Environmental Engineering Reference
In-Depth Information
Relationship between indoor radon concentrations and outdoor temper-
atures (indoor/outdoor temperature differences). (From Kunz, Z.,
Figure 2.9
Proc. 4th Internatl.
Conf. Indoor Air Qual. Climate
, Berlin, 414, 1987.)
rological factors, the height and volume of the building, and operation of
mechanical exhaust systems.
Radon transport is significantly enhanced when buildings are under
significant negative pressure, particularly at floor level. In moderate to colder
climates, most dwellings experience what is described as the “stack effect”
(see Chapter 11). Indoor/outdoor temperature differences cause residential
buildings to be under positive pressure near the roof and negative pressure
near the floor. This phenomenon causes outdoor air to flow in at the base
and out at the ceiling. The effect of temperature differences (responsible for
the stack effect) on indoor radon levels can be seen in
Figure 2.9
.
Note the
strong diurnal variation in outdoor temperature and the corresponding vari-
ation in indoor radon concentration. Radon levels are at a maximum during
the coolest part of the day when pressure differentials are greatest.
Meteorological variables such as outdoor temperature are not alone in
affecting indoor radon concentration. Pressure-driven flows are also influ-
enced by both the wind speed and direction. During moderate to high winds,
the windward side of a building will be under positive pressure and the
leeward side under high negative pressure. Indoor radon levels will be lower
on the windward side and higher on the leeward side.
Other meteorological variables reportedly affect indoor radon levels.
Drought conditions can cause cracks in otherwise impermeable clay soils,
channeling radon upward from deeper soils and geological strata. Dry soil
conditions also increase the volume of soil pores available for radon accu-
