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

<p>Aerosol volume size distribution (VSD) retrievals from the Aerosol Robotic Network (AERONET) aerosol monitoring network were obtained during multiple DRAGON (Distributed Regional Aerosol Gridded Observational Network) campaigns conducted in Maryland, California, Texas and Colorado from 2011 to 2014. These VSD retrievals from the field campaigns were used to make comparisons with near-simultaneous in situ samples 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 (<span class="inline-formula">±1</span>&thinsp;h) 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, the radius of peak concentration (<span class="inline-formula"><i>r</i>_{peak_conc}</span>) and the VSD fine-mode width (width<span class="inline-formula">_{peak_conc}</span>). 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 (relative humidity; RH&thinsp;<span class="inline-formula">&lt;20</span>&thinsp;%) values. For the combined multiple campaign dataset, the average difference in <span class="inline-formula"><i>r</i>_{peak_conc}</span> was <span class="inline-formula">0.033±0.035</span>&thinsp;<span class="inline-formula">µm</span> (ambient AERONET values were 15.8&thinsp;% larger than dried LARGE values), and the average difference in width<span class="inline-formula">_{peak_conc}</span> was <span class="inline-formula">0.042±0.039</span>&thinsp;<span class="inline-formula">µm</span> (AERONET values were 25.7&thinsp;% larger). For a subset of aircraft data, the LARGE data were adjusted to account for ambient humidification. For these cases, the AERONET–LARGE average differences were smaller, with <span class="inline-formula"><i>r</i>_{peak_conc}</span> differing by <span class="inline-formula">0.011±0.019</span>&thinsp;<span class="inline-formula">µm</span> (AERONET values were 5.2&thinsp;% larger) and width<span class="inline-formula">_{peak_conc}</span> average differences equal to <span class="inline-formula">0.030±0.037</span>&thinsp;<span class="inline-formula">µm</span> (AERONET values were 15.8&thinsp;% larger).</p>