Research Journal of Chemical Sciences ______ ______________________________ ______ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 89 - 92 , May (201 2 ) Res.J.Chem.Sci. International Science Congress Association 89 Short Communication Influence of Temperature and Relative Humidity on the Performance of Nitrogen Dioxide Diffusive Sampler Šerevičienė V. and Paliulis D. Department of Environment Protection, Vilnius Gediminas Technical University, Vilnius, LITHUANIA Available online at: www.isca.in (Received 8 th March 201 2 , revised 1 4 th March 201 2 , accepted 14 th March 201 2 ) Abstract Passive diffusive samplers provide an excellent opportunity to perform indicative measurements or establish a dense network o f measuring sites. This paper describe and present the results of experiments in exposure chamber to determine the effects of different ambient air temperature (T) and relatively humidity (RH) on the performances of passive diffusive samplers for measuring nitrogen dioxide (NO 2 ) in the outdoor environment. In experimental studies were used passive diffusive samplers with stai nless steel grids and impregnating solution of 10% (v/v) triethanolamine (TEA) with water. During these researches in laboratory chamber passive samplers was exposed at various conditions: temperature from 10C to 40C and relatively humidity from 30% to 8 0%. During these variations in conditions NO 2 concentration was constant, approximately 40 μg/m 3 . Influence of temperature and relative humidity are weak on passive sampler performance when ambient temperature is 20C and relatively humidity 60%. Changing environmental conditions (T � 30 C and RH � 75 %) indicates accuracy of passive samplers 10 – 35% when compared to co - located continuous NOx analyzer. Keywords: nitrogen dioxide, diffusive sampling, air monitoring, temperature, relatively humidity, laboratory chamber. Introduction Nitrogen dioxide (NO 2 ) is common combustion related pollutant that is mostly formed from oxidation of nitric oxide (NO) which is produced during high temperature burning of fuel in cars and other road vehicles, heaters and cookers 1 – 3 . Nitrogen dioxide is considered to be an important atmospheric trace gas pollutant because of its effects on health 4,5 . Generally NOx monitoring is carried out using high volume samp lers, handy samplers or through a chemiluminescence analyser. Such instruments require on site power source, apart from being capital intensive, involving complex operations and requiring specialist maintenance. In view of these limitations, extensive air quality monitoring over wide geographical areas presents serious difficulty. Passive samplers provide a convenient alternative for measuring ambient NO 2 in a highly cost effective manner 6 – 8 . Currently, passive samplers are being used to determine the air q uality in the work place, the living environment; and the ambient, outdoor environment including regional - scale air quality 9 – 11 . The passive sampler is based on the principle of diffusion of air. The atmospheric NO 2 diffuses up the tube where it gets abso rbed on the triethanolamine (TEA) coated mesh. This establishes a NO 2 concentration gradient along the length of tube, consequently NO 2 diffuses up the tube where it is absorbed on TEA coated meshes. Even though passive sampling has been widely used and r ecognized as a valuable tool in environmental monitoring, the reliability of this technique under varying environmental conditions is always a subject of controversy. Theoretical treatment using Fick’s laws of diffusion is based on the assump tion that ste ady - state conditions apply to passive samplers. In practice, this is not true, since the actual uptake of the analytes varies depending on factors like temperature and concentration, which define the two constants: diffusion coefficient in the case of diff usive samplers and permeability in the case of permeation samplers 12 - 16 . Environmental factors, such as temperature, relatively humidity, and wind speed can affect the performance of passive samplers 12,13 . Consideration of these environmental factors when selecting a sampler for field studies is important. Sampling rates determined under ideal conditions may not be valid across the varying environmental conditions that occur throughout a tipical sampling range of concentrations, wind velocity, temperature, and relative humidity 6,12,14 . Palmes claimed insignificant influence of temperature on the performance of passive samplers 17 . Other researchers conducted investigation results on the effect of temperature on the performance of passive samplers have shown that each 10◦C rise in temperature enhances 11 – 18 percent uptake by passive samplers 18 . Recent studies using stainless steel mesh and TEA solution, as an absorbing material, have shown insignificant effect of temperature on sample collection. An increased u ptake reported by early studies was probably because of the use of absorbing materials other than that of stainless steel mesh Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 89 - 92 , May (201 2 ) Res.J.Chem.Sci International Science Congress Association 90 (mainly Whatman filter paper) 19 . Over scientist also observed 25 percent increase in the NO 2 absorbance, when the relative humidit y rose from 0 to 100 percent 18 . Humidity is probably the most important environmental variable that affects the performance of passive diffusion samplers using TEA as absorbent, because TEA does not perform quantitatively at low humidities 20 . Although in t he use of passive samplers in the field, the effect of humidity is of not much consequence because the relative humidity of the ambient air is usually more than 40 percent. The aim of these performed researches is to investigate effects of temperature and relatively humidity to performance of diffusive samplers in laboratory chamber. Material and Methods The diffusive tube samplers applied in this study consists of the polypropylene tube approximately 34 mm long and 21 mm inner diameter and closely fitting cap. In one end of the diffusive tube is placed one stainless steel mesh ( f igure 1). For the preparation of diffusive tubes stainless steel mashes were impregnated with 10 % (v/v) solution of TEA and water. After exposure samplers were analysed in the laboratory spectrophotometrically using Saltzman reagent. Ten minutes are required for full coloured development before optical absorbance of the coloured solution is measured spectrophotometrically at 542 nm. The amount of nitrite ion in the sample is obtained with the help of calibration plot derived from standard nitrite solutions. The amount of extracted nitrite for samplers is used to calculate ambient NO 2 concentrations . The laboratory experiments were performed in an exposure chamber that all owed controlling of concentrations level, temperature and relative humidity. The exposure chamber size was 1.5 m lengthy, by 1.5 m width and by 1.8 m height with a volume of 4.05 m 3 . The nitrogen oxides in the chamber were obtained by means of the reaction between sulphuric acid and sodium nitrite. During the chemical reaction between sulphuric acid and sodium nitrite there are released nitrogen oxides into the air. 0.1 N sulphuric acid was dripped from burette into the glass with 20% aqueous soluti on of sodium nitrite to obtain expected NO 2 concentration. During the experiments in the exposure chamber, NO 2 was monitored using a chemiluminescence nitrogen oxides analyzer AC32M which was calibrated using a primary reference gas mixture. Its detectable limit is 0.4 μg/m 3 . To accelerate mixing of air in the chamber, the fan was used. The parameters of microclimate were measured in the chamber during experiment with data logger DrDAQ: temperature and relative humidity. Data were recorded automatically i n the computer. The sensors for temperature and relative humidity were placed at the 1 m height, in the same place were diffusive samplers are placed ( f igure 2). Figure - 1 Scheme of passive diffusive sampler The exposure conditions are chosen to cover a temperature range from 10C to 40C and relatively humidity from 30% to 80%. During these variations in conditions NO 2 concentration was constant, approximately 40 g/m 3 . Samplers were exposed for 1 week. Results and Discussion Passive diffusive samplers provide an excellent opportunity to perform indicative measurements or establish a dense network of measuring sites. This paper describe and present the results of experiments in exposure chamber to determine the effects of different ambient air temperatu re (T) and relatively humidity (RH) on the performances of passive diffusive samplers for measuring nitrogen dioxide (NO 2 ) in the outdoor environment. During these researches in laboratory chamber passive samplers was exposed at various combined conditio ns of temperature and relatively humidity to estimate the single effect of each factor and their interaction on the performance of passive diffusive samplers. Precision is a measure of the variability of response expected at any given concentration or various conditions. The relative standard deviation (RSD, %) is a common indicator of precision. Precision of diffusive samplers with 10% TEA/water impregnating so lutions is 5 – 7%. The accuracy of the passive samplers in comparison to chemiluminescence technique expressed as percent relative error (RE, %). During chamber experiments individual NO 2 diffusive tubes were generally in very good agreement with chemilumin escence measurements. Influence of temperature and relative humidity are weak on passive sampler performance when ambient temperature is 20C and relatively humidity 30%, accuracy 5% ( f igure 3). Worse accuracy (10%) was obtained during experiment when RH w as 35%. Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 89 - 92 , May (201 2 ) Res.J.Chem.Sci International Science Congress Association 91 Figure - 3 Accuracy of diffusive samplers obtained during experiments at various combined conditions of temperature and relatively humidity Changing environmental conditions (T � 35 C and RH � 80%) indicates accuracy of passive samplers 25% when compared to co - located continuous NOx analyser. Both the chemical reaction rate and the diffusion rate in the liquid phase are strongly temperature d ependent. Sampling rate of passive diffusive sampler is dependent to ambient temperature, because coefficient of molecular diffusion is temperature dependent. Two explanations are possible for the temperature dependence: either because the temperature modi fies the concentration of water vapo u r that influences the efficiency of NO 2 absorption by TEA, or because Fick’s coefficient of diffusion of NO 2 in air by 12 % between 20 and 40 C , and hence the sampling rate as well. High humidity can also alter the sorption behaviour of the exposed inner wall of tube - type samples or draught screen, particularly if condensation occurs 15 . 0 10 20 30 40 30 35 60 80 Accuracy, % Relative humidity, % 3 6 1 7 8 5 2 4 3 Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 5 ), 89 - 92 , May (201 2 ) Res.J.Chem.Sci International Science Congress Association 92 Conclusion Although passive diffusive samplers are extremely useful for estimating the spatial p ollutant concentrations, it is necessary to know the limitations for their adequate use in urban air monitoring. 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