Formaldehyde and acetaldehyde in the atmosphere of Salvador-Ba, Brazil, using passive sampling

Among the aldehydes in the atmosphere, formaldehyde (HCHO) and acetaldehyde (CH3CHO) are the most abundant ones. They have great relevance to the atmospheric chemistry for configuring the main source of free radicals and precursors of organic aerosol in urban areas. These compounds are predominantly emitted by mobile sources and present a prejudicial impact to the human health and to the environment. A passive sampler (PS) was optimized to measure the concentrations of HCHO and CH3CHO in the atmosphere of Salvador city, Bahia, in Brazil, in amply distributed points and at a low cost. The optimized passive sampler was based on the molecular diffusion of the gas through a static layer of air and was composed by a cylindrical body made of polyethylene with a teflon membrane in the air inlet, protected by a stainless steel screen; following the diffusion space, there was a glass fiber filter impregnated with 2,4-dinitrophenylhydrazine solution 30 mmol L− 1 + glycerol 1 mol L− 1. The hydrazones fixed in the impregnated filter were extracted with 1.5 mL of acetonitrile and then determined by high-performance liquid chromatography with UV-vis detection at 360 nm. The sampling method was validated by comparison with active sampling, showing accuracy within the tolerated error by the European Union, of ± 25% (formaldehyde, 9.8% and acetaldehyde, 14%). The ozone average concentration of 36 μg m− 3 did not interfere in the passive sampling of formaldehyde and acetaldehyde. The precision of the measurements were 6.6 and 15% respectively, represented as relative standard deviation. During the rainy period, the concentrations found in the atmosphere of the city varied from 2.3-4.8 μg m− 3 for formaldehyde and < 1.2-1.9 μg m− 3 for acetaldehyde. In the dry period, the concentration ranges were presented as 1.5-18 μg m− 3 for formaldehyde and < 1.2-19 μg m− 3 for acetaldehyde. In this period, the atmospheric concentrations found increased significantly, influenced by the intensity of the vehicle fleet, combined with meteorological conditions. The ratio [HCHO]/[CH3CHO] showed predominance of aldehydes formation in situ in the rainy season, and direct emission, mainly vehicular, in the dry period.