Sofia City Air Quality Monitoring Volunteer Network
Sofia City Air Quality Map
A network of interconnected backbone sensor nodes, spread across Sofia, measuring temperature, relative humidity, a set of Volatile Organic Compounds and an Air Quality Index, assisted by an ever-growing net of additional volunteer provided sensors, resulting in increased accuracy of our main backbone nodes, expanding their reach and usefulness. The information is collected and displayed here - openly, in service of the community.
Our network is built on the principles of accuracy footprint expansion by data aggregation. The main components are the backbone nodes. They encompass their own set of sensors, stable power and Ethernet connection, a LoRa radio modem.
Their accuracy and footprint are traditionally limited by the reach of their sensors, only displaying a local unaveraged value. This limitation is overcome by providing a clear and simple way for volunteers to send data to those backbone nodes by their own sensors, all located within 1-2km from the backbone node. This information is than averaged with our own sensors, providing a more complete and clear view of the area. Than the backbone data is carried via Ethernet to a collector, and shared with you through this page.
There is no fee, no contract and no subscription. Just people caring for other people.
How the network works
Humidity
Temperature
tVOC eCO2
Humidity
Temperature
tVOC eCO2
LoRa Radio provides simple, secure, robust and proven way of connecting volunteers to the network.
Ethernet connections provide
robust backbone connectivity.
An ever-growing volunteer provided sensors provide increased accuracy to our main backbone sensor nodes, expanding their reach and usefulness
Our network is based on multiple sensors, whose data is collected by backbone nodes and shared with you via a webpage.
Our Sensors
Relative humidity (RH)
0-100%
Air temperature
-20°C ~ 65°C
Accuracy
+/-2% of reading from 5–95% RH
tVOC (total VOCs)
0-65000ppb
eCO2 (equivalent CO2)
400-65000ppm
AQI Air Quality Index
1 (best) - 5 (worse)
Accuracy
1ppb/1ppm
LoRa gives a simple, secure, robust and proven way of connecting volunteers to the network: kilometres of range on a fraction of a watt of power, across neighbourhoods, with minimum and very economic personal expense, allowing more people to join. Each node carries two combined measurement instruments: one for temperature and humidity, and the other for the organic compounds, dissolved in it. Both are filly digital and factory-calibrated.
A word on the numbers:
The Total Volatile Organic Compounds encompass a wide range of volatile organic compounds (VOCs) including ethanol, toluene, hydrogen and oxidizing gases, higly charged ozone and many others, generated by both natural (ligtning storms for example) and human (production and transportation exhaust, fires, solvents, cleaning products, etc.) activity. Their median is detected and aggregated, giving the TrueVOC or TVOC level you see on our map. Based on this measurement an Equivalent CO2 level is calculated and estimated from the VOC signal, giving a median idea of how stale the air might have become, in circumstances like temperature inversions with windless weather, for example. Our tVOC sensors have smart algorithms, that calculate CO2-equivalents, TVOC, air quality indices (AQIs) and perform humidity and temperature compensation, as well as baseline management.
Info and links
Air Quality / Normative Acts
Air Quality Laws
| AQI-UBA | Hygienic Rating | Recommendation | Exposure Limit | |
|---|---|---|---|---|
| # | Rating | |||
| 5 | Unhealthy | Situation not acceptable | Use only if unavoidable Intensified ventilation recommended | Hours |
| 4 | Poor | Major objections | Intensified ventilation recommended Search for sources | <1 month |
| 3 | Moderate | Some objections | Increased ventilation recommended Search for sources | <12 months |
| 2 | Good | No relevant objections | Sufficient ventilation recommended | No limit |
| 1 | Excellent | No objections | Target | No limit |
| Output | Air stale-ness | |
|---|---|---|
| eCO2 / CO2 ppm | Rating | |
| >1500 | Bad | Dangerously stale |
| 1000 – 1500 | Poor | Very stale |
| 800 – 1000 | Fair | Stale |
| 600 – 800 | Good | Average |
| 400 – 600 | Excellent | Target |