3.1.1 Changes in Environmental Exposure
National lockdowns aimed to limit social interactions. In parallel, restraining the population indoors decreased exposure to environmental stressors such as respiratory infections, airborne allergens, particulate matter (PM10, PM2.5) and other air pollutants.17,18 These stressors are well-established inducers of airway inflammation, asthma exacerbations and worsening disease control.19-22 Consistent reports from across different countries documented decreased physical activity of children during lockdowns and increased time spent in front of screens, as a result of the increased time spent indoors.23-25 One study, using wearable sensors, objectively measured time spent outdoors and levels of physical activity in asthmatic children before and during lockdown periods and also confirmed a marked reduction of both during lockdown.8
Besides decreased outdoor exposure, there was also a notable decrease in anthropogenic pollutants emissions during lockdowns as a result of the reduced traffic volume and economic activity, which reversed following the lifting of the restriction measures.26 Greenhouse gases, specifically nitrogen dioxide (NO2), carbon monoxide (CO) and emissions of PM10, PM2.5 were substantially decreased compared to previous years.26-28 NO2 reductions were consistently low compared to non-lockdown periods across European countries, while levels of PMs were reduced but at different levels, possibly due to their source variability, such as the natural origin particulate matter from environmental dusts.29 Few studies showed no significant decreases in area-specific PM2.5, PM10, NO2 and ground-level ozone, despite reporting dramatic reductions in vehicular traffic, implying that possible reductions in pollutants were not adequately measured.13