Lung cancer incidence is increased in urban areas including Stockholm. Although smoking is the most important risk factor for lung cancer, it does not seem to fully explain the excess risk and ambient air pollution may be of importance.

A simulation project was started called the LUCAS project, a retrospective study of LUng CAncer in Stockholm county. The SLB·analys part of the study is to perform simulations of the exposure of sulphur dioxide and nitrogen oxides to persons who have died in lung cancer. In April 1997 SLB·analys finished the building of emission databases for the sixties, seventies and eighties and the simulations from these databases.

Methods

1000 cases of lung cancer in men aged 40 to 75 diagnosed between 1985 and 1990 were identified in the regional cancer registry. 3000 controls were selected from the general population. Information on individual exposure was collected with a postal questionnaire, including questions on dwellings from 1950 and onwards. The addresses were then transformed into geographical coordinates using the MAPINFO computer software in conjunction with a regional geographical database.

It was possible to assign geographical coordinates automatically for most of the addresses stated in the questionnaires. The address coordinates for the remaining addresses were assigned semi-automatically using graphical computer maps. The validity of the geographical coordinates was assessed by a visual graphical method and by comparison with another GIS method of assigning coordinates.

Very detailed regional emission databases for 1993 were used as starting databases. The growing of the urban areas in the Stockholm region, the expansion of the district heating system and the growth in the road traffic were then mapped through the sixties, seventies and eighties.

Emission databases were built for the sixties,seventies and eighties, describing SO2 and NOx emissions from the main sources - heating and road traffic. The emission databases were built by using the AIRVIRO system. The databases describe the average emissions during the sixties, seventies and eighties. The emissions are described as point sources, grid sources and line sources.

Dispersion calculations from the emission databases representing the sixties, seventies and eighties were performed by use of the Gaussian model in the AIRVIRO system. Calculations were made for SO2 and NOx as yearly mean values. The NOx concentrations were then also transformed to NO2 data using relationships from the measurement databases. The dispersion calculations were performed in four different resolutions - 2000x2000, 500x500, 200x200 and 100m times 100m calculation grids.

The results from the dispersion calculations were compared with measured data from the sixties, seventies and eighties for SO2, and measured data from the eighties for NOx and NO2. Emission levels were the most uncertain input data to the calculations. By an iteration of emission and dispersion calculations the differences between calculated and measured data could be minimized. After the final dispersion calculations all calculated data at monitoring stations are in an interval plus minus twenty percent compared to measured data.

NOx and NO2 were used as indicators of air pollution from road traffic in the study. Therefore the final dispersion calculations included only these sources. For main streets in the city centre the street canyon contribution of NOx and NO2 concentrations were added to the roof concentrations. These contributions were defined by dispersing calculations with the AIRVIRO street canyon model. The SO2 concentration fields were used as indicators for air pollution from heating.

The air pollution data were then linked to 11000 individual address coordinates for the relevant time intervals yielding exposure indices for each of the three air pollution indicators for each decade.