Desenvolvimento e validação de amostradores passivos para o monitoramento e poluentes atmosféricos

Abstract

Passive samplers are devices capable of taking samples of gas or vapor pollutants from the atmosphere without involving air active movement through them. The sampling rate is controlled by a physical process such as diffusion or permeation. The objective of this work was to develop and to validate passive samplers for the monitoring of NO2, O3, SO2 and H2S in outdoor environments aiming to cooperate with the growing of the spatial resolution and efficiency of atmospheric monitoring networks. The model of the used passive sampler was based on gas molecular diffusion through static air layer and consists of a cylindrical polyethylene tube (internal diameter 21 mm, length 12 mm) sealed at the bottom. To minimize turbulent diffusion and particle interference a stainless steel screen and Teflon membrane were used in the air inlet. After diffusion layer there was a cellulose filter which was impregnated with a specific reagent to trap the diffused gas. After exposure of the samplers the trapped gas in the form of the product reaction was extracted in an ultrasonic bath for 15 min. The absorbed SO2 as sulfite in the filter containing with 1.0 x 10-2 mol L-1 Na2CO3 was extracted with 1.5 mL of 1.0 x 10-2 mol L -1 H2O2 solution to ensure complete oxidation to sulfate, which was later determined by ion chromatography. The O3 reacted with nitrite ion of the impregnating solution (1.5 x 10-1 mol L -1 NaNO2 / 2.0 x 10-1 mol L-1 Na2CO3 / 1.0 mol L-1 glycerol) to produce nitrate ion, which was extracted with 1.5 mL of deionized water and also determined by ion chromatography. The absorbed NO2 in the impregnated filter with 5.0 x 10-1 mol L-1 KI / 2.0 x 10-1 mol L-1 KOH in methanol was extracted with deionized water and determined as NO2 - by UV-Vis molecular spectrophotometry. The trapped H2S in the impregnated filter with 5.5 x10-2 mol L-1 zinc acetate / 1.0 x 10-1 mol L-1 NaOH / 1.0 x 10-2 mol L-1 trisodic citrate was determined as sulfide by UV-Vis molecular spectrophotometry. The performance of the passive samplers was evaluated during exposure periods of 1 to 4 weeks in industrial influence areas next to the Industrial Complex of Camaçari-BA and urban area (Salvador-BA) as well as site presently used as pasture (former forest) in the Amazon region and petroleum fields (Buracica-BA). The precision of the measurements as relative standard deviation according to the obtained results from the simultaneously applied passive samplers varied between 2.4 and 12% for SO2, 2.0 and 15% for NO2, 2.5 and 16% for O3, 5.2 and 15% for H2S, in the following concentration levels ranging: 0.58 - 20 µg m-3 SO2, 1.1 - 21 g m-3 NO2, 14 - 51 g m-3 O3 and 0.40 - 3.0 µg m-3 H2S. The average accuracy (10 - 19%) was determined by comparison with simultaneous parallel measurements that were carried out with calibrated continuous monitors in industrial and pasture areas, and with diffusion tubes (denuder) in urban and pasture areas.