Membrapor has further improved the highly selective NO2/CA-2 sensor for NO2 air quality measurements. The sensitivity could be almost doubled, allowing resolution of even lower concentrations in the ppb range. The sensor incorporates the proven catalytic O3 filter, which eliminates the otherwise typical O3 cross-sensitivity of electrochemical NO2 sensors. In addition, the NO2/CA-20 sensor is now available for measuring ranges up to 20 ppm.