Evaluation of the Density and Absorption Properties of Laboratory-Generated Particulate Organic Nitrates (pON)

Atmospheric particulate organic nitrates (pON) have recently been shown to account for a large fraction of organic aerosol (OA). Through light absorption, especially at short wavelengths, they make up part of atmospheric brown carbon. While pON might be a non-negligible climate-forcing agent, the physical and optical properties are still poorly documented. As part of the Aerosol Chemical Monitor Calibration Centre (ACMCC) pON experiment, measurements have been conducted to characterize the physical and optical properties of laboratory-generated pON, such as density, mass absorption coefficient (MAC) and refractive index (RI). pON were generated in a Potential Aerosol Mass oxidation flow reactor from the reaction of single VOC precursors with NO3 radical, using two biogenic (limonene and b-pinene) and two anthropogenic (acenaphthylene and guaiacol) compounds. In addition to online physicochemical characterization with aerosol mass spectrometers, a suite of instruments was dedicated to study the physical and optical pON properties, including an aerodynamic aerosol classifier (AAC), a centrifugal particle mass analyzer (CPMA), a scanning mobility particle sizer (SMPS), a condensation particle counter (CPC) and a multi-wavelength aethalometer (AE33). Results will be discussed according to different precursors (biogenic/anthropogenic), as well as compared to the literature data from laboratory experiments for the same (and other) precursors but in different chemical conditions, such as OH or NH3 exposure. Results for laboratory-generated pON will also be compared with ambient air observations.