BMI is measuring airborne particulate pollutant concentrations in the outside air at its location in Hayward, CA. From the measurements we calculate the total particulate mass loading - which can be compared with the EPA 24-hour standard of 65 micrograms/cubic meter and the one-year-average standard of 15 micrograms/cubic meter. Check out the latest pollution observations here.

Currently, a BMI differential mobility analyzer, together with a condensation particle counter, is used to observe the number concentration of particles over the 0.03 to 1 micrometer diameter size range. The particle sample is dried before the measurement to remove any particle-bound water from the aerosol that would influence the sizing. The number concentration data may be converted to particulate mass using an assumed aerosol density (1.6 g/cc in this case). The measurements are made on air sampled through an inlet system that protrudes 10 ft above the roof of our building, within a few hundred feet of a major freeway (Hwy 880) and within 30 feet of an industrial expressway. Numerous diesel trucks and other large point pollution sources are located nearby and upwind of BMI. The measurements are performed once every minute with about 30 seconds in between measurements to process data and post the data to our website.

By summing the number of particles observed at each size over the entire size range, a total number concentration of aerosol per cubic centimeter of air is calculated. Similar calculations are performed to determine total aerosol surface area, volume and mass concentrations. The values for the last set of measurements is shown in the image below. The displayed measurement results will update roughly every 3 minutes when the measurement systems at BMI are operating. For reference, the U.S. EPA standard for exposure to fine particulate matter smaller than 2.5 micrometer diameter is 65 micrograms per cubic meter (24 hr average). The one-year standard is 15 micrograms per cubic meter. EPA is considering reducing the 24 hour average standard to 35 micrograms per cubic meter. Mass values shown in the plot below are in units of micrograms per cubic meter.

A timeline of calculated mass concentrations for particles smaller than 1 micrometer is also shown in the plotted results. These masses are calculated from the observed aerosol volume and assuming an average particle density of 1.6 g/cc. Actual chemical composition measurements would be necessary to establish the correct density to be used to determine the airborne mass concentrations. The reported time and date on the plot are shown as 'UTC' (Coordinated Universal Time), which is the time at the Greenwich Meridian (ie London, England). Subtract 8 hrs from the times shown to adjust to local California time. In the future we may be able to provide this information.

These data are provided to the general public for information purposes only, and represent non-quality-controlled results that still require final processing. Please do not quote or cite these results without first speaking to Dr. Fred Brechtel (fredj@brechtel.com).