Breathe Better. Live Smarter.^®

Know what you’re measuring.

Explore the sensors, accuracy, and sources behind Terrestream’s readings.

Talk to sales Download datasheet

SEN66 BMP390L OPT3001 Manufacturer sources

From sensor to insight

Sensirion SEN66

CO₂ · Particles · Temperature · Humidity
VOC Index · NOₓ Index

Bosch BMP390L

Barometric pressure

Texas Instruments OPT3001

Ambient light

11Sensor-derived readings

IAQCalculated air quality index

Terrestream Intelligence

Indoor readings and outdoor context, connected to useful recommendations.

Measured. Indexed. Documented.

Evidence behind each signal

See which readings come from sensors, which track relative changes, and which Terrestream calculates.

CO₂measured
IAQderived
VOC Indexindexed
NOₓ Indexindexed
PM1.0measured
PM2.5measured
PM4.0measured
PM10measured
Temperaturemeasured
Humiditymeasured
Pressurecontext
Lightcontext

Sensor specifications support evaluation. They do not certify a building or establish code compliance.

Air-quality evidence and confidence documentation

Published specifications

Follow the sources behind each sensing component and its capabilities.

Ventilation standards and monitoring workflow reference

Building standards

Understand what the sensor supports and what a building project still needs to verify.

CO2 trace 420 ppm Good

Core sensing

Six sensors. Twelve signals.

Track particles, gases, and room conditions together. Pressure and light add context; Terrestream calculates the overall IAQ index.

VOC Index and NOx Index are index outputs, not laboratory TVOC or regulatory NO2 measurements. SEN66 product page

Terrestream signals

Eleven sensor-derived readings plus Terrestream IAQ, produced from six sensing functions in one device.

View source ↗

CO₂ accuracy range

400–5,000 ppm

The SEN66 datasheet specifies CO2 accuracy from 400 to 5,000 ppm, starting at +/-(50 ppm + 2.5%) at 400-1,000 ppm, after 2 days of operation that include fresh air and with fresh air at least weekly.

View source ↗

PM mass range

0–1,000 µg/m³

Datasheet mass-concentration capability for PM channels.

View source ↗

VOC / NOₓ Index

1–500

Index outputs for relative gas events, not laboratory TVOC or regulatory NO2 concentration.

Intelligence

Indoor and outdoor evidence

Switch between the flow and radial views to inspect which measured and contextual inputs support each interpretation.

Weather, air quality, pollen, and smoke data come from Open-Meteo, Google, NOAA, and NASA.

Indoor (your device) Outdoor (open data) Analysis Output

Swipe or use the arrow keys to explore the full chart.

See it in the dashboard & app

Clear measurement limits

Understand what a reading can tell you

Readings show changes in your room. Understanding how they are produced helps you interpret those changes.

Particles, by size

Optical sensing estimates particle mass. It does not identify the material.

Gas changes, over time

VOC and NOₓ indices track relative changes, not individual gas concentrations.

Conditions matter

Humidity, particle composition, and placement can affect a reading.

Measurement specification VOC Index source

Explore measurement limits and example charts

PM size cascade

datasheet capability

PM1.0, PM2.5, PM4.0, and PM10 are size-bucketed mass concentration outputs, not direct chemical identification.

PM SPC precision check

datasheet capability

control band = mean +/- k*sigmaSPC framing makes repeatability visible: the mean, warning band, and control limits stay separate from field accuracy claims.

Sensirion's specification statement distinguishes calibration precision from accuracy and explains why aerosol-specific correction may be needed outside the calibration envelope. specification statement

VOC / NOx index fingerprint

example event pattern

These example values show relative changes. The labels remain VOC Index and NOx Index because the sensor does not identify individual gases.

CO2 ventilation decay

example ventilation pattern

C(t) = C_out + (C₀ - C_out)e^-ACH*tVentilation recovery is evaluated by curve shape and decay rate, not only by a single peak ppm value.

The chart demonstrates a ventilation pattern. The SEN66 datasheet supports the stated CO2 range and accuracy limits.

How readings are calculated

Look inside the calculations

Explore worked examples for particles, light, and ventilation, with the assumptions and sources alongside.

Particle measurement source Light sensor source

Explore formulas and worked examples

Particle-count penalty

Sensirion source figure

N_relative = (10 / d)³At equal mass, smaller particles appear far more often in the optical sample volume than coarse particles.

PM precision check

Mean plus/minus 2 sigma is the acceptance frame.

typical deviation = μ ± 2σ

At μ = 250 ug/m3, a +/-10% high-range envelope means the typical deviation band should fit inside 225-275 ug/m3.

source

Aerosol statistics

Particle count changes with diameter cubed.

relative count ∝ mass / diameter³

At the same mass concentration, 10 um particles are about 1,000x fewer than 1 um particles, which is why coarse-particle precision is harder.

source

OPT3001 lux decode

The digital register resolves to lux through exponent and result.

lux = 0.01 × 2^E × R

Example: E = 8 and R = 250 gives 0.01 x 256 x 250 = 640 lux.

source

Ventilation decay

Recovery is exponential, so slope matters.

C(t) = C_out + (C₀ - C_out)e^-ACH·t

Example calculation: 1,400 ppm decaying toward 420 ppm at 3 ACH for 20 minutes lands near 781 ppm.

example calculation

RESET / WELL VOC pathway

When a VOC index needs more context

Terrestream reports relative gas changes as VOC Index. Sensirion also documents a laboratory conversion method for specific building-standard workflows.

This is a controlled-laboratory method, not a general field conversion or a certification.

Sensirion standards note

Explore the laboratory method and standards requirements

VOC Index to TVOC equivalents

vendor formula recreation

Sensirion states the VOC Index to TVOC procedure is valid under laboratory conditions and recommends building-standard tuning parameters, including a 720 h normal learning time offset. Sensirion VOC standards note

Step 1

VOC Index to ethanol equivalent

TVOC_ethanol=(ln(501 - VOCIndex) - 6.24)×-381.97

Step 2

WELL Mølhave equivalent

TVOC_Mølhave=(ln(501 - VOCIndex) - 6.24)×-996.94

Step 3

RESET isobutylene equivalent

TVOC_isobutylene=(ln(501 - VOCIndex) - 6.24)×-878.53

Boundary

Designed to support standards-aware workflows

Project certification still requires accepted installation, reporting, calibration governance, and the relevant accrediting or project-review process.

WELL accuracy envelope

Sensirion standards note

Sensirion describes WELL's continuously monitoring sensor accuracy envelope as +/-20 ug/m3 plus 15% of measured value and reports its VOC-sensor behavior inside that envelope in the note. accuracy source

Index outputs are still indexes

limitation note

VOC IndexRelative gas-event signal and trend output. Use TVOC only inside the Sensirion conversion workflow.
NOx IndexCombustion and oxidizing-gas context. It is not a regulatory NO2 concentration analyzer.
TVOC pathwayUseful for standards-aligned workflows when assumptions, tuning, and governance are documented.

VOC Index note NOx Index note

Context evidence

Pressure and light add context

Bosch BMP390L

pressure context

Pressure adds context for weather changes and airflow around a building.

Range, accuracy, and source

Pressure helps with weather, infiltration, HVAC, and placement diagnostics. Bosch lists 300-1250 hPa operation, typical absolute pressure accuracy of +/-0.50 hPa, and typical relative pressure accuracy of +/-0.03 hPa. Bosch source

Texas Instruments OPT3001

visible-light context

Ambient light helps the display respond to the room’s brightness.

Light response, calculation, and source

lux = 0.01 x 2^E x RThe OPT3001 register format uses exponent and result fields to cover dim rooms and bright daylight without manual range switching.

Lux helps with visible-light environment and display adaptation. TI specifies 0.01 lux to 83k lux measurements, automatic full-scale ranging, photopic response matching, and typical IR rejection greater than 99%. TI source

From readings to building decisions

Evidence for building decisions

Ventilation

Meeting-room CO2

See buildup and ventilation decay so facilities teams can tune schedules, damper logic, or room-use guidance.

CO2 + decay

Source ID

Cooking and combustion separation

Correlate PM, VOC Index, and NOx Index instead of treating every spike as the same event.

PM + VOC + NOx

Recovery

Filtration recovery

Watch PM recovery time after an event and compare rooms, filters, and purifier placement.

PM slope

Envelope

Infiltration context

Use pressure and outdoor conditions to explain why outside air is helping, hurting, or simply not moving.

Pressure + weather

Terrestream Facilities product preview showing example Room 214 history falling from 63°F to 48°F. — Product preview · Example data Release-candidate Facilities view, not a customer deployment.

Portfolio

Fleet maintenance

Surface stuck baselines, placement problems, and rooms that keep producing the same source pattern.

Outliers + baselines

Breathe Better. Live Smarter.

Put better measurements to work.

One device. Twelve signals. Useful guidance for the spaces you care about.

$249 USD one-time

Order yours

Setup Datasheet Compliance

No subscription required
30-day returns
1-year limited warranty
Fast shipping via FedEx

Six sensors. Twelve signals.

Built on genuine Sensirion, Bosch, and Texas Instruments sensors.

CO₂
IAQ
VOC
NOₓ
PM1.0
PM2.5
PM4.0
PM10
Temperature
Humidity
Pressure
Light

Included

In the box: the sensor, a 6 ft (1.8 m) USB-C cable, a power adapter and a printed guide
Free apps, web dashboard and account
Privacy-first air data