C. Kirby et al., Reliability of nitrogen dioxide passive diffusion tubes for ambient measurement: in situ properties of the triethanolamine absorbent, J ENVIR MON, 2(4), 2000, pp. 307-312
Factors concerning NO2 uptake by the absorbent triethanolamine (TEA) in NO2
diffusion tubes are examined. Although the nominal freezing point of TEA i
s 17.9-21.2 degrees C, we show that, for a range of aqueous TEA solutions (
0-20% H2O), no freezing occurs even at -10 degrees C. Therefore NO2 collect
ion efficiency is unlikely to be impaired by low temperature exposure. The
recovery of TEA from the meshes of exposed samplers is determined as simila
r to 98%, even after 42 days, showing that the stability in situ of TEA is
unaffected by long-term exposure. A model of a diffusion tube sampling arra
y for simultaneous exposures, with a 0.1 m sampler spacing, shows that NO2
uptake by individual samplers is not affected by the presence of neighbouri
ng tubes in the array. This is confirmed by sampler precision at two Cambri
dge sites. Four sampler preparation methods are compared for differences in
NO2 uptake of exposed samplers. All methods employ TEA as absorbent, trans
ferred by either dipping meshes in a TEA-acetone solution or pipetting aliq
uots of a TEA-H2O solution onto the meshes. For samplers prepared by three
of the methods, no difference in NO2 uptake is found, but for samplers prep
ared using a 50% v/v TEA-H2O solution, a mean reduction of 18% is found. St
udent's t-tests show that the difference is highly significant (P less than
or equal to 0.001). Reasons for the difference are discussed.