Formaldehyde levels in downtown Mexico City during 2003

In this study, two spectroscopic techniques and two DNPH-sampling techniques were operated simultaneously in a downtown site of Mexico City to accurately determine formaldehyde levels during February and October of 2003. 1-hour samples from DNPH-silica cartridges and 4-h samples with an annular denuder system were collected during 4 days. The results are compared with the continuous data provided by an open-path Fourier transform infrared spectrometer (OP-FTIR) and a differential optical absorption spectrometer (DOAS) along a 426 m trajectory. Both spectroscopic techniques showed an agreement of 15% or less and a correlation coefficient of 0.86. The cartridge results presented average deviations relative to the OP-FTIR between −32% and 24% for the specific time periods but showed a clear similarity in the temporal patterns from the 5-min spectroscopic data. The results from the annular denuder samples show more limited precision (−35-65%) but the overall accuracy, when all data collected for the two 4-h periods was averaged, fell within a ±15% deviation range. This sampling configuration allowed to estimate an amount of formaldehyde in the particulate matter (<2.5 μm) of about 20% from that found in the gas-phase. Monthly average concentrations ranged between 23.9 ppb during February and 12.7 ppb during October of 2003. A 35% decrease in the average-peak values between the dry and wet seasons was identified.