Abstract

Lower carbonyls and n-alkanals from C₅ to C₁₀ were measured from late autumn 2000 to summer 2001 in two urban areas in the Algerian territory: Algiers and Ouargla. They were collected on silica cartridges coated with dinitrophenylhydrazine (DNPH) and pentafluorophenylhydrazine (PFPH), which were analysed by HPLC-UV and high-resolution GC-MS, respectively. The two methods were used in parallel samplings in a suburban Algiers site and provided consistent results for semi-volatile congeners, as differences in the concentration data did not exceed 21% on average for individual carbonyl levels ranging from 0.0 to 0.5–2.6 µg m⁻³. Concentrations of formaldehyde up to 27 and 5 µg m⁻³ were monitored during 10 h samplings in the daytime in Algiers and Ouargla, respectively; acetaldehyde reached values of 13 and 5 µg m⁻³, whilst acetone was the most abundant ketone with peak levels of 14 and 4 µg m⁻³, respectively. High night-time levels of lower carbonyls were also measured at both locations. Among the semi-volatile alkanals, the highest levels were observed in suburban Algiers for hexanal and nonanal (2.2 µg m⁻³) and in downtown Algiers for valeraldehyde (2.6 µg m⁻³), whilst in Ouargla only hexanal and nonanal levels within the C₅–C₁₀ fraction exceeded 1 µg m⁻³. Moreover, benzaldehyde concentrations as high as 5 µg m⁻³ were measured in the centre of Algiers. Algiers data are comparable with those found in photochemically polluted urban areas of Europe and the USA. Strong correlations between formaldehyde and acetaldehyde and between formaldehyde and benzaldehyde were observed; by contrast, acetone did not show any correlation with the lower aldehydes, suggesting the existence of carbonyl sources other than vehicular traffic. Diurnal variations of almost all carbonyls suggested that motor vehicles were the most important source in the winter, whereas photochemical production appeared to predominate during the summer.