Measurement report: Aerosol vertical profiles over the Western North Atlantic Ocean during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES)

. The NASA North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) ship and aircraft field campaign deployed to the western subarctic Atlantic between the years 2015 and 2018. One of the primary goals of NAAMES is to improve the 25 understanding of aerosol-cloud interactions (ACI) over the Atlantic Ocean under different seasonal regimes. ACI currently represent the largest source of uncertainty in global climate models. During three NAAMES field campaigns (NAAMES-1 in November 2015, NAAMES-2 in May 2016, and NAAMES-3 in September 2017) multiple 10-hour science flights were conducted using the NASA C-130 aircraft to measure marine boundary layer aerosol and cloud properties. The standard flight pattern includes vertical spirals where the C-130 transitioned from high altitude to low-latitude (and vice versa) collecting in- 30 situ measurements of aerosols, trace gases, clouds, and meteorological parameters as a function of altitude. We examine the data collected from 37 spirals during the three NAAMES field campaigns, and we present a comprehensive characterization of the vertical profiles of aerosol properties under different synoptic conditions and aerosol regimes. The vertical distribution of submicron aerosol particles exhibited strong seasonal variation depending on emission sources and aerosol processes in the atmospheric column. Pristine marine conditions and new particle formation were prevalent in the wintertime (NAAMES-1) 35 due to low biogenic emissions from the surface ocean and reduced continental influence. Higher concentrations of submicron aerosol particles were observed in the spring (NAAMES-2) due to strong phytoplankton activity and the arrival of long-range-transported continental plumes in the free troposphere with subsequent entrainment into the marine boundary layer. Biomass burning from boreal wildfires was the main source of aerosol particles in the region during the late summer (NAAMES-3) in both the marine boundary layer and free troposphere. 40 by (Behrenfeld et al., 2019). During the campaigns, simultaneous ship- and aircraft-based observations of aerosols, trace gases, and clouds were collected in order to improve understanding of the aerosol and CCN budget sand their controlling processes over the WNAO. This study leverages aircraft and ship-based in-situ measurements of aerosol, trace gases, and meteorological parameters collected during the NAAMES field campaigns. We examine and discuss the vertical profiles of aerosol properties under different aerosol and meteorological regimes in relation to diverse emission sources, sink mechanisms, and thermodynamic structure of the atmospheric column. With this work, we aim to achieve a quantitative understanding of aerosol seasonal 30 variations over the WNAO and provide a framework for improving process-level understanding of marine aerosol-cloud interactions (ACI), which are critical to adequately link observations and climate modelling. This paper should be of interest to those seeking to understand the vertically-resolved, seasonal climatology of the remote marine atmosphere. In addition, we provide key observational constraints for evaluating aerosol-cloud interactions in models. legs subsequent to the spirals. Aerosol composition was investigated using an Aerodyne Research High-Resolution Aerosol Mass Spectrometer (HR-ToF-AMS; DeCarlo et al., 2006) on both the aircraft and ship. The AMS provides single particle composition measurements of the mass concentrations of non-refractory organic, sulfate, nitrate, and ammonium 40 at 30 second intervals on the ship and 1 Hz on the aircraft. We assess the contribution of anthropogenic sources using a Single Particle Soot Photometer at 0.1 Hz (SP2, DMT, Boulder, and particle loss by in-cloud precipitation 35 and coalescence scavenging during NAAMES-1 (Quinn et al., 2019). Similar results were also observed by Pennypacker and Wood (2017) in an earlier study conducted in the Eastern North Atlantic region. The aerosol number concentration in both MBL and FT is dominated by particles with D p < 100 nm. Geometric mean N NP are 32 ⋇ 3.1 cm -3 and 24 ⋇ 2.2 cm -3 in the MBL and the FT, respectively, and the average fraction of the NP mode particles is higher than in the other seasons in both MBL and FT, both being roughly a third of N CN (Fig. 7b). However, it is worth to note that the absolute number concentration of 40 accumulation modes. The passage of cold fronts associated with higher biogenic precursors in the spring over the WNAO might be the cause of the elevated N CN observed. Geometric mean concentrations of particles in the Aitken mode are 218 ⋇ 1.8 cm -3 in the MBL and 394 ⋇ 1.9 cm -3 in the FT, accounting for just 35 over half of N CN (Fig. 7c), while the geometric means of accumulation mode particle concentration is 40 ⋇ 2.3 cm -3 in the MBL (11% of N CN ) and 44 ⋇ 3.5 cm -3 in the FT (7% of N CN ) (Fig. 7c). Stronger ocean emissions and high DMS levels in the spring favour the growth of nucleation particles into Aitken and accumulation mode through condensation and coagulation (O’Dowd et al., 1997; Andreae et al., 2003). Here, we find substantially higher concentrations of accumulation particle modes (133 ⋇ 2.5 cm -3 ) when BC levels are higher than the threshold values of 40 ng m -3 (Pohl et al., 2014; Cavalli et al., 2016) indicate a 40 further contribution to to N At and N Ac from long-range transport of particles from polluted continental areas (Zhao et al., 2012; Wood et al., 2015). non-refractory particles suggest there is influence of long-range transported anthropogenic particles in the FT and biogenic oceanic emissions strongly contribute to the MBL on N CN and CCN budgets. In the summer, we found biomass burning from boreal wildfires to largely contribute to 40 aerosol concentrations and impact aerosol population. Particularly, enhanced concentration of large particles ( D p > 100 nm)