There was occasionally an increase of PM concentrations at the
end of the afternoon, which was kept even after the end of classroom
occupancy, mainly due to cleaning activities. Fromme et al.
(2005) also reported that cleaning activities could contribute to
the increase of PM in the indoor air. To minimize this contribution,
cleaning activities in nurseries should be performed when children
go home and with high ventilation rates to outdoor.
The PM concentrations found in all the studied nurseries were
high, often above WHO guidelines, which is concerning, especially
for the finer fractions. Those were often found in the classrooms of
older children (4e5 years old). These have greater freedom and
ability to move when compared with younger ones, which is reflected
in their usual daily activities on nurseries increasing PM
concentrations in indoor air, as reported by Fromme et al. (2005).
Lunch rooms also exceeded WHO guidelines, especially in N_URB2
and N_URB3, mainly due to cooking activities and children movements.
Of concern were also the exceedances in 50% of the measurement
days to WHO PM2.5 guideline in N_URB2 classroom 1,
which is a baby nursery, and these younger children are most
vulnerable to adverse health effects of PM suspended in the air.