Variation in Airborne Pollen Concentrations among Five Monitoring Locations in a Desert Urban Environment

The urbanization of the Las Vegas Valley has transformed this part of the Mohave Desert into a green oasis by introducing many non-native plant species, some of which are allergenic. Typically, one monitoring station is established per city to obtain pollen counts for an entire metropolitan area. However, variations in pollen concentrations could occur among different microenvironments. The objective of this study is to measure and compare pollen concentrations in five locations in Las Vegas to determine if there are significant differences between microenvironments within the city. Air samples were collected from five sites across the Las Vegas Valley over a 1-year period. Prepared slides were analyzed with a light microscope for pollen grains and converted into airborne pollen concentrations. Mixed model methods were used to determine mean differences. Tree pollen was the greatest contributor to the annual average airborne pollen concentrations (130 grains/m3) compared to weeds (6 grains/m3) and grass (3 grains/m3). The highest peak occurred in March 2016 (9589 total grains/m3). There were several differences among sites with respect to concentrations of individual tree species and for total weed and grass concentrations. We observed significant variations in concentration and composition among the five pollen collection stations that were established across the Las Vegas Valley. This study presented new outdoor pollen data for the southwest region of the USA, focused in Las Vegas. The results indicate that more sites and comprehensive monitoring of outdoor allergens are needed to provide accurate information to the community about outdoor air quality conditions

Evaluation of epifluorescence methods for quantifying bioaerosols in fine and coarse particulate air pollution

Despite being recognized as an important part of particulate matter (PM) air pollution and health risk, bioaerosols have not been quantified as extensively as other PM components for establishing PM standards and management strategies. The challenge lies partly in the lack of practical measurement methods. This study evaluated a filter-based, direct-staining fluorescence microscopy (DS-FM) method that may be adapted to routine air quality monitoring for bioaerosol concentration and size distribution. Through testing with bioaerosol standards made of bacterial cells and fungal spores, the method is shown to have precision, accuracy, detection limit, and dynamic range suitable for most ambient environments. DS-FM was demonstrated with PM samples from an arid urban location in Las Vegas, Nevada during the spring allergy season. Detectable bioaerosols ranged from 0.37 to 16 mu m in geometric diameter and averaged 0.27 +/- 0.23 cm(-3) in number concentration with about 2/3 and 1/3 in the fine ( 2.5 mu m) mode, respectively. The bioaerosol mass, estimated from the size distribution and an assumed density, was mainly in the coarse mode and accounted for 17 +/- 11% of PM10, 20 +/- 13% of PM10-2.5, and 4 +/- 3% of PM2.5 mass. Rain and high wind speeds appeared to elevate bioaerosol levels. Other advantages of DS-FM include low sample consumption and short turnaround times; a large amount of data can be generated by incorporating the measurement into current long-term air quality networks. Suggestions for using the data to inform bioaerosol origins, contributions, and public health impacts are discussed