Development and application of a sensitive method to determine concentrations of acrolein and other carbonyls in ambient air.

Acrolein, an unsaturated aldehyde, has been identified as one of the most important toxic air pollutants in recent assessments of ambient air quality. Current methods for determining acrolein concentrations, however, suffer from poor sensitivity, selectivity, and reproducibility. The collection and analysis of unsaturated carbonyls, and acrolein in particular, is complicated by unstable derivatives, coelution of similar compounds, and ozone interference. The primary objective of this research was to develop an analytical method to measure acrolein and other volatile carbonyls present in low part-per-trillion concentrations in ambient air samples obtained over short sampling periods. The method we devised uses a mist chamber in which carbonyls from air samples form water-soluble adducts with bisulfite in the chamber solution, effectively trapping the carbonyls in the solution. The mist chamber methodology proved effective, with collection efficiency for acrolein of at least 70% for each mist chamber at a flow rate of approximately 17 L/min. After the sample collection, the carbonyls are liberated from the bisulfite adducts through the addition of hydrogen peroxide, which converts the bisulfite to sulfate, reversing the bisulfite addition reaction. The free carbonyls are then derivatized by o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA*), which stabilizes the analytes and makes them easier to detect by electron-capture negative ionization mass spectrometry (ECNI-MS). The derivatives are then extracted and analyzed by gas chromatography-mass spectrometry (GC-MS). The mist chamber method was applied in a field test to determine the extent of acrolein in ambient air near the Peace Bridge plaza in Buffalo, New York, an area of heavy traffic near a major border crossing between the United States and Canada. In addition, XAD-2 adsorbent cartridges coated with 2-(hydroxymethyl)piperidine (2-HMP) according to Occupational Safety and Health Administration (OSHA) Method 52 and passive samplers based on the use of dansylhydrazine (DNSH) were deployed at this location at the same time, which provided the opportunity to compare methods. The mist chamber results showed that the Peace Bridge traffic was clearly a source of acrolein, with an average concentration of 0.26 microg/m3 at a site 152.4 m downwind (northeast) of the plaza. The OSHA cartridges proved to be too insensitive to determine ambient acrolein concentrations. The DNSH passive samplers returned concentrations near the limit of detection; hence the values were a little higher and less consistent than those in the mist chamber results. The optimized mist chamber method was then applied to determine atmospheric acrolein concentrations at three sites in northern California: a site chosen to reflect the hemispheric background, a region dominated by biogenic sources, and an urban environment. The resulting average acrolein concentrations were 0.056, 0.089, and 0.290 microg/m3, respectively, and the limit of detection was 0.012 microg/m3 The consistency of the replicate samples obtained in the field was good, with the relative standard deviations (RSDs) ranging from 19% at the hemispheric background site to 3% at the urban site. The advantage of the current mist chamber method is that it can determine ambient acrolein concentrations over short time periods with enough sensitivity to be effective even in relatively "clean" environments. This allows for the determination of temporal patterns related to acrolein concentrations, such as diurnal cycles of reaction kinetics. The main disadvantages of the method are that it is laborious and time-consuming and requires specialized equipment that makes it difficult to utilize for routine monitoring of acrolein.