Exposure to total particulate matter from urban air pollution (UP) or biomass burning (BP) has been associated with lung impairment. We investigated the time-dependency of lung functional recovery in BALB/c mice exposed to UP or BP particles. During 4 weeks they weekly received 3 nose-only instillations of 15 μL of distilled water (C) or UP or BP (15 μg/15 μL saline). Mice were weighed weekly. 1 (C1, UP1, BP1), 2 (C2, UP2, BP2), 7 (C7, UP7, BP7) or 14 (C14, UP14, BP14) days after the last instillation, pulmonary mechanics, FRC and histology were measured; catalase and superoxide dismutase activities were evaluated in lung homogenates. Body mass gain was similar among the groups. Pulmonary elastance and its viscoelastic component (cmH2O/mL), resistive and viscoelastic pressures (cmH2O) were higher in UP1 (31.1±1.6, 7.2±0.3, 0.8±0.04; 1.5±0.1, respectively) and BP1 (31.0±0.4, 6.6±0.3, 0.8±0.04, 1.4±0.1) than in C1 (23.5±1.6, 4.3±0.1, 0.6±0.04, 0.8±0.1, respectively). These parameters returned to control values at day 2, except for resistive pressure that normalized at 7 days. Alveolar collapse (%) was larger in UP1 (21.8±5.9) and BP1 (23.2±1.9) than in C1 (1.7±0.3) and returned to baseline at 7 days, while bronchoconstriction index and alveolar and bronchial lesion scores increased in UP1 (2.3±0.2, 3.0±0.3 and 2.3±0.4, respectively) and BP1 (2.3±0.2, 2.8±0.3 and 2.3±0.4, respectively) in relation to C1 (1.5±0.2, 1.0±0.3 and 0.8±0.4, respectively) and normalized in 2 days. No differences were found in FRC and oxidative stress. Thus, a 4-week exposure to UP and BP induced lung impairment that resolved 7 days after the last exposure. Supported by: FAPERJ, CNPq, MCT.