What about the roadside API?

Apart from reporting the general air pollution index, we also set up 3 roadside stations for monitoring air quality at street level in urban areas. The 3 monitoring stations are located at the kerb of roads with heavy traffic in Causeway Bay, Mong Kok and Central. As these roadside stations are close to vehicle exhaust emissions, the API they measured will therefore be higher than the general API.

For most people, the roadside API is less relevant as they spend only a short period of time each day at such locations. The roadside API is of more interest to those who spend several hours continuously each day in busy streets.