Airborne particulate size and concentrations in five Thoroughbred training yards in Newmarket (UK)

•The study evaluated airborne particulate size and concentrations in Newmarket training yards using a nephelometer.•Airborne particulates smaller than 2.5 μm (particulate matter [PM] 2.5) and 10 μm (PM10) were measured.•Maximum PM2.5 and PM10 concentrations were significantly lower in the summer than winter.•Minimum and average PM 2.5 and PM10 concentrations differed significantly throughout the day.•This data could influence racehorse management decisions and have implications for human caretakers working in stables. Despite their implication in the pathogenesis of lower airway inflammation, limited baseline data exists for airborne particulates in Thoroughbred racehorse stalls in the United Kingdom. This study documents airborne particulate size and concentrations in Newmarket training yards using a nephelometer (DustTrak DRX 8534, TSI). Each stall was sampled on a summer and winter day at three time points (morning, midday and evening). Minimum, mean and maximum/min ranges were calculated for the fraction of particulates with an aerodynamic diameter smaller than 2.5 μm (particulate matter (PM) 2.5) and 10 μm (PM10). Comparisons were made using Wilcoxon signed-rank test. Average particulate concentration ranges were 0.02−0.27 (summer) mg/m3, 0.01−0.37 (winter) mg/m3 for PM2.5 and 0.02−0.39 (summer) mg/m3, 0.02−0.60 (winter) mg/m3 for PM10. Statistically significant effects of season and time of day were established, resulting in implications for future studies investigating the effect of yard variables on airborne particulates.