Formaldehyde and acetaldehyde are listed by the United States Environmental Protection Agency (U.S. EPA) as urban air toxics. Health effects due to significant exposure to these air toxics include increased incidence of nasopharyngeal cancer, myeloid leukemia, and exacerbation of asthma. Determining the spatial variation of air toxics, such as acetaldehyde and formaldehyde, is important for improving health risk assessment and evaluating the effectiveness of source control and reduction programs. Here, a pilot study was designed and performed to investigate small-scale spatial variability in concentrations of aldehydes using passive samplers. A literature review was first completed to select and evaluate current passive sampling and analysis methods. Radiello Aldehyde Samplers and high performance liquid chromatography (HPLC) were selected for sampling and analysis, respectively. An HPLC instrument was then set-up for separation with an Allure AK (aldehyde-ketone) column and for detection of aldehyde-derivatives via ultraviolet-visible (UV-Vis) spectrometer at 365 nm. Samplers were deployed in an (approximately) 0.7 km resolution grid pattern for one week in January 2010. Collected samples and blanks were eluted with acetonitrile and analysis was performed with the HPLC. Aldehyde samples were quantified using calibration standards. Mean aldehyde concentrations were 3.1 and 1.2 =/ mg/m³ for formaldehyde and acetaldehyde, respectively, and mean acetaldehyde/formaldehyde concentration ratios were 0.4. The concentration ratios showed very little variation between sites, and correlation of aldehyde concentrations by site was high (r=0.7). Therefore, it is likely that both aldehydes have similar sources. Spatial variation of aldehyde concentrations was small within the sampling area, as displayed by low coefficients of variation (13 and 23% for formaldehyde and acetaldehyde, respectively) and small concentration differences between sites (average of both aldehydes less than 0.5 mg/m³). Thus, one sampler may be representative of this sampling area and possibly other areas of the same spatial scale. Methods established during this pilot study will be used in a larger field campaign to characterize the spatial distribution of concentrations throughout the county, for analysis of environmental equity and health impacts.