Quantifying ambient aerosol absorption and scatter from nano- and micro-particle number concentrations

This research seeks to demonstrate the practicality of arriving at reasonably accurate broadband atmospheric absorption and scattering coefficients through <i>in situ</i> measurement of particulate matter with diameters less than 10 µm (<i>P</i><i>M</i>₁₀) ambient aerosol number concentrations. Combined with standard meteorological pressure, temperature, and relative humidity measurements, separately measured <i>P</i><i>M</i>_2.5 (particulate matter smaller than 2.5 µm) and <i>P</i><i>M</i>₁₀ number counts drive a standard, worldwide regional climatological aerosol model, which specifies aerosol optical properties according to type and wavelengths spanning ultraviolet through longwave infrared. A verified and validated atmospheric radiative transfer code applies the quantified number concentrations to climatological size distributions to calculate bulk absorption and scatter coefficients. To evaluate this proposition, optical closure is used to arrive at an ambient bulk aerosol refractive index (RI) based on a combination of standard Mie calculations using <i>in situ</i> point measurements of ambient bulk aerosol scattering and absorption as well as the polydisperse aerosol size distribution. The resultant bulk aerosol RI is comparatively evaluated with that defined in the worldwide climatological aerosol model. The research considers multiple sites and associated seasonal cycles, including an indoor laboratory. <i>In situ</i>, time-synchronous measurements of aerosol loading, binned size distributions, and optical properties were gathered in multiple settings, including both indoor laboratory environments and controlled aerosol chambers, as well as at the local Air Force Institute of Technology National Oceanic and Atmospheric Administration (NOAA) Federated Air Network (NFAN) Wright-Patterson Air Force Base (WPB) site.