Evaluation of environmental beta attenuation monitor (EBAM) performance in low PM2.5 concentrations and higher relative humidity environment: expectations, data utility, and considerations for wildland fire smoke uses
| Authors: | Susan O'Neill |
| Year: | 2026 |
| Type: | General Technical Report |
| Station: | Pacific Northwest Research Station |
| DOI: | https://doi.org/10.2737/pnw-gtr-1047 |
| Source: | Gen. Tech. Rep. PNW-GTR-1047. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 38 p. (Online Only). |
Abstract
Environmental beta attenuation monitors (EBAMs) are commonly used to measure 1-hour average particulate matter concentrations in smoke from prescribed fires and wildfires. Because relative humidity (RH) can artificially inflate particulate matter concentrations, EBAMs are equipped with an internal heater that activates when ambient RH reaches a specified setpoint. Most studies address high PM2.5 concentration conditions, where the EBAM is well documented to perform quite well on an hourly basis (R2 of 0.95). In prescribed fire applications, however, increases in PM2.5 concentrations are often more subtle than those observed during wildfires, and several studies have reported that 1-hour EBAM measurements can be noisy under clean, low-PM2.5 conditions, limiting data usability. These studies, however, do not clearly illustrate what noisy data means or show what a user can expect when viewing data on an hourly basis. These factors highlight the need to better understand EBAM performance under conditions of low PM2.5 concentrations and elevated RH and to identify optimal operating settings for these environments.
To address these needs, we evaluated EBAM performance by colocating four EBAMs with one federal reference method (FRM) sampler and one federal equivalent method (FEM) monitor. Specifically, we examined two internal heater settings (15- and 45-percent RH setpoints) for two models of EBAMs—two EBAM-V1s (EBAM version 1, an older model) and two EBAM-WFs (EBAM wildfire, a new model). Hourly EBAM measurements exhibited substantial variability, and error (defined as the difference between EBAM and FEM measurements) occasionally exceeded 10 to 20 μg/m3 under clean atmospheric conditions, particularly for the EBAM-V1 operated at the 45-percent RH setpoint. Overall, the EBAM-WF configured with the 15-percent RH setpoint demonstrated the best performance, with R2 values of 0.73 for 1-hour average PM2.5 concentrations and 0.99 for 24-hour average PM2.5 concentrations. Although the 15-percent RH setpoint produced a slight low bias (mean bias of −1.3 μg/m3), it was the most effective configuration for reducing hour-to-hour absolute error relative to the FEM monitor.