Mobile Urban Aerosol Composition using a Robust Multi-pass Cell and Mid-infrared Fingerprint Region Spectroscopy

Atmospheric particulate matter (PM) in urban environments is a key concern for two reasons. First, high PM load is associated with a wide range of negative health impacts including cancer, respiratory issues, and cardiovascular disease. Second, PM impacts climate and surrounding ecosystems by changing albedo and seeding local and downwind precipitation patterns. Despite the importance of measuring the chemical composition of aerosols with high spatial and temporal resolution in urban environments, there remain many challenges due to deficiencies of existing methods such as slow response speed, high cost and large size. In this Small Business Innovative Research (SBIR) program, Nikira Labs Inc. proposes to design, build, and deploy multiple lightweight, real-time analyzers capable of characterizing and quantifying aerosol functional groups in situ, from mobile platforms in urban environments. The analyzers will determine aerosol composition by measuring aerosol optical absorption in the mid-infrared (MIR) fingerprint region (7.6 ľ 10.4 µm) using external cavity quantum cascade lasers (EC-QCL) paired with Nikira Labsĺ patent pending non-paraxial, multipass (NP-MP) cell. This innovative cell design creates effective optical path lengths >300 m, has high optical transmission efficiency and is robust to small changes in mirror reflectivity. This set of properties allows for the direct measurement of aerosol absorption in the MIR at urban aerosol loadings (single µg/m3 range) with an open cell configuration and from a mobile platform. In Phase I, Nikira Labs will develop the mechanical structure for the NP-MP cell, fabricate the analyzer components, and build a prototype system. The instrument will be extensively laboratory tested to determine its accuracy, precision, linearity, dynamic range, and immunity to vibration and thermal changes. Additionally, Nikira will evaluate several methods of analyzing the data to extract functional group distributions (e.g., CľC, CľN, CľO, CľCl, etc.). Subsequent to this development and testing, Nikira Labs will deploy the sensor for both terrestrial and mobile sensing in local urban environments. Finally, the Phase I results will be used to design a series of Phase II instruments that extends the probed wavelength range by leveraging MIR light emitting diodes (LEDs), additional QCLs, and/or supercontinuum sources. In Phase II, Nikira Labs will fabricate multiple units (2 ľ 3) with the enhanced wavelength region and other Phase I improvements. These systems will be extensively tested before being deployed by Nikira for mobile urban measurements with a commercial partner and at stationary aerosol measurement facilities for comparison with existing instrumentation. The resulting portable, real-time, aerosol functional group analyzer will be commercialized to allow governmental and academic researchers and commercial mobile surveyors to characterize aerosol chemistry in urban environments to aid in mitigation of unhealthy aerosol emissions.