelled NO2 and O3 concentrations using the optimal model setup were validated against reference instrument and diffusion tube measurements. Temporal variability of NO2 was predicted well at locations that were not heavily influenced by local effects, such as road junctions and bus stops. Temporal variability of O3 was predicted better than for NO2. Long-term spatial variability of NO2 was found to correlate well with diffusion tube measurements, while modelled spatial variability of O3 in ADMS-Urban compared poorly with diffusion tube measurements. However, it was found that the O3 diffusion tube measurements may be subject to some unidentified biases affecting their accuracy. Land-use regression (LUR) models are widely used to estimate exposure to air pollution in urban areas. An appropriately sized and designed monitoring network is an important component for the development of a robust LUR model. Concentrations of NO2 were simulated by ADMS-Urban at ‘virtual’ monitoring sites in 54 different network designs of varying numbers and types of site, using a 25 km2 area including much of the Edinburgh city area. Separate LUR models were developed for each network. These LUR models were then used to estimate ambient NO2 concentrations at all residential addresses, which were evaluated against the ADMS-Urban modelled concentration at these addresses. The improvement in predictive capability of the LUR models was insignificant above ~30 monitoring sites, although more sites tended to yield more precise LUR models. Monitoring networks containing sites located within highly populated areas better estimated NO2 concentrations across all residential locations. LUR models constructed from networks containing more roadside sites better characterised the high end of residential NO2 concentrations but had increased errors when considering the whole range of concentrations. No particular composition of monitoring network resulted in good estimation simultaneously across all residential NO2 concentration and of the highest NO2 levels implying a lack of spatial contrast in LUR-modelled pollution surface compared with the dispersion model. Finally, the results from the measurement and modelling studies presented in thesis are synthesised in the context of current exposure assessment studies. Low-cost air-quality monitors currently do not possess and are unlikely in the near future to provide the robustness and accuracy to replace the existing routine monitoring network. Development of the low-cost air-quality should be aiming at upgrading them as the indicative method as defined in the data quality objective in the EU directive. The monitoring sites used to build LUR models should capture well the population distribution in the study area as opposed to capturing the greatest pollution contrast. The traditional methods of evaluating LUR models are also ineffective in characterising the models’ capability at estimating pollutant concentration at residential address. Given that the dispersion models are also subject to the availability and uncertainties in the input data, future air quality model development should endeavour to incorporate both dispersion and land-use regression models, where the uncertainty in the input data can be reduced by using LUR models built on actual measurements, and the limitation in the statistical modelling can be replaced by adopting the deterministic approach used in the dispersion model

Carbon in Particulate Matter in the air

Ugljik (lat. carbo) u elementarnom stanju pojavljuje se kao dijamant, grafit, fuleren i crni amorfni ugljik. Crni amorfni ugljik nalazi se i u lebdećim česticama u atmosferi, a glavni oblici su: elementarni (EC), organski (OC) i karbonatni (CC) ugljik. Atmosferske čestice ugljika emitiraju se iz više od 70 različitih vrsta izvora onečišćenja zraka. EC je primarni onečišćivač koji nastaje nepotpunim izgaranjem fosilnih i biljnih goriva, a pojavljuje se još i kao čestice čađe te ga nalazimo i u sedimentima, tlima i ledu. Mnoga kvantitativna određivanja EC temelje se na njegovoj kemijskoj inertnosti, termičkoj stabilnosti i optičkim svojstvima. Organski spojevi kao što su policiklički aromatski ugljikovodici (PAU), poliklorirani bifenili (PCB), poliklorirani dibenzo-p-dioksini i furani, polibromirani difenileteri te druga organska onečišćenja nastaju procesima izgaranja i stvaranja sekundarnih organskih aerosola, a ubrajaju se u organski ugljik (OC). Svrha je članka opisati različite oblike ugljika u lebdećim česticama u zraku, njihov negativni učinak na zdravlje ljudi, klimu i atmosferu te opisati metode za njihovo određivanje.Carbon (Latin carbo) in elemental form appears as diamond, graphite, fullerene, and black amorphous carbon. Black amorphous carbon can be found in atmospheric aerosols and its main forms are elemental (EC), organic (OC), and carbonate (CC) carbon. Atmospheric carbon particles are transmitted through more than 70 sources of air pollutants. Elemental carbon is the primary pollutant, which results from incomplete combustion of fossil and biomass fuels. It also appears as soot, in sediment, soil, and ice core. Many quantitative determinations of elemental carbon are based on its chemical inertness, thermal stability, and visual features. Organic carbon includes organic compounds such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), polychlorinated dibenzo–p-dioxins and furans, polybrominated diphenylethers, and other organic pollutants are the products of combustion and formation of secondary organic aerosols. The aim of this paper was to describe different forms of carbon in the atmosphere, how they affect people, climate, and the atmosphere, and to give an overview of different methods for their determination