Characterization of Aerosols Related to Occupational and Public Environments as Applied to Isocyanates and Road Wear

Abstract: The aim of this thesis was to characterize a personal denuder/filter sampler for isocyanate aerosol and to study the emission of airborne particles from the interaction between studded tires and pavements. Both types of aerosols are highly relevant for health studies in public and occupational environments. The adverse health effects of airborne isocyanate exposure are well known in the occupational environment as a frequent cause for work related asthma and effects can be induced at very low concentrations. The health effects of airborne particles from road wear are less investigated, but several reports suggest that inhaled particles of non specific origin significantly reduce the general public health condition and as the wear of the pavement caused by studded tires is a major particle source in countries where these types of tires are used the adverse heath effects may be considerable. It is important to reduce the wear on pavement in order not to exceed limit values of airborne particle concentration. The instrumental equipments used in these studies were Scanning Mobility Particle Sizer (SMPS), Aerodynamic Particle Sizer (APS) and particle conditioning with Volatility Tandem Differential Mobility Analyzer (VTDMA). The measurements on road dust were conducted on a road simulator which consists of four wheels running on a six meter in diameter circular track. The results from the isocyanate sampler shows that due to the phase equilibrium between gas and condensed phase the analyte may evaporate during the passage through the denuder and thus shift the analyzed gas/condensed ratio towards the gas fraction. In the road dust study a mode of particle originating from the tire rubber was detected. The mean diameter of the particles in this mode was 25-50 nm depending on type of tire. The source strength of this emission was calculated to about 1012 particles per kilometer. The mass concentration of particles less than 10 µm in the test hall were dependent upon the type of pavement used. The more wear resistant quartzite based pavement led to a 3-4 times lower particle mass level than the less durable granite based pavement. The results from the personal sampler study can be used to better interpret measuring results from phase fractionated isocyanate sampling. The number emission rate of the nanometer sized particles from the tires is a hundred fold lower than the emission from the exhaust of a diesel car. The study on wear particles from the wear by studded tires have proven that the road simulator is a valuable tool for estimating the effects of different emission reducing methods such as legal regulation of tires and choice of pavement.