Smarter Monitoring Delivers Healthier Air for Milpitas

In Milpitas, California, residents living near industrial operations raised persistent odor concerns. The Bay Area Air Quality Management District (BAAQMD) recorded more than 1,200 complaints annually, signaling a growing need for clarity on where odors originated to mitigate the root cause and improve quality of life for residents.

Traditional odor investigations, including nasal ranger surveys, confirmed that an odor was present, but they struggled to pinpoint the precise source. Results produced broad representation of odor presence, showing where odors were detected without providing defensible attribution or chemical makeup.

Onterris worked alongside local stakeholders to shift the conversation from general odor concerns to a clearer understanding of what was in the air, where it was coming from, and what actions could be taken.

Onterris deployed the PTR Van, a mobile lab equipped with a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), to measure volatile organic compounds (VOCs) in real time and at trace levels, enabling compound-level fingerprints across overlapping sources.

Because the lab is mobile, the team could move quickly across neighborhoods and potential source areas, capturing changing conditions as winds shifted and operations varied throughout the day. Integrated GPS and meteorological sensors connected concentration data to time, location and wind patterns, producing high-resolution plume mapping that decision-makers could use.

The investigation focused on four likely contributors: a large landfill, a food waste composting facility, a wastewater treatment plant processing 110 million gallons daily and a nearby natural estuary with potential sulfurous gas releases.

Onterris collected more than 40 stationary samples from specific processes inside each facility and completed 13 mobile sampling runs throughout Milpitas.

Collecting measurements is only useful if the analysis can separate overlapping signatures. Onterris applied Principal Component Analysis (PCA) to distinguish patterns in the VOC data and build distinct odor fingerprints for each source area.

That approach did more than validate the initial list, it revealed an additional contributor: an estuary drainage pipe releasing sulfurous compounds into nearby neighborhoods under certain conditions. That data allowed for targeted mitigation that would have otherwise gone undetected.

The models attributed 43% of odor complaints to the landfill, with other facilities contributing distinct signatures as well. With timing and chemical fingerprints, operators could make operational adjustments to the processes most associated with odor impacts.

This created a repeatable and proactive way to manage odor complaints. Instead of treating complaints as isolated events, teams could compare new reports to established baselines, respond with targeted operational adjustments and communicate progress with greater transparency.

The Milpitas project shows why mobile lab technology is becoming the future of odor investigations. It deploys quickly, scales across multiple sites and produces scientifically grounded evidence that links odors to the root cause. This approach is particularly effective in complex industrial corridors, where odors may stem from multiple co-located sources such as landfills, wastewater systems and manufacturing facilities and cannot be reliably attributed to a single source.

When decision-makers can see a defined odor fingerprint rather than a generalized indication of odor presence, they can act with precision, document progress and sustain community trust over time.