Many optical dust monitors are calibrated using reference test dusts such as Arizona Road Dust (ISO 12103-1). These standards give repeatable responses in the lab, but site dusts vary widely in composition, shape and refractive index. Without sensible verification, readings can drift from reality.

What Arizona Road Dust is (and is not)

It is a manufactured reference with defined size ranges used for factory calibration and comparison. It is not a guarantee your instrument will read perfectly for silica, wood, or welding fume. Expect bias if your site aerosol differs significantly from the reference.

Build a practical calibration routine

Start each shift with a zero check (use the instrument’s zero filter or clean HEPA air) and verify flow where applicable. Keep firmware updated and follow the maker’s service intervals. Record checks in a log so you can defend the data.

Site-specific adjustment

When decisions depend on accuracy, co-locate an optical monitor with a gravimetric sampler for a task period and derive a site factor. Repeat if materials or processes change. Note humidity and temperature, which can influence optical readings. Do not apply factors from other sites without validation.

Interpreting numbers sensibly

Use monitors for trends and alarms; use gravimetric samples for compliance-grade confirmation under COSHH. If readings climb, act on controls rather than debating fine calibration points: improve source capture, increase under-load airflow on air cleaners, and fix housekeeping.

Practical takeaways

• Factory calibration with Arizona Road Dust is a starting point, not the finish line.
• Perform routine zero/flow checks and keep a calibration log.
• Validate with co-located gravimetric sampling when accuracy matters.
• Use site-specific factors and revisit them when processes change.
• Prioritise controls based on trends while you confirm precise values.

This approach keeps monitoring credible and decision-focused without overcomplicating day-to-day work.