How to Be a Pollution Watchdog in Your Community

When government air quality monitoring fails to capture what a community is actually breathing — because the nearest regulatory monitor is miles away, or because monitoring is averaged in ways that obscure local hotspots — low-cost sensors and community monitoring networks can fill the gap.

The past decade has seen the development of increasingly capable low-cost air quality sensors — particularly for PM2.5, NO₂, and ozone — that have enabled communities to document air quality conditions that official monitoring missed. The PurpleAir network has deployed thousands of low-cost PM2.5 sensors globally, creating a real-time air quality map of far greater spatial density than the regulatory monitoring network. Communities in Louisiana's Cancer Alley, near refineries in Richmond, California, and adjacent to industrial facilities across the country have deployed sensor networks that have documented pollution events that regulatory data would not have captured.

Understanding how to use these tools — their capabilities, their limitations, and how to deploy them for maximum community benefit — is the foundation of citizen science air quality monitoring.

Low-cost PM2.5 sensors — PurpleAir being the most widely deployed — use optical particle counters to estimate particle concentrations from light scattering. They are not regulatory-grade instruments; they require calibration and their accuracy depends on environmental conditions (humidity significantly affects readings). But they provide real-time, spatially dense data that regulatory monitoring cannot match.

How to use PurpleAir data reliably: • Use the EPA's correction factor for PurpleAir data: the EPA has developed a correction algorithm (the US-wide correction) that significantly improves PurpleAir accuracy relative to regulatory monitors. Many platforms including AirNow display PurpleAir data with this correction applied. • Compare to the nearest regulatory monitor: when your local PurpleAir sensor is close to a regulatory monitor, comparing the two over time calibrates your confidence in the sensor's readings • Identify patterns rather than point values: low-cost sensors are most useful for detecting events (sharp increases correlating with industrial operations or traffic patterns) rather than for absolute concentration accuracy • Use multiple sensors: deploying 3–5 sensors in a community and comparing readings across sensors helps identify when a single sensor is malfunctioning

The TRI database for community emissions research: As described in the TRI article, the EPA's TRI Explorer at epa.gov/triexplorer allows ZIP-code-level searching for all reported releases. Combining TRI data with sensor data — asking whether sensor readings correlate with known emission sources — is the foundation of community emissions investigation.

When air quality monitoring data documents a potential violation or when environmental conditions suggest unreported releases, the EPA's complaint process provides a pathway for formal investigation.

EPA Region complaint filing: The EPA is divided into 10 regional offices, each covering specific states. Complaints about air quality violations, unpermitted releases, or significant community impacts can be filed with the relevant regional office. The EPA's website provides region-specific contact information and complaint intake forms.

What makes a complaint effective: • Specific dates and times of observed events • Air quality sensor data if available, with sensor location and data download • Documentation of odour, visible plumes, or physical symptoms correlated with events • Information about the facility believed responsible and its permit status • Community health data if available (clinic visit records, self-reported symptom surveys)

State environmental agency complaints: State agencies often have more direct enforcement authority over permitted facilities within their jurisdiction. State complaint processes are often faster than federal processes for locally regulated facilities.

The community health survey Systematic community health surveys — door-to-door or online — that document symptom patterns, timing, and geographic distribution can provide epidemiological data that complements air quality monitoring. Academic partners (many universities have environmental health or public health programmes that work with community groups) can provide methodological support and credibility for health survey data.

The most impactful community monitoring programmes combine technical rigor, strategic deployment, and community organising — turning data into documented evidence that regulatory agencies and courts can act on.

Designing a community sensor network:

Sensor placement strategy Place sensors to address specific questions: What are concentrations near the fence line of the facility of concern versus at the community centre versus at the school? How do concentrations vary by wind direction? What is the relationship between facility operating schedules and community air quality events?

Data management Raw sensor data needs to be downloaded, QA/QC checked, and stored in a format that can be analysed and shared. Several tools exist for low-cost sensor data management, including the South Coast AQMD's AQ-SPEC programme and PurpleAir's own data download capabilities.

Building the case The goal of community monitoring is often to build a documented record that can support regulatory complaints, permit challenges, or environmental justice claims. This requires: • Consistent long-term monitoring (weeks to months) to establish baseline and event patterns • Correlation analysis with facility operations, wind data, and TRI-reported releases • Connection to community health data documenting that sensor-measured pollution events coincide with health symptoms

Academic and legal partnerships Environmental law clinics at law schools, academic environmental health researchers, and environmental justice organisations like Earthjustice and the Center for Health, Environment & Justice can provide the legal and technical support that transforms community monitoring data into actionable regulatory or legal strategies.

PollutionProfile's community-level air quality data integration draws on the same sensor networks and regulatory monitoring data that underpin community monitoring programmes — providing users with the local context to understand how their immediate environment relates to the broader community air quality picture.