Combining passive sampling and digital imaging to measure light-absorbing aerosols

Abstract:

We present an ultra-low-cost passive sampler (materials cost ~10 USD), suitable for measuring long-term average levels of light-absorbing aerosols in heavily polluted indoor/near-outdoor environments. For those conditions, conventional active sampling methods tend to saturate. Our sampler involves a paper filter housed in a 3D printed plastic case; particles passively deposit on the filter paper via diffusion. Using digital image processing, we measure the change in the reflectance of the filter paper.

We tested our sampler in a laboratory (exposing the sampler to kerosene soot in a controlled environment) and in 20 indoor locations in peri-urban Hyderabad, India. Field locations were inside households that cook using solid-fuels. Results indicate a high-degree of reproducibility and limits of detection appropriate for longer-term (~1 – 3 months) monitoring in the indoor locations studied. The tests document the precision of the method, but further testing is needed to quantify the method’s accuracy, including via comparison to “gold standard” techniques. The samplers described here are designed for mass-deployment to investigate long-term average levels of light-absorbing aerosols.