A comparison of aerosol chemical and optical properties from the 1st and 2nd Aerosol Characterization Experiments

Shipboard measurements of aerosol chemical composition and optical properties were made during both ACE-1 and ACE-2. ACE-1 focused on remote marine aerosol minimally perturbed by continental sources. ACE-2 studied the outflow of European aerosol into the NE Atlantic atmosphere. A variety of air masses were sampled during ACE-2 including Atlantic, polar, Iberian Peninsula, Mediterranean, and Western European. Reported here are mass size distributions of non-sea salt (nss) sulfate, sea salt, and methanesulfonate and submicron and supermicron concentrations of black and organic carbon. Optical parameters include submicron and supermicron aerosol scattering and backscattering coefficients at 550 nm, the absorption coefficient at 550±20 nm, the Ångström exponent for the 550 and 700 nm wavelength pair, and single scattering albedo at 550 nm. All data are reported at the measurement relative humidity of 55%. Measured concentrations of nss sulfate aerosol indicate that, relative to ACE-1, ACE-2 aerosol during both marine and continental flow was impacted by continental sources. Thus, while sea salt controlled the aerosol chemical composition and optical properties of both the submicron and supermicron aerosol during ACE-1, it played a relatively smaller role in ACE-2. This is confirmed by the larger average Ångström exponent for ACE-2 continental aerosol of 1.2±0.26 compared to the ACE-1 average of -0.03±0.38. The depletion of chloride from sea salt aerosol in ACE-2 continental air masses averaged 55±25% over all particle sizes. This compares to the ACE-2 marine average of 4.8±18% and indicates the enhanced interaction of anthropogenic acids with sea salt as continental air masses are transported into the marine atmosphere. Single scattering albedos averaged 0.95±0.03 for ACE-2 continental air masses. Averages for ACE-2 and ACE-1 marine air masses were 0.98±0.01 and 0.99±0.01, respectively

Aerosol physical properties and processes in the lower marine boundary layer: A comparison of shipboard sub-micron data from ACE-1 and ACE-2

The goals of the IGAC Aerosol Characterization Experiments (ACE) are to determine and understand the properties and controlling processes of the aerosol in a globally representative range of natural and anthropogenically perturbed environments. ACE-1 was conducted in the remote marine atmosphere south of Australia while ACE-2 was conducted in the anthropogenically modified atmosphere of the Eastern North Atlantic. In-situ shipboard measurements from the RV Discoverer(ACE-1) and the RV Professor Vodyanitskiy(ACE-2), combined with calculated back trajectories can be used to define the physical properties of the sub-micron aerosol in marine boundary layer (MBL) air masses from the remote Southern Ocean, Western Europe, the Iberian coast, the Mediterranean and the background Atlantic Ocean. The differences in these aerosol properties, combined with dimethylsulfide, sulfur dioxide and meteorological measurements provide a means to assess processes that affect the aerosol distribution. The background sub-micron aerosol measured over the Atlantic Ocean during ACE-2 was more abundant (number and volume) and appeared to be more aged than that measured over the Southern Ocean during ACE-1. Based on seawater DMS measurements and wind speed, the oceanic source of non-sea-salt sulfur and sea-salt to the background marine atmosphere during ACE-1 and ACE-2 was similar. However, the synoptic meteorological pattern was quite different during ACE-1 and ACE-2. The frequent frontal passages during ACE-1 resulted in the mixing of nucleation mode particles into the marine boundary layer from the free troposphere and relatively short aerosol residence times. In the more stable meteorological setting of ACE-2, a significant nucleation mode aerosol was observed in the MBL only for a half day period associated with a weak frontal system. As a result of the longer MBL aerosol residence times, the average background ACE-2 accumulation mode aerosol had a larger diameter and higher number concentration than during ACE-1. The sub-micron aerosol number size distributions in the air masses that passed over Western Europe, the Mediterranean, and coastal Portugal were distinctly different from each other and the background aerosol. The differences can be attributed to the age of the air mass and the degree of cloud processing

Isotopic measurements in water vapor, precipitation, and seawater during EUREC4^4A

n early 2020, an international team set out to investigate trade-wind cumulus clouds and their coupling to the large-scale circulation through the field campaign EUREC$^4$A: ElUcidating the RolE of Clouds-Circulation Coupling in ClimAte. Focused on the western tropical Atlantic near Barbados, EUREC$^4$A deployed a number of innovative observational strategies, including a large network of water isotopic measurements collectively known as EUREC$^4$A-iso, to study the tropical shallow convective environment. The goal of the isotopic measurements was to elucidate processes that regulate the hydroclimate state – for example, by identifying moisture sources, quantifying mixing between atmospheric layers, characterizing the microphysics that influence the formation and persistence of clouds and precipitation, and providing an extra constraint in the evaluation of numerical simulations. During the field experiment, researchers deployed seven water vapor isotopic analyzers on two aircraft, on three ships, and at the Barbados Cloud Observatory (BCO). Precipitation was collected for isotopic analysis at the BCO and from aboard four ships. In addition, three ships collected seawater for isotopic analysis. All told, the in situ data span the period 5 January–22 February 2020 and cover the approximate area 6 to 16° N and 50 to 60° W, with water vapor isotope ratios measured from a few meters above sea level to the mid-free troposphere and seawater samples spanning the ocean surface to several kilometers depth. This paper describes the full EUREC$^4$A isotopic in situ data collection – providing extensive information about sampling strategies and data uncertainties – and also guides readers to complementary remotely sensed water vapor isotope ratios. All field data have been made publicly available even if they are affected by known biases, as is the case for high-altitude aircraft measurements, one of the two BCO ground-based water vapor time series, and select rain and seawater samples from the ships. Publication of these data reflects a desire to promote dialogue around improving water isotope measurement strategies for the future. The remaining, high-quality data create unprecedented opportunities to close water isotopic budgets and evaluate water fluxes and their influence on cloudiness in the trade-wind environment. The full list of dataset DOIs and notes on data quality flags are provided in Table 3 of Sect. 5 (“Data availability”)

Particulate emissions from commercial shipping: chemical, physical, and optical properties

, 39% OM, and 15% BC and differs from inventories that used 81%, 14%, and 5% and 31%, 63%, and 6% SO 4 2À , OM, and BC, respectively. SO 4 2À and OM mass were found to be dependent on fuel sulfur content as were SSA, hygroscopicity, and CCN concentrations. BC mass was dependent on engine type and combustion efficiency. A plume evolution study conducted on one vessel showed conservation of particle light absorption, decrease in CN > 5 nm, increase in particle hygroscopicity, and an increase in average particle size with distance from emission. These results suggest emission of small nucleation mode particles that subsequently coagulate/condense onto larger BC and OM. This work contributes to an improved understanding of the impacts of ship emissions on climate and air quality and will also assist in determining potential effects of altering fuel standards

Processes controlling the distribution of aerosol particles in the lower marine boundary layer during the First Aerosol Characterization Experiment (ACE 1)

The goals of the International Global Atmospheric Chemistry (IGAC) Program's First Aerosol Characterization Experiment (ACE 1) are to determine and understand the properties and controlling factors of the aerosol in the remote marine atmosphere that are relevant to radiative forcing and climate. A key question in terms of this goal and the overall biogeochemical sulfur cycle is what factors control the formation, growth, and evolution of particles in the marine boundary layer (MBL). To address this question, simultaneous measurements of dimethylsulfide (DMS), sulfur dioxide (SO2), the aerosol chemical mass size distribution, and the aerosol number size distribution from 5 to 10,000 nm diameter were made on the National Oceanic and Atmospheric Administration (NOAA) ship Discoverer. From these data we conclude that the background MBL aerosol during ACE 1 often was composed of four distinct modes: an ultrafine (UF) mode (Dp  = 5–20 nm), an Aitken mode (Dp  = 20–80 nm), an accumulation mode (Dp  = 80–300 nm), and a coarse mode (Dp  > 300 nm). The presence of UF mode particles in the MBL could be explained by convective mixing between the free troposphere (FT) and the MBL associated with cloud pumping and subsidence following cold frontal passages. There was no evidence of major new particle production in the MBL. Oceanic emissions of DMS appeared to contribute to the growth of Aitken and accumulation mode particles. Coarse mode particles were comprised primarily of sea salt. Although these particles result from turbulence at the air-sea interface, the instantaneous wind speed accounted for only one third of the variance in the coarse mode number concentration in this region

Marine boundary layer dust and pollutant transport associated with the passage of a frontal system over eastern Asia

Aerosol chemical composition and number size distributions were measured aboard the R/V Ronald H. Brown during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) from 14 March to 20 April 2001. This manuscript focuses on the prefrontal and postfrontal air masses sampled aboard the ship in the Sea of Japan between 6 and 15 April 2001 to illustrate the different chemical sources/mixtures off the coast of Asia resulting from the contrasting meteorological transport patterns. The prefrontal air masses had a dominant accumulation mode composed of pollution and volcanic aerosols. The aerosol was predominately ammonium sulfate and organic carbon. Minor amounts of dust were present in the marine boundary layer (MBL) as a result of subsidence from a pronounced Taklimakan dust aerosol layer aloft. The sea salt in both the submicron and supermicron modes was highly depleted in chloride from reaction with sulfuric and nitric acid vapors. The passage of a large low-pressure center, surrounded by a widespread distribution of airborne dust, on 10 April brought elevated concentrations of submicron and supermicron Gobi desert dust to the ship. The supermicron dust particles contained high concentrations of sulfate, nitrate, organic, and elemental carbon. The MBL aerosol properties and controlling processes described here provide data to evaluate and refine chemical transport models. Copyright 2004 by the American Geophysical Union

Processes controlling the distribution of aerosol particles in the lower marine boundary layer during the First Aerosol Characterization Experiment (ACE 1)

The goals of the International Global Atmospheric Chemistry (IGAC) Program's First Aerosol Characterization Experiment (ACE 1) are to determine and understand the properties and controlling factors of the aerosol in the remote marine atmosphere that are relevant to radiative forcing and climate. A key question in terms of this goal and the overall biogeochemical sulfur cycle is what factors control the formation, growth, and evolution of particles in the marine boundary layer (MBL). To address this question, simultaneous measurements of dimethylsulfide (DMS), sulfur dioxide (SO2), the aerosol chemical mass size distribution, and the aerosol number size distribution from 5 to 10,000 nm diameter were made on the National Oceanic and Atmospheric Administration (NOAA) ship Discoverer. From these data we conclude that the background MBL aerosol during ACE I often was composed of four distinct modes: an ultrafine (UF) mode (Dp = 5-20 nm), an Aitken mode (Dp = 20-80 nm), an accumulation mode (Dp = 80-300 nm), and a coarse mode (Dp > 300 nm). The presence of UF mode particles in the MBL could be explained by convective mixing between the free troposphere (FT) and the MBL associated with cloud pumping and subsidence following cold frontal passages. There was no evidence of major new particle production in the MBL. Oceanic emissions of DMS appeared to contribute to the growth of Aitken and accumulation mode particles. Coarse mode particles were comprised primarily of sea salt. Although these particles result from turbulence at the air-sea interface, the instantaneous wind speed accounted for only one third of the variance in the coarse mode number concentration in this region.This research was funded by the Aerosol Project of the NOAA Climate and Global Change Program