People spend one third of their life sleeping, but the bedroom, as a specific micro-environment, is often neglected when assessing human exposure to air pollutants. However, exposure during sleep may be significant in the long-term to the integrated individual exposure. This study aimed to assess the exposure during sleep, focusing on a multi-pollutant approach (comfort parameters, carbon dioxide – CO2, carbon monoxide – CO, formaldehyde (CH2O), total volatile organic compounds (VOCs), particulate matter – PM2.5 and PM10 – and ultrafine particles, particle number concentrations – PNC - and lung deposited surface area - LDSA). For that, the air quality during sleep (in real conditions) was monitored using real-time devices in 12 bedrooms of urban (Lisbon and Vila Franca de Xira) and rural (Ponte de Sor) areas of Portugal for one night. Volunteers were smokers and non-smokers. Considering the Portuguese legislation for indoor air quality (IAQ), 67% of the bedrooms registered CO2 levels above the limit value, while CH2O, VOC, PM10 and PM2.5 thresholds were exceeded in 30, 100, 36, and 45% of cases, respectively. Regarding ultrafine parameters, LDSA and PNC ranged from 7.3 to 95.2 μm2/cm3 and from 0.6 to 4.8 × 103/cm3, respectively. Even with no smoking indoors, smokers' bedrooms were found to have significant higher levels of CO, CH2O, PM2.5, PM10 and LDSA than non-smokers’ bedrooms, showing the effect of thirdhand smoke, exhalation of pollutants after smoking and infiltration on the degradation of the air quality in the bedroom. A recent new model of real-time monitor was also used for a wide set of IAQ parameters. Its performance to measure PM2.5 and CO2 was assessed, showing its applicability in real conditions. Although often neglected, these micro-environments should be considered in the integrated individual exposure to air pollutants and further studied. Main findings of the workSeveral pollutants (CO2, PM, VOCs and CH2O) exceeded the guidelines during sleep; smokers are exposed to higher levels of CO, CH2O, PM, and LDSA than non-smokers while sleeping.