| dc.description.abstract | The aim of the present thesis was to study the carbonaceous fraction of ambient aerosols in the Norwegian environment, with a particular focus on the water-soluble carbonaceous fraction. Studies were based on bulk and molecular analysis of the carbonaceous material, where the molecular approach was based on novel high-performance liquid chromatography/highresolution mass spectrometry time-of-flight (HPLC/HRMS-TOF) methodology developed as a part of the work of the work presented in the thesis. In the following the main findings are summarized.
I.
The study demonstrated that carbonaceous material was the major fraction of the ambient aerosol mass in the environments investigated, accounting for 46-83% of PM10. It was shown that parts of the population, living outside the major urban areas, could be exposed to equal (PM10) and even higher (PM2.5) concentrations of combustion derived particulate organic carbon than those living in major cities due to the impact of local sources, such as residential wood burning. Emissions from residential wood burning had a profound influence on the seasonal variation of the carbonaceous material, being 3.5 times higher during winter compared to summer at the suburban site investigated. The impact of vehicular traffic had a substantial influence on the concentrations of elemental carbon (EC). EC concentrations were up to one order of magnitude higher in the urban areas compared to the suburban area. The relative importance of water-insoluble organic carbon (WINSOC) and water-soluble organic carbon was typically dependent on the prevailing source. WINSOC, along with EC, was most abundant in areas dominated by emissions from vehicular traffic, whereas WSOC dominated in areas where residential wood burning was the prevailing source. The positive sampling artefact of organic carbon (OC) was substantial at all the sit investigated, ranging from 9 – 42%. The results indicate that water-soluble organic carbon may account for the major part of the positive artefact. Comparing the performance of the two approaches applied, the quarts-behind-Teflon approach provided a more than twofold higher estimate (42%) of the positive artefact than the quartz-behind-quartz approach (18%). Converting the positive artefact of OC into organic material, 5.3-26% of PM10 could be attributed to vaporous organic material. Failing to account for this artefact could lead to a gross overestimation of the particulate organic carbon, as well as the ambient aerosols mass.
II.
A novel high-performance liquid chromatography/high-resolution mass spectrometry time-offlight (HPLC/HRMS-TOF) method for determination of the monosaccharide anhydrides (MAs) in ambient aerosols was developed. The method offers a new and valuable analytical approach for studies using MAs as tracers for biomass burning, and is less labouring and less time consuming than the currently applied methodology. In addition, this method will increase the diversity of chemical methods available for analysis of MAs, which is important for validation purposes. Finally, HPLC/HRMS and GC/MS are complementary methods, implying that there is a potential to extend the knowledge of the organic aerosol composition.
III.
Monosaccharide anhydrides (MAs), and in particular levoglucosan, were abundant in the environments investigated, emphasizing the importance of wood burning for residential heating as a source of ambient aerosols. Concentrations of levoglucosan in the range 10-1000 ng m-3 were reported. The mean concentration of levoglucosan accounted for 2.4% of the PM10 mass concentration at the suburban site investigated. The MAs were exclusively associated with fine aerosols, and exhibited a unimodal size distribution characterized by a mode with a maximum at 561 nm. It was demonstrated that the temporal variation of levoglucosan partly is a function of the ambient temperature. Based on levoglucosan measurements, 24% of the PM10 mass concentration at the urban site investigated was attributed to emissions from wood burning. Using the AirQUIS dispersion model the corresponding percentage was 50%. The difference was partly attributed to the rather high emission factor used in the AirQUIS model, which seems to be based on an insufficiently documented assumption of a low burn rate characteristic for Norwegian conditions.
IV.
The presence of sugars and sugar-alcohols in ambient aerosols were documented in all environments investigated, confirming the ubiquity of primary biological aerosol particles (PBAP). The mean concentration of the sum of the four sugars and the three sugar-alcohols ranged between 21 - 285 ng m-3 in PM10 at the sites assessed. However, daily concentrations exceeding 500 ng m-3 were observed. A seasonal pattern was observed for both sugars and sugar-alcohols, both having peak concentrations during summer and fall. In areas heavily influenced by residential wood burning during winter, the mean concentration of individual sugars was found to equal the concentrations reported during summer. Sugars and sugar-alcohols were mainly associated with coarse aerosols, but sugars in the fine mode were found to make a substantial contribution during winter, spring and early summer. It is argued that ruptured pollen may be a significant source of sugars in the fine aerosol. Moreover, in areas influenced by residential wood burning, sugars and sugar-alcohols were predominantly associated with fine aerosols. High levels of highly sugar containing honeydew were found to be deposited on the leaves and on the ground underneath the canopy of threes. However, it remains to study to what extent this is entrained into the atmosphere, and if so, what are their size distribution | nb_NO |
