The instrumented street

01Field scene

The street is already an instrument platform.

Street poles stand every few dozen metres, have power, and sit at the height where people breathe. A small cell at eight metres adds radio capacity where the macro network runs out, and the same pole can carry particulate, nitrogen dioxide and temperature sensors.

The sensors are not the system. The system is the chain that turns a low-cost reading into a value someone can act on: calibration against a reference station, a timestamp, a published correction, and a record of where each number came from.

Figure as text: Four blocks with small cells, sensors and an edge node

A wireframe city block of nine buildings. Three street poles carry small cells, two carry air-quality nodes and one a heat sensor; dashed red links run from each to an edge node at the corner.

• Small cell, 8 m
• Air quality
• Heat
• Edge node

02Simulator

How far one small cell reaches.

Small cells are sized by the link budget, not by the map. At 3.5 GHz in a street canyon, path loss rises faster than in free space, and the cell radius closes at a few hundred metres. Change the frequency, the power or the path-loss exponent and see how many sites a hundred square kilometres need².

The radio horizon of a mast eight metres high is far larger than the range the budget allows, so in a city the budget, not the curvature of the Earth, sets the spacing³.

Figure as text: Small-cell radius from the link budget

A plan drawing of one site with three circles: the range the budget closes, the radio horizon, and the usable cell radius in red.

03Data story

What the air-quality nodes are measured against.

The World Health Organization’s 2021 guidelines set an annual mean of 5 µg/m³ for fine particulate matter and 10 µg/m³ for nitrogen dioxide⁴. The European Union’s revised directive sets binding limits for 2030 at twice those values, a step toward the guidelines rather than an arrival⁵.

Low-cost sensors drift with humidity and temperature. A published performance protocol for sensor systems is what lets a city compare one deployment with another⁶.

Figure as text: Guideline values and 2030 limits for two pollutants

A bar chart of six values in micrograms per cubic metre: the WHO 2021 guidelines for PM2.5 and nitrogen dioxide, annual and 24-hour, and the EU limits that apply from 2030.

04Timeline to 2030

Toward 2030 on one street.

The horizon for the street is set by documents that already exist: the health guidelines, the sensor protocol, the 2030 limits and the urban goal of the 2030 Agenda⁷. Each changes what a city must measure, how well, and how openly.

Figure as text: Air quality on the street, 2015 to 2030

A timeline from 2015 to 2030 in three lanes: health guidelines, law and measurement method.

1. 2015-09 Sustainable Development Goal 11 adopted. Target 11.6 asks cities to reduce the adverse environmental impact per person, with attention to air quality, by 2030.⁷
2. 2021 Performance protocol for gas sensor systems (CEN/TS 17660-1). A shared test for low-cost sensor systems in ambient air.⁶
3. 2021-09 WHO air quality guidelines revised (WHO AQG 2021). Annual guideline for PM2.5 lowered to 5 µg/m³ and for NO₂ to 10 µg/m³.⁴
4. 2024-11 EU ambient air directive revised (Directive (EU) 2024/2881). New limit values, to be met by 2030, and more monitoring points where people live.⁵
5. 2030 EU 2030 limits apply. PM2.5 annual mean 10 µg/m³, NO₂ annual mean 20 µg/m³.⁵