The below graph shown the real-time NO2 (nitrogen dioxide) concentration of an office selected in Sai Ying Pun. This is a pilot project with Arduino-based platform measuring air quality using micro-sensors. (下圖為香港西營盤某辦公室實時量度的二氧化氮濃度)
You can compare it with the NO2 concentration recorded at official Environmental Protection Department (EPD) website in Hong Kong, in Central/Western District (Sorry I have no idea how to get real-time data from EPD on web and embed onto my website.
You can see there is a huge discrepancy between the readings – one major reason is that the EPD readings are taken from stations way above the ground (16 meters) and does not represent the true concentration we are breathing at ground level.
This is how the sensor looks like.