Background: This study examines the possible effect of exposure to aerosols and gases on lung function in a fertilizer plant in Norway. Methods: Dynamic lung volumes (FVC and FEV1) of 383 workers were measured in 2007 and 2010. During the follow-up period, most workers performed tasks with low exposure levels of acid aerosols and inorganic gases. The overall median inhalable and thoracic aerosol exposure levels were 1·1 and 0·21 mg/m3, respectively. A questionnaire on respiratory symptoms was provided. Results: During the follow-up period, there was an adjusted decrease of FEV1 of 18 ml/year (P<0·001). The respiratory symptoms score was low during follow-up. Conclusions: Work in this fertilizer industry may lead to an excessive lung function decline. We have, however, not been able to find any plausible exposure related explanation for the overall lung function decline.