Prototype of a spectroscopic sensor for accurate, real time monitoring of personal exposure to nitrogen dioxide

Nitrogen dioxide (NO₂) is one of the most serious air pollutants, producing health outcomes that include increased risks of cardiovascular mortality, lung cancer, and a 50% increased likelihood of children developing asthma. Expanding the scope and range of NO₂ measurements is therefore desirable to quantify NO₂ levels and emissions in different settings. However, current research and regulatory instruments are too expensive for widespread deployment and too bulky for personal exposure measurements, while low cost sensors do not have the required sensitivity, accuracy, and response time for many applications.

Here we describe an approach to develop a spectroscopic sensor for NO₂ based on the differential absorption of NO₂ at two nearby wavelengths. A single light source is used to reduce the effect of light source intensity fluctuations. Early results of the sensor performance in an optical cavity arrangement for in situ measurements are presented. We report the Allan deviation of the system and compare the sensor response against a chemiluminescent instrument in an atmospheric simulation chamber. The sensor’s sensitivity to potential interferences (aerosols, glyoxal and methylglyoxal, water vapour) is presented. Results from optimising signal detection and strategies to improve instrument performance are also discussed.

The approach is expected to pave the way for a relatively low-cost, portable and robust NO₂ sensor that can be configured for remote sensing or in situ monitoring to quantify air quality. Target applications include measurements across towns and roads, and outside schools.