C1-C5 carbonyl compound concentrations were measured at four sites; three urban sites in the Mexico City
Metropolitan Area (MCMA) and a rural site in the state of Morelos during the period 2006–2007. Formaldehyde,
acetaldehyde and acetone were found to be the most abundant carbonyls, with acetone showing the highest levels at all
sites. Concentrations were highest in winter at all sites and lower in summer and autumn. These decreases in
concentration are explained by the influences of both photochemical reactions and local meteorological conditions. The
strong correlation between C1-C2 and C3 indicated a common origin for these carbonyls. This was supported by a factor
analysis which showed high loading on C1-C2 and C3. The C1/C2 ratios varied between 0.77 to 1.19, values which can be
considered typical of an urban area.