RESUMO
A study of the equivalence to the reference methods of the Radiello samplers for ozone (O(3)) and benzene as well as the membrane-closed Palmes tube (MCPT) for nitrogen dioxide (NO(2)) is presented. These samplers benefit from new model equations capable of estimating their uptake rate. For O(3), the aim here was to demonstrate the equivalence for the reference period of 8 h and 120 microg m(-3), the target value of the 3rd European Daughter Directive. For benzene, the demonstration of equivalence to the annual limit value of 5 microg m(-3) of the 2nd European Daughter Directive was examined. In the case of NO(2), the equivalence to the annual limit value of the 1st European Daughter Directive (40 microg m(-3)) was considered. Results show that the radial sampler for O(3) fails to meet the Data Quality Objective (DQO) for continuous monitoring. However, with an expanded uncertainty of less than 30%, the O(3) diffusive sampler fulfils the DQO for indicative measurements. For benzene, the Radiello sampler exposed for 7 days gave satisfying results showing the ability of the sampler to meet the DQO of the reference method. Nevertheless, the field tests should be complemented by measurements for a wider range of benzene concentrations. In the case of NO(2), all the results of the laboratory and field experiments respected the requirements necessary for the demonstration of equivalence. Overall, these findings thus show that the Radiello sampler and the MCPT are equivalent to the reference methods only for assessment of benzene and NO(2), respectively.
Assuntos
Poluentes Atmosféricos/análise , Benzeno/análise , Dióxido de Nitrogênio/análise , Ozônio/análise , DifusãoRESUMO
This study presents an evaluation of the extent of differences between measurements performed by O(3) and NO(2) diffusive samplers and by the reference methods for diffusive samplers commercially available. The tests were performed in an exposure chamber under extreme conditions of controlling factors and under field conditions. For NO(2), the results of the laboratory experiments showed that most of the diffusive samplers were affected by extreme exposure conditions. The agreement between the samplers and the reference method was better for the field tests than for the laboratory ones. The estimate of the uptake rate for the exposure conditions using a model equation improved the agreement between the diffusive samplers and the reference methods. The agreement between O(3) measured by the diffusive samplers and by the reference method was satisfactory for 1-week exposure. For 8-hour exposures, the diffusive samplers with high uptake rates quantified better the O(3) concentration than the samplers with low uptake rates. As for NO(2), the results of the O(3) field tests were in better agreement with the reference method than the ones of the laboratory tests. The field tests showed that the majority of diffusive samplers fulfils the 25% uncertainty requirement of the NO(2) European Directive and the 30% uncertainty requirement of the O(3) European Directive for 1-week exposure.
Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental/instrumentação , Dióxido de Nitrogênio/análise , Ozônio/análise , Difusão , Monitoramento Ambiental/métodos , LaboratóriosRESUMO
This paper presents the results of a feasability study for the preparation and certification of reference materials (RMs) for nitrogen dioxide (NO(2)) and sulfur dioxide (SO(2)) in diffusive samplers. RMs for NO(2) were prepared by exposure to gas mixtures in a chamber while the RMs for SO(2) were prepared by liquid spiking. Certification of RMs for NO(2) was found feasible with a certified uncertainty of 5.8% and a proposed shelf life of 5 years. The uncertainty was calculated with contribution from the homogeneity of preparation, stability and transport of the CRMs and from an external verification of the certified value. To reach 5.8% of uncertainty, the contribution of the differences between the results of analysis by ion chromatography and colorimetry must be eliminated. It is proposed to solve this by pre-extracting the samplers with water before analysis. The results of this study indicate that the samplers are stable for at least two years before and after exposure when stored in a refrigerator. By contrast, the certification of RMs for SO(2) was found to not be feasible due to instability problems. This instability was attributed to reaction of sulfate on the walls of the samplers. Alternatively, the preparation of RMs by simultaneous exposure to SO(2) and NO(2) has been tested. Satisfying homogeneities has been reached both for NO(2) and SO(2).
Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental/normas , Dióxido de Nitrogênio/análise , Dióxido de Enxofre/análise , Certificação , Difusão , Estudos de Viabilidade , Padrões de ReferênciaRESUMO
The influence of environmental parameters on the uptake rate of the nitrogen dioxide (NO(2)) Palmes diffusive sampler was investigated. The main factors affecting the uptake rate were found to be wind speed, the preponderant factor, followed by relative humidity and temperature. The NO(2) concentration and exposure time, as well as the interactions among the factors were not found to have a significant influence on the uptake rate of the Palmes sampler. As a result, a model able to predict the uptake rate of the Palmes sampler was established. In addition, by using the model-predicted uptake rate, the agreement between chemiluminescence and the Palmes sampler during the field tests was improved. The NO(2) Palmes diffusive sampler was shown to comply with the requirement on accuracy defined by the European Directive for the indicative methods of measurements.