Challenges in remote sensing of CCN concentration: a comprehensive assessment with airborne measurements of AOD, CCN, chemical composition, size distribution, light scattering/absorption and humidity response in North America

The aerosol distribution and the subset known as cloud condensation nuclei (CCN) are too heterogeneous in space and time to comprehensively measure from ground, ship or aircraft. Global assessment of aerosol effects would be facilitated by the extended and frequent coverage of satellite observations. Satellites, however, do not directly measure the CCN concentration. Satellite-derived aerosol size distributions are estimated based on radiances received from particles larger than most CCN, using predetermined aerosol models. The objectives of the present work are to optimize a remote sensing scheme for CCN concentration over North America and to determine expected errors for aerosol types, regions and meteorological settings. To this end, we examine the relationships of the aerosol optical depth (AOD), a common satellite product, to the near-surface ambient extinction coefficient, dry extinction coefficient and CCN concentration, step by step in this order. For these analyses we use remote sensing and in-situ measurements of aerosol properties (AOD, CCN, chemical composition, size distribution, light scattering/absorption and humidity response) made from NASA P-3 aircraft during the ARCTAS campaign at high latitudes over North America.