Influence of meteorological factors on the NO2 measurements by passive diffusion tube

Abstract

Abstract This paper describes the results of experiments in exposure chamber to determine the effects of wind velocity, temperature and relative humidity on the performances of Palmes tube, for measuring nitrogen dioxide in the outdoor environments. A total of 86 Palmes tubes were exposed at various conditions: wind velocities ranging from 0.15 to 2.3 m s−1, temperatures from 2°C to 40°C and relative humidities from 20% to 85%. The main information is the high increase of sampling rate with increasing wind velocity. The formation of eddies at the open end of tube induces a reduction in the effective length of diffusion. This reduction starts up from the weak velocities of wind (i.e. 0.3 m/s) and is estimated at 47% for 2 m s−1. Influences of temperature and relative humidity give the weak deviations, exceeding 10% only under unusual conditions (T>30°C and RH>80%). Under common conditions, the sampling rate regularly increases to 0.3%/°C with temperature. Some practical solutions are proposed in this study to improve the accuracy of measurements. The use of a protective device and application of a corrective function appears through these results as effective means to correct the effects of meteorological factors on the sampling rate of tube.