Magnetic Susceptibility of Tree Leaves as a Simple, Cost-Effective Means of Monitoring Air Quality

Ryan D. Heaslet, Lucas Lloyd

Abstract


Thehigh cost of air quality monitoring stations ($10K - $70K, not includingmaintenance and operation) makes it difficult for citizens or local governmentsto monitor air quality in their own neighborhoods, especially in low-incomecommunities. For example, Utah County, Utah, with an area of 2141 mi2,has only four air-quality monitoring stations: (1) north Provo close to bothProvo High School and Brigham Young University (2) Spanish Fork Airport (3)near State Street in Lindon (4) just south of SR-92 on 6000 W in Highland. Theair-quality stations monitor levels of CO, NO2, O3,PM-2.5 (particulate matter smaller than 2.5 microns), and PM-10. The objectiveof this study was to find a much cheaper method of measuring air quality sothat the air quality can be measured at more locations in and around cities.The objective was addressed by measuring the magnetic susceptibilities of fortyleave samples including 12 species of trees (cypress, crab apple, elm,flowering pear, green ash, honey locust, linden, Norway maple, pine, red maple,Russian olive, spruce). Ten samples were collected within a two-mile radius ofeach of the four air-quality monitoring stations in Utah County. Afterair-drying and crushing the samples, both low-frequency (0.46 kHz) andhigh-frequency (4.6 kHz) magnetic susceptibilities were measured with theBartington MS3 Magnetic Susceptibility Meter. The best correlations betweentree leaf magnetic susceptibilities and air-quality parameters were between thethree-year average of PM-2.5 and the high-frequency magnetic susceptibility ofleaves of pine (Pinus aristata) (R2= 0.87) and Norway maple (Acer platanoides)(R2 = 0.86). The correlation was used with measured high-frequencymagnetic susceptibilities of pine to estimate PM-2.5 in two unmonitoredlocations heavily impacted by highway traffic (corner of 800 N and I-15 andcorner of University Parkway and I-15, both in Orem, Utah) on one day in August2013. It was found that estimated levels of PM-2.5 were 9.5µg/cm3 and8.9µg/cm3, respectively, which were below the EPA PM-2.5 annual standard forUtah which is 12 µg/cm3. Further results included samples tested inSalt Lake County, Utah County, as well as in Kentucky while at NCUR.

Keywords


Leaf, Magnetic Susceptibility, PM-2.5

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