Born in fire, borne by air : Source attribution and physicochemical characterization of ship and ambient aerosols in the Baltic region
Abstract: Aerosol emissions from anthropogenic activities cause detrimental health effects and affect the climate system. Combustion is a large source of airborne fine particulate matter (PM2.5) and the uncertainties of the climate role of these emissions are still large. A good understanding of the microphysical properties of aerosols from various sources and their atmospheric aging is essential for accurate assessment of the health and climate impact. It is also important to follow up legislative actions aimed at reducing emissions, with ambient observations. The overall aim of this thesis is to present results from field observations of aerosols from combustion sources, and contribute to the general knowledge on the particle concentrations and physicochemical properties in the Baltic region. Ship and traffic emissions were investigated in detail in several field campaigns in Sweden. Soot, or black carbon, was specifically measured with several different measurement techniques. Other aerosol components were also monitored, including gaseous species, organic matter, and sulfate, which is of specific interest in ship emission characterization. Additionally, source apportionment of the carbonaceous aerosol from a field campaign in northern Poland is presented, which adds to the knowledge about black carbon emissions in a polluted part of Europe. The absorbing equivalent black carbon emission factor (EFeBC) was measured for over 300 fresh ship plumes in a Port within a sulfur emission control area. EFeBC had decreased by 30 %, from 0.48±0.81 to 0.34±0.40 g(kg fuel)-1 between 2014 and 2015 after a reduction of fuel sulfur content. If such a reduction is expected as marine fuel quality is improved, this can have important implications also outside emission control areas, as a global sulfur cap is implemented. A more complete physicochemical characterization and simulated aging of ship plumes of an age between about 20 and 30 minutes was performed at a coastline, and the contribution of one shipping lane to local aerosol concentration was quantified. Novel methods to tie plumes to individual ships and to estimate contribution to coastal exposure were developed. Ships contributed as much as 10-18 % of ultrafine particles at the coast, but only about 1 % or less (40 ng m-3) to local PM. Non-refractory PM1 was mainly organics and sulfate (56 and 36 %, respectively), and the average eBC contribution was 3.5±1.7 ng m-3. The absorption Ångström exponent of the plume eBC was close to unity, indicating black (BC) rather than brown carbon (BrC). Oxidation flow reactor treatment of the aerosol was performed, resulting in occasionally strong increase in secondary aerosol mass.The ambient aerosol and its BC fraction was characterized in an urban and rural environment in southern Sweden, and the transport of the aerosol between these nearby sites was investigated. The conclusion was that there was 2.2-2.5 times higher BC mass and up to four times higher BC number concentration at the urban site. Additionally, the soot particles in the city were slightly smaller and less coated. The influence of an urban plume at the rural site was possible to detect and quantify during specific meteorological conditions. The regional background dominated the total aerosol contribution, and was largely due to southeastern air masses.A quantification of particle sources in Polish air is lacking. Winter field campaign data from northeastern Poland showed that domestic coal combustion, domestic wood combustion and traffic contributed 41, 21, and 38 % respectively to carbonaceous particulate matter. The three sources were separated using a combination of apportionment methods based on aerosol absorption properties and chemical markers.Generally, the eBC concentrations were approximately twice as high in Poland as in Sweden, and twice as high in a Swedish city compared to a rural background site. Emissions from a large shipping lane were not a large source of eBC at the coastal sampling site. However, despite the relatively good air quality in Sweden, air pollution is still above the environmental quality objectives, and of importance to health locally, and climate in general.
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