Particulate Matter Contributions from Agricultural Tilling Operations in an Irrigated Desert Region

Sources of regional particulate matter (PM), particularly agricultural operations, must be understood in order to manage the air quality in irrigated dry climates. Direct monitoring measurements alone are useful, but not sufficient, to estimate regional PM source concentrations. This paper combines modeling with ground (point) and airplane (spatial) measurement methods to estimate regional PM10 (PM diameter≤10 μm) contributions from agricultural operations. Hourly data from three air quality monitoring stations positioned at a 2-m height located on the west and east mesas of New Mexico’s Mesilla Valley and in the valley at Anthony, NM were acquired from the New Mexico Air Quality Bureau. The study spanned the agricultural tilling season, March 1 to April 30, for the years 2008 to 2012. One- second spatial PM10 concentrations at 200 m above the valley floor were measured during a two-hour controlled field tilling operation on April 1, 2008. The HYSPLIT 4.0 (Hybrid Single-Particle Lagrangian Integrated Trajectory version 4) model was run at the corresponding times and heights, outputting PM10 concentrations from all potential agricultural tilling operations. The calculated percentage contribution (modeled PM10 concentration/measured PM10 concentration) indicated that the near-surface (2-m height) proportion from the agricultural operations for five seasonal averages ranged from 0.7% to 1.5% on the west and east mesas and 1.3% for the valley site at Anthony. There were 71 hourly high values of contribution ratios ranging from 30 to 100% at the three sites, depending on the wind speed and direction.