From the text...'Concurrent side by side operation of a standard high volume sampler and one fitted with an Andersen impactor has indicated that wind interference can result in lower total suspended particulates (TSP) being measured by the standard high volume sampler than by the impactor equipped sampler. This effect is particularly noticeable during very high TSP days which were characterized by dust storms and high wind conditions. In this case, the two measurements often disagree by more than a factor of 2. Slightly higher TSP levels are also measured by the impactor if an appreciable time lapse occurs between the sampler shut down and subsequent filter collection.'