In epidemiological studies of an exposure-response association, often only a mismeasured exposure is taken on each individual of the population under study. If ignored, exposure measurement error can bias the estimated exposure-response association in question. A reliability study may be carried out to estimate the relation between the mismeasured and true exposure, which could then be used to adjust for measurement error in the attenuated exposure-response relationship. However, taking repeated exposure measurements may be expensive. Given a fixed total study cost, a two-stage design may be a more efficient approach for regression parameter estimation compared to the traditional single-stage design since, in the second-stage, repeated measurement is restricted to a sample of first-stage subjects. Sampling the extremes of the first-stage exposure distribution has been shown to be more efficient than random sampling.

The overall aim of this thesis was to validate diffusive samplers for measurements of nitrogen dioxide (NO2) and nitrogen oxides (NOx). The Willems badge was validated for NO2 measurements both in laboratory tests and in field tests (Paper I-II). The sampling rate was 40.0 mL/min for ambient air concentrations and 46.0 mL/min for higher concentrations. No effects of different factors on sampling rate were found except for a reduced sampling rate at low wind velocity. The results of the laboratory validation were confirmed in field tests in ambient air and with personal sampling. The correlation between diffusive samplers and the reference monitor was good for ambient measurements. In conclusion, the Willems badge performs well at wind velocities down to 0.3 m/s, and this makes it suitable for personal sampling but less suitable for measurements in indoor air where the wind velocity is lower. Paper III reports about the field validation of the Ogawa diffusive samplers. Absolute humidity and temperature were found to have the strongest effect on sampling rate with lower uptake rates at low absolute humidity or temperature. The sampling rates above 0 °C were 8.6 mL/min for NO2 and 9.9 mL/min for NOx. NO2 and NOx concentrations that were determined using the manufacturer’s protocol were either underestimated or overestimated. The agreement between concentrations measured by the Ogawa sampler and the reference monitor was improved when field-determined sampling rates were used to calculate concentrations. Paper IV is based on a study with the aim of assessing the exposure of the Swedish general population to NO2 and some carcinogenic substances. The surveys were performed in one of five Swedish cities every year. In each survey, personal measurements of NO2 and some carcinogenic substances were conducted on 40 randomly selected individuals. In the study presented in this thesis, the NO2 part of the study is in focus and results were available for eight surveys conducted across the five cities. The estimated arithmetic mean concentration for the general Swedish population was 14.1 μg/m3. The exposure level for NO2 was higher for smokers compared with non-smokers, and the NO2 exposure levels were higher for people who had gas stoves at home or who were exposed at their workplace. The exposure was lower for those who had oil heating in their houses.

Outside to the wide range of potential benefits, the use of nanomaterials can endanger human health and the environment. This diploma thesis presents the results of pilot measurements, where the exposure of nanoparticles was monitored. Based on a literature research a suitable method for measurement was the three-stage OECD model. Based on this model, measurements were performed in three welding workplaces, where nanoparticles are produced incidentally. The measurement consisted of collecting information and measuring the concentration of nanoparticles in the workplace, where data collection was focused only on inhalation exposure. During welding, 0.3 m size particles are produced and their concentration is strongly influenced by the welding material, type of welding and suction. The particles are amorphous in terms of morphology and contain manganese, iron and silicon, which can cause neurodegenerative diseases. Furthermore, the results indicate the importance of monitoring oral exposure.

This thesis deals with methological issues in the study of chemical exposure and sick building syndrome (SBS). SBS is a combination of general, mucosal and skin symptoms that some people experience when staying in specific buildings. The aim was to find chemical patterns associated with SBS, but also to address methological problems in such study. The plan was to conduct a case-control study comparing the two groups’ chemical exposure, where cases were defined as those having at least one general, one mucosal and one skin symptom each week the last three months. For the planning it was necessary to know if cases and controls could be selected from the same building. If everyone in a building have the same chemical exposure it is no use to compare exposure between two persons at the same workplace. In the first paper exposure to more than 100 compounds is compared between 79 participants working in eight buildings. It was found that for the majority of compounds the variation in exposure was larger within buildings than between buildings, which means that cases and controls could be allowed to work in the same building. The second paper is a comparison of three adsorbents usability in finding differences in chemical exposure between SBS cases and controls. This was done by using chemometrical methods but comparisons of sampled amounts, blank values and reproducibility were also done. Tenax TA was found to be the best adsorbent, hence used in the case-control study. In recent years ozone and ozone reaction products with unsaturated volatile organic compounds (VOCs) has been in focus. Nitrogen dioxide is another gas affecting oxidation of reactive VOCs. Formaldehyde is an irritant formed when unsaturated VOCs are oxidised, and in some studies a relation with SBS has been found. In paper three the relation between personal exposure to formaldehyde, nitrogen dioxide, ozone, terpenes and SBS has been investigated among more than 200 office workers in a case control study in Umeå and Vasa. Cases (based on symptoms during the week of measurements) had lower ozone exposure than controls. No further associations were found at present exposure levels. A planed analysis of relations to VOCs could not be done due to analytical problems, and problems due to difficulties with consistent identification of compounds in a very large data set. These problems are further discussed in the thesis. In the case-control, study participants answered questionnaires about symptoms during "the past three months", "right now" (when answering the questionnaire), and during the week of exposure measurements. In the fourth paper the stability of symptoms were compared by answers at different occasions. It was found that the case/control concept was as stable as individual symptoms. More participants with atopic disease and those 41 years old or younger changed class compared with those without atopic disease and older participants. Measurement activities appeared to make participants report more symptoms. Fatigue, dry eyes and dry skin are suggested to be symptoms with strongest, and illness/dizziness to be weakest association with IAQ. / KLUCK-projektet

Diss. (sammanfattning) Umeå : Umeå universitet, 2010. / Härtill 4 uppsatser.