Impactor samples

Most of the published composition/size distribution data have been obtained by analyzing cascade impactor samples. Some of these data suffer from poor size classification as a result of particle bounce or reentrainment, seriously limiting size resolution. Even when this problem is overcome, the data obtained with conventional cascade impactors are not capable of resolving many details of the distribution of submicron particles. These instruments typically classify only those particles larger than 0.3-0.5 tam aerodynamic diameter. All smaller particles are collected on a filter downstream of the impactor. Some measurements of the variation of composition with size below this limit have been attempted by aerodynamically classifying resuspended ash ( ). These data suffer from incomplete disapregation as well as poor classification of the smaller particles. 

Only a small fraction of these particles is included in the impactor sample because the cyclone separator removed most particles larger than about 2 urn. The composition of those large particles which were collected by the impactor is that expected for the ash residue. The major species are the oxides of Si,... 

Sampling. Four aerosol samples were collected isokinetically on July 26, 1979, at ports on the inlet duct of the ESP at Plant A two were taken with 62-mm fluoropore filters and two were taken with the University of Washington MKV Cascade impactor (1 ). At plant D, samples were collected over a 6-day period at ports both in the outlet duct of the ESP (i.e., upstream of the FGD system) and at the 91-m level of the stack. Eleven fluoropore filter, 1 MKV, and 4 MKIII impactor samples at each location, giving a total of 22 filter, and 8 MKIII samples. A single MKV sample was also collected in-stack at reduced pressure at plant D during the 6-day period. Polycarbonate material coated with apiezon L vacuum grease and 62 or 47-mm-diam, l-pm pore Fluoropore filters were used as back-up filters in the MKV impactor. 

Table I. Log-normal distribution parameters and selected analyses of particles on stages of impactor sample MKV-l. ...

Approximate times of polluted (P), continental (C), and marine (M) air masses are indicated based on synoptic weather maps and consistent with aerosol composition measurements. Times of impactor samples, taken in duplicate concurrently with the streaker, are indicated at the top as midpoints of alternating 10- and 12-h sampling periods. 

Figure 3. Particle size distributions of crustal elements Al, Si, Ca, and Ti averaged during March 16-19 (for impactor sample numbers indicated, cf. Figure 1) when concentrations were high enough to provide accurate data in the fine fractions.

Cleans and standard deviations of 5 sampling periods (7 impactor samples) W ... 

Van Vaeck, L K. Van Cauwenberghe, and J. Janssens, The Gas-Particle Distribution of Organic Aerosol Constituents Measurement of the Volatilization Artifact in Hi-Vol Cascade Impactor Sampling, Atmos. Environ., 18, 417-430 (1984). 

Improvement in sensitivity and range of nondestructive analyses from impactor samples is needed, especially in the methods for detecting total particulate mass and organic species. 

One other in situ technique can be used to determine fractional acidity in atmospheric aerosols by means of Fourier transform infrared (FTIR) spectroscopy (46). Originally, impactor samples were collected and were pressed into a KBr matrix, and then the IR spectrum was taken by attenuated total reflectance (ATR) FTIR spectroscopy to determine relative acidity, based on differences in absorption bands for sulfate and bisulfate species. Aerosols with [H+]/[S042 ] ratios greater than 1 could also be qualitatively identified. More recent innovations in the FTIR technique (47, 48) have made possible... 

Diffusive deposition of gases. Although we have not formally investigated the deposition of condensible gases, the overall concentrations of Br and Se in impactor samples collected downstream of a hot-side ESP at a large western coal-fired power plant far exceeded their concentrations as determined by filter sampling (16). In addition, the concentrations of Br and Se were nearly uniform on all stages... 

Marple, V. A., and Rubow, K. L., Cascade Impactor, Sampling and Data Analysis, American Industrial Hygiene Association, Akron, Ohio, 1986, p. 79. 

Lodge, J.P. Chan, T.L. (1986). Cascade impactors Sampling data Analysis. American Industrial Hygiene Association Akron, OH. 

Simplified layout of an impactor sampling train. (From Pilat et al. [13], with... 

Sample pretreatment is dependent on the sampling method. VOCs collected on adsorbents are typically desorbed thermally directly into the GC. The filter and impactor samples typically require extraction into a suitable solvent, such as n-hexane or a mixture of n-hexane acetone, although thermal desorption can be utilised also for filter samples. 

Solvent extracts of impactor samples (particulate firaction) and PUF plugs (gaseous fraction) were analysed for genotoxicity, AhR-mediated activity, anti/estrogenic and anti/androgenic activities using in vitro bioassays. 

A type of personal air sampling instrument that incorporates a glass tube containing a liquid medium. This reacts either chemically or physically to dissolve the contaminant. A known volume of air is passed through the impinger and the liquid is analyzed by gas chromatography or photospectrometry. See also Impactor (Sampling). Implosion... 

A 400-jet impactor samples a bioaerosol at 28 L/min for 20 minutes. If 344 colonies are counted, what is the average airborne number concentration of viable particles. Assume no loss of viability during sampling. 

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