Portable optical particle spectrometers for the Office of Atmospheric Research, Chemical Sciences Laboratory

se in a field research project. The required OPCs are specifically the POPS. These instruments are needed for a project conducting globally distributed balloon sonde measurements of aerosol vertical profiles to study variability in stratospheric aerosol loading and properties. The science needs and sonde payload limitations impose instrument requirements of: Weight < 1 kg Power consumption < 6 W 100% minimum detectable particle size ? 140 nm diameter Capability to operate in high-altitude, low-pressure, and cold-temperature environments Ability to deliver 10 units by Sep 26, 2025, with partial deliveries permitted by production. Market Research Handix Scientific, Inc. has been identified as the only known source that can provide the POPS needed for use in the OAR CSL project that meet the Government�s intended use. A Source Sought notice was posted on August 1, 2025 and closed on August 8, 2025. No responses were received. Rationale for Sole Source Handix Scientific is the sole commercial producer of the POPS instrument that meets all the specified requirements for this project. The POPS instruments are compatible in form, fit, and function with existing systems and equipment used by CSL. CSL originally designed and constructed this sensor due to the lack of any available commercial instrument that met their needs, and Handix Scientific has replicated this design. No other commercially available optical particle counter (OPC) instruments meet the stringent requirements for this project, particularly regarding size, weight, power consumption, and low particle size detection limit for high-altitude, low-pressure, and cold-temperature environments. Alternative instruments either do not achieve the necessary detection limits, have not been demonstrated to work at high altitudes, or have significantly higher power consumption, making them unsuitable for battery-operated balloon sonde flights. Without the requested procurement of POPS instruments from Handix Scientific, CSL would not be able to successfully carry out this critical research project, jeopardizing the scientific objectives of studying stratospheric aerosol loading and properties.