Intercomparison of aerosol volume size distributions derived from AERONET ground based remote sensing and LARGE in situ aircraft profiles during the 2011–2014 DRAGON and DISCOVER-AQ experiments

Abstract. Aerosol volume size distributions (VSD) retrievals from the Aerosol Robotic Network (AERONET) aerosol monitoring network were obtained during multiple DRAGON (Distributed Regional Aerosol Gridded Observational Network) conducted in Maryland, California, Texas and Colorado from 2011 to 2014 . These VSD products were used during field campaigns to make comparisons with near simultaneous in situ sampling from aircraft profiles carried out by the NASA Langley Aerosol Group Experiment (LARGE) team as part of four campaigns comprising the DISCOVER-AQ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality) experiments. For coincident (p 1 hour) measurements there were a total of 91 profile-averaged fine mode size distributions acquired with the LARGE Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) instrument matched to 153 AERONET size distributions retrieved from almucantars at 22 different ground sites. These volume size distributions were characterized by two fine mode parameters, radius of peak concentration ( r peak_conc ) and VSD fine mode width ( width fine_mode ). The AERONET retrievals of these VSD fine mode parameters, derived from ground-based almucantar sun photometer data, represent ambient humidity values while the LARGE aircraft spiral profile retrievals provide dried aerosol (RH  r peak_conc was 0.033 p 0.035  μ m (ambient AERONET values were 15.8 % larger than dried LARGE values) and the average difference in width_fine_mode was 0.042 p 0.039  μ m (AERONET values were 25.7 % larger). When the LARGE retrieved values were adjusted to account for ambient humidification, the agreement notably improved with AERONET-LARGE average differences for r peak_conc decreasing to 0.011 p 0.019  μ m (AERONET values 5.2 % larger) and width fine_mode average differences decreasing to 0.030 p 0.037  μ m (AERONET values 15.8 % larger).