MAGNETIC SUSCEPTIBILITY OF TREE LEAVES AS A SIMPLE, COST-EFFECTIVE MEANS OF MONITORING ATMOSPHERIC PARTICULATE MATTER CONCENTRATIONS ALONG THE WASATCH FRONT, UTAH

The high cost of air quality monitoring stations makes it difficult for citizens or local governments to monitor air quality in their own neighborhoods, especially in low-income communities. For example, three counties along the Wasatch Front in Utah that are heavily impacted by air pollution (Davis County, Salt Lake County, Utah County) have a combined area of 3585 mi², but only seven stations that monitor either PM-2.5 (particulate matter concentration smaller than 2.5 microns) or PM-10. The objective of this study is to find a much cheaper method of measuring air quality so that the air quality can be measured at more locations in and around cities. The objective was addressed by measuring the magnetic susceptibilities of the leaves of the 10 species of trees most common in urban areas of the Intermontane West (blue spruce, box elder, green ash, honey locust, linden, Norway maple, oak, pine, poplar, Siberian elm) within a two-mile radius of each of the seven monitoring stations in the three counties over a three-year period (2013-2015). After air-drying to constant weight and crushing the samples, both low-frequency (0.46 kHz) and high-frequency (4.6 kHz) magnetic susceptibilities were measured with the Bartington MS3 Magnetic Susceptibility Meter. The most promising linear relationships thus far have been the prediction of the three-month average PM-10 by the high-frequency magnetic susceptibility of Siberian elm (Ulmus pumila) leaves (R² = 0.9967, P = 0.03) and the low-frequency magnetic susceptibility of box elder (Acer negundo) leaves (R² = 0.995, P = 0.04), the prediction of the one-year average PM-10 by the low-frequency magnetic susceptibility of blue spruce (Picea pungeus) needles (R² = 0.961, P = 0.01), the prediction of the three-year average PM-10 by the high-frequency magnetic susceptibility of pine (Pinus nigra) needles (R² = 0.9408, P = 0.03), and the prediction of the one-year average PM-2.5 (R² = 0.3037, P = 0.04) and the one-year average PM-10 (R² = 0.5835, P = 0.02) by the low-frequency magnetic susceptibility of pine needles. As expected, magnetic susceptibilities of conifer needles tend to predict particulate matter concentrations averaged over one to three years, while magnetic susceptibilities of deciduous leaves tend to predict particulate matter concentrations over the previous three months.