Effectiveness of portable HEPA air cleaners on reducing indoor PM2.5 and NH3 in an agricultural cohort of children with asthma: A randomized intervention trial

Abstract

We conducted a randomized trial of portable HEPA air cleaners with pre-filters designed to also reduce NH₃ in non-smoking homes of children age 6-12 with asthma in Yakima Valley (Washington, USA). Participants were recruited through the Yakima Valley Farm Workers Clinic asthma education program. All participants received education on home triggers while intervention families additionally received two HEPA cleaners (child's sleeping area, main living area). Fourteen-day integrated samples of PM_2.5 and NH₃ were measured at baseline and one-year follow-up. We fit ANCOVA models to compare follow-up concentrations in HEPA vs control homes, adjusting for baseline concentrations. Seventy-one households (36 HEPA, 35 control) completed the study. Most were single-family homes, with electric heat and stove, A/C, dogs/cats, and mean (SD) 5.3 (1.8) occupants. In the sleeping area, baseline geometric mean (GSD) PM_2.5 was 10.7 (2.3) μg/m³ (HEPA) vs 11.2 (1.9) μg/m³ (control); in the living area, it was 12.5 (2.3) μg/m³ (HEPA) vs 13.6 (1.9) μg/m³ (control). Baseline sleeping area NH₃ was 62.4 (1.6) μg/m³ (HEPA) vs 65.2 (1.8) μg/m³ (control). At follow-up, HEPA families had 60% (95% CI, 41%-72%; p < .0001) and 42% (19%-58%; p = .002) lower sleeping and living area PM_2.5 , respectively, consistent with prior studies. NH₃ reductions were not observed.

Keywords: HEPA cleaners; NH3; PM2.5; asthma; children; randomized trial.

FIGURE 1

Scatter plots of baseline vs follow-up PM_2.5 in the child’s sleeping area (A) and main living area (B). Fitted lines represent the ANCOVA model equations for the HEPA (darker line) and control (lighter line) groups; the vertical difference between lines represents the intervention effect in the sleeping area (A: exp(−0.91) = 0.40, or 40%) and living area (1: exp(−0.54) = 0.58, or 58%); note that the axes are logarithmically scaled to correspond with the statistical analysis of log concentrations. Sample sizes: sleeping area (A) N = 35 HEPA, N = 33 control; living area (B) N = 34 HEPA, N = 33 control

FIGURE 2

Scatter plot of baseline vs follow-up NH₃ in the child’s sleeping area. Fitted lines represent the ANCOVA model equations for the HEPA (darker line) and control (lighter line) groups; the vertical difference between lines represents the intervention effect (exp(0.15) = 1.16, or 116%); dotted gray lines indicate upper limit of quantitation (ULOQ) (285 ppb, or ~ 198 μg/m³ at the average temperature of each home); note that the axes are logarithmically scaled to correspond with the statistical analysis of log concentrations. Sample sizes: N = 36 HEPA, N = 35 control