Outdoor air sampling for pollen and fungal spores is commonly done with the Burkard Volumetric Spore Trap. Because counting the entire slide surface is impractical for routine monitoring, two counting methods are generally used: the single longitudinal traverse method (SLM) and the twelve transverse traverse method (TTM). SLM is fast and provides a good approximation of the average daily spore concentration. TTM takes more time, however, it gives a better approximation of the average daily spore concentration and senses diurnal rhythm. TTM is usually considered too time consuming for routine use.
To find a spore counting method that shows changes in spore concentrations during the course of a day but takes less time than the TTM, the 28 fields method was devised. The 28 fields method is a variant of the TTM in which only 28 fields are counted per traverse. To test this method, the twelve traverses per slide were counted twice. For each traverse, the entire traverse was counted, then 28 fields were recounted. The bihourly spore concentrations were then calculated and compared statistically using the Wilcoxon Paired-Sample test and Spearman's Correlation. The data shows that the 28 fields method senses fluctuations in bihourly spore concentration which are parallel to those of the TTM. This indicates that 28 fields method may be considered as an alternative to the TTM for routine monitoring of spore concentrations.