Introduction: Particulate matter, nitrogen dioxide (NO2) and ozone are recognized as the three pollutants that most significantly affect human health. Asthma is a multifactorial disease. However, the place of residence has rarely been investigated. We compared the impact of air pollution, measured near patients' homes, on emergency department (ED) visits for asthma or trauma (controls) within the Provence-Alpes Cote-d'Azur region. Methods: Variables were selected using classification and regression trees on asthmatic and control population, 3-99 years, visiting ED from January 1 to December 31, 2013. Then in a nested case control study, randomization was based on the day of ED visit and on defined age groups. Pollution, meteorological, pollens and viral data measured that day were linked to the patient's ZIP code. Results: A total of 794,884 visits were reported including 6250 for asthma and 278,192 for trauma. Factors associated with an excess risk of emergency visit for asthma included short-term exposure to NO2, female gender, high viral load and a combination of low temperature and high humidity. Conclusion: Short-term exposures to high NO2 concentrations, as assessed close to the homes of the patients, were significantly associated with asthma-related ED visits in children and adults. (c) 2017 Elsevier Ltd. All rights reserved.