Atmospheric levels of formaldehyde and acetaldehyde and their relationship with the vehicular fleet composition in Salvador, Bahia, Brazil

The present work is concerned with the formaldehyde and acetaldehyde content in the gas-phase and their concentrations correlation, with the vehicular fleet, at several sites in Salvador, BA, Brazil. The samples were collected using C-18 Sep Pak cartridges coated with an acidic solution of 2,4-dinitrophenylhydrazine (DNPH). The resulting hydrazones were separated and quantified using HPLC. Samples were collected during 1 - 2 h periods at six sites located in the city of Salvador, Bahia: a bus station, a tunnel, a commercial mall parking lot, a business building parking lot a residential district and a commercial district; and at two other sites far from Salvador: Cacha Pregos and Lagoa Verde. The measured concentrations for formaldehyde and acetaldehyde ranged, respectively, from 0.20 to 88 ppbV and from 0.40 to 93 ppbV. The formaldehyde/acetaldehyde concentration ratio determined in these sites were: 0.66 (commercial mall parking lot); 0.65 (business building parking lot); 4.4 (bus station); 1.2 (tunnel); 1.0 (residential area), 1.7 (commercial area), 1.1 (Cacha Pregos) and 0.8 (Lagoa Verde). In the case of the tunnel, it represents the hole vehicular fleet of the city. Traffic counts taken during the sampling periods indicated that 82% of the vehicles at that site were light duty engines and 18% were heavy duty vehicles. A simple calculation using the tunnel fleet composition and the ratio formaldehyde/acetaldehyde at the bus station (as a diesel signature) and at the parking (as a light duty vehicles signature) revealed an expected tunnel ratio of 1.3 which is very close to the measured ratio 1.2. Indeed, the expected ratio for both the commercial area and residential area was, respectively, 1.7 and 0.62. It allows us to conclude that the atmospheric level of formaldehyde and acetaldehyde in Salvador has a close relationship with the vehicular fleet composition.