We wanted to asses relations between the daily occurrence of asthma sy
mptoms and fluctuations of air pollution concentrations and meteorolog
ical conditions.In a panel of 31 asthmatic patients residing in the to
wn of Pitea in northern Sweden, severe symptoms of shortness of breath
, wheeze, cough and phlegm were recorded in an asthma diary together w
ith suspected causes. Sulphur dioxide, nitrogen dioxide, black smoke,
relative humidity and temperature were used to evaluate the relationsh
ip to the environment. By using multivariate analyses, we found that d
aily variations in the particulate pollution levels indicated by black
smoke levels below the criteria limits, had significant effects on th
e risk of developing severe symptoms of shortness of breath. This asso
ciation was stronger among 10 subjects, who had at least five incident
days with severe shortness of breath. Meteorological conditions were
not significant in the multivariate models. Cough and phlegm did not s
how significant relationships to any environmental condition that was
evaluated. Only one-third of the subjects reported, at least once duri
ng the study, symptoms believed to be related to air pollutants, altho
ugh we found significant correlations between the pollution levels and
the frequency of pollution-related symptoms. We conclude that an asso
ciation has been established for black smoke as pollutant and shortnes
s of breath as respiratory symptom, and that in certain asthmatics, ef
fects were occuring at lower particulate levels than suggested previou
sly.