Chemiluminescent method for continuous monitoring of nitrous acid in ambient air

Abstract

A continuous-flow method for measuring atmospheric HNO2 concentration in real time has been developed that uses a chemiluminescent NOx monitor. A Na2CO3 solution strips gaseous HNO2 from the atmosphere by means of pulling an air sample and the solution through a glass coil and mixing continuously with ascorbic acid solution which reduces nitrite to NO. The mixture is led into a gas-liquid separating coil consisting of microporous PTFE tubing. The NO evolved from the separating coil is swept out by a stream of clean air and detected with a chemiluminescent NOx monitor. The technique utilizes a dual flow system and dual channel NOx monitor to correct positive interferences from NO2 and peroxyacetyinitrate (PAN). The concentration of HNO2 is determined by difference between the two measurements. Sensitivity of the method is a function of the ratio of sampling flow rate to carrier gas flow rate, which permits readily a highly sensitive measurement.

A Microporous Membrane-Based Continuous Generation System for Trace-Level Standard Mixtures of Atmospheric Gases

“…The decreasing trend for the HNO2 output was similar to those of NO and SO2, but the output was not in inverse proportion to the purge gas-flow rate. An identical result was obtained in our previous continuous-generation system for HNO2 vapor, 6 which was based on a bubbling technique, where the purge gas passed through a mixture of NaNO2 and H2SO4 solutions. In this system, the purge gas-flow rate was found to significantly affect the purity of the output as well as the HNO2 output, and working at high flow rates of purge gas was found to be advantageous for an efficient generation of high-purity HNO2.…”

“…Because the converter efficiently reduces not only NO2 but also HNO2 to NO, it allows sequential measurements of NO and the sum (NO + NO2 + HNO2) by bypassing and passing through the converter, respectively. Our previous results 6 showed that HNO2 is quantitatively removed from the gas stream by a single Na2CO3-impregnated cellulose filter. This implies that the sum measured by passing through the Na2CO3-filter provides NOx (NO + NO2).…”

“…Of these reactions, the reduction of nitrite to NO with ascorbic acid was investigated in our previous work, 6 and the maximum reduction efficiency was obtained at an ascorbic acid concentration above 0.05 M and a H2SO4 concentration of between 0.02 and 0.1 M. The other two reactions were the decomposition reaction by H2SO4.…”

“…The generation coil was identical to the gas-liquid separating coil that was used for measurements of atmospheric HNO2 and HNO3. 6,7 The system is, so to say, a flow-type source, whereas the Dasgupta's system is a batch-type source. The proposed flow-type generator offers generation based not only on Henry's law, but also on chemical reactions, leading to a distinct advantage concerning the availability of continuous sources for various compounds.…”

UV‐visible absorption cross sections of nitrous acid

“…Another method, the wetted wall denuders, has been presented in the last years [Vecera and Dasgupta, 1991;Simon and Dasgupta, 1995]. A continuous method based on the conversion of nitrite to NO followed by a detection by chemoluminescence has also been used [Kanda and Taira, 1990]. These methods are user-friendly and relatively inexpensive, but special care has to be taken to avoid cross sensitivities with other atmospheric species; therefore they require much experimental work [Febo et al, 1993].…”