Air quality sensor

Air quality sensor comprises an optical particle sensor and a programmable processor circuit. The optical particle sensor detects particles having a size of 10 microns or less in diameter in ambient air of the optical particle sensor. The programmable processor circuit continuously computes updated air quality measures for the ambient air using an estimation algorithm based on pulses in an output signal from the particle sensor over time, such as a cumulative particle density value and/or a cumulative particle weight value. The optical particle sensor may comprise a LED and accordingly detect particles based on reflection of light energy from the LED by particles in a chamber of the sensor.