PM Monitoring

NHDES has monitored particulate matter since 1967. Over the years, monitoring efforts have focused on different sized particles and incorporated different methods of measurement. NHDES currently monitors PM10 at three locations and PM2.5 at seven locations throughout the state (see map below). Please visit Air Quality Monitoring and Data for more about air quality monitoring in New Hampshire.

map of particulate matter monitoring stations in new hampshire

photo of the NHDES air monitoring station in Keene
NHDES Air Monitoring Station in Keene, NH

Monitoring by Particle Size
Early particulate matter monitoring from 1967 to 1987 focused on total suspended particles (TSP, all particle sizes). As research revealed that the worst health effects result from the smallest particles, monitoring efforts shifted from TSP to PM10 and PM2.5. NHDES established an extensive monitoring network for PM2.5 beginning in 1998.

Filter-based Monitoring
Initially, the only method available for measuring particles was a filter-based method. A technician set up a filter, allowed it to collect particles for 24 hours, picked up the filter when sampling was complete, and shipped it to a laboratory for analysis. This provided a day’s average

photo of clean and dirty PM filters
Clean (left) and dirty (right) PM filters: a filter like this collects particles in the air stream for 24 hours.

concentration, but the results were not available from the lab for weeks to months after the sampling day. Moreover, because of the time needed to set up and remove the filters, NHDES would only run the filters once every few days.

Hourly Monitoring
Advances in technology have created significant changes in particulate matter monitoring. Today, NHDES uses the filter method along with new instrumentation capable of measuring particulate matter on an hourly basis. The newer method provides hourly measurements of particle concentration every day of the year. Automated computer systems continuously transmit these data to NHDES computers and websites for real-time viewing and analyses. NHDES uses an instrument called a Beta Attenuation Monitor (BAM) to measure hourly PM2.5 concentration at five sites: Keene, Londonderry, Portsmouth, Lebanon and the summit of Pack Monadnock in Peterborough.

photo of the BAM particulate matter monitor

photo of the sampling tape from a BAM monitor
BAM (left) and BAM Sampling Tape (above): The BAM monitors particulate matter every hour; each circle on the sampling tape represents an hour of particle collection.