In contrast with normal onshore wind, Santa Ana winds bring dry, hot air towards the coast, originating from inland mountains and deserts. Fungal spores can be transported out of central California by Santa Ana winds. Movement of fungal spores is an important environmental concern because they contribute strongly to ecosystem function and also can infect humans and agricultural crops. Spores under 2.5 microns are of particular importance because at this size particulate matter can get lodged deep in the lungs and even enter the bloodstream. Spores can be picked up along with dust during arid conditions. We hypothesized that fungal spore counts will be higher during SAOs and will be positively correlated to temperature and negatively correlated to relative humidity.
From March 2015 to March 2016, we deployed a high-volume sampler, which collected particulate matter smaller than 2.5 microns. Atmospheric sampling intervals for individual filters ranged from approximately 2 to 25 days. The filters were washed in a saline solution to suspend the spores in liquid. Spore counts were performed using a Neubauer hemocytometer under a microscope. Climate factors, including temperature, relative humidity, wind speed, wind direction, and rainfall were taken from a weather station 2.5 mi away.
After analyzing samples from the first six months of our sampling effort (i.e., March 2015-September 2015), there was a significant difference in spore concentration between Santa Ana events and offshore wind conditions (F = 10.46, p = 0.005). Spore concentration did not significantly vary with average temperature during each sampling period (F = 0.955, p = 0.342) but was significantly related to relative humidity (F = 30.14, p < 0.001). Spore concentration was not significantly related to the climate conditions of the previous three days before each sampling period (event – F = 0.032, p = 0.861), relative humidity – F = 2.103, p = 0.165, temperature – F = 0.012, p = 0.914). The results partially support the hypothesis. Spore concentration increased during SAOs and decrease with relative humidity. However, there is no relationship between temperature and airborne spore concentration.