Abstract
The collection efficiency of HCl vapour on nylon filters, and potential interferences from partial collection of other chlorinated gases, has been assessed by generating test atmospheres containing known concentrations of the gases of interest. HCl collection efficiency was generally better than 80% for all conditions of humidity (10–80% r.h.), flow rate (0.6–6 ℓ min
−1) and temperature (18–24°C) for normal rural ambient air sample loadings of < 100 μg HCl. At higher loadings, and at all concentrations with the addition of high loadings of HNO
3, pronounced breakthrough of Cl
− was observed and efficiency declined to as little as 10%. Chlorine gas (C1
2) was retained with 61–75% efficiency, and CH
3Cl could potentially account for up to 20% of Cl
− collected at low HCl levels. CH
3CC1
3, CH
2ClCH
2Cl, CCl
4 and CH
2Cl
2 are collected only with a very low efficiency.
Atmospheric samples collected at urban and rural sites in south-east England showed HCl levels of between 0.12 and 1.49 μ m
−3. Hydrochloric acid was a significant contributor to total atmospheric acidity, greater than HNO
3 on an equivalence basis. During episodes of relatively clean air it exceeded aerosol SO
4
2− acidity.