During the TRAnsport and Chemical Evolution over the Pacific-2001 (TRACE-P-2001) aircraft mission, formaldehyde (CH2O) and acetaldehyde (CH3CHO) were measured along with an extensive suite of other atmospheric parameters. CH3CHO was measured with two different instruments, one developed by NCAR and another developed by NASA. There were disagreements, at times, between the CH3CHO measurements. There was also disagreement between the CH3CHO datasets and a simple photochemical box model, although CH2O measurements agreed with the model. It is important to model and measure both gases correctly because they are intermediate oxidation products of volatile organic compounds (VOCs), and they decompose into hydroperoxyl radicals (HO2) and carbon monoxide (CO). The objective of this study was to explore the relationship between CH2O and CH3CHO in the troposphere. The relationship of CH2O vs. CH3CHO was examined for five different altitude ranges up to 12 km. Each altitude range was parsed into clean and polluted air masses; “polluted” was defined as nitric oxide (NO) greater than 50 parts per trillion by volume or CO greater than 169 parts per billion by volume. Slope and linear regression correlation coefficients were compared. The following patterns were observed for the individual CH3CHO datasets in relation to CH2O. CH3CHO decreased with altitude, but more slowly than CH2O. Correlation between CH3CHO and CH2O was driven by polluted air, although this correlation decreased with altitude.