T. S. Bates

Sea spray aerosol (SSA) consists of both sea salt and organic components. These aerosols affect Earth's climate by scattering solar radiation and by altering cloud properties. Here we present observations of SSA particles generated at sea using an over‐the‐side bubbling system (Sea Sweep) and an onboard plunging wave mesocosm (Marine Aerosol Reference Tank—MART) during five cruises in the North Atlantic. The cruises were timed to sample different stages of the North Atlantic plankton bloom and included transects from the oligotrophic Sargasso Sea to the biologically productive western subarctic. The results show that the North Atlantic plankton bloom has little effect on the emission flux, organic fraction, or cloud condensation nuclei (CCN) activity of SSA, and therefore, plankton ecosystems do not need to be included in modeling aerosol indirect effects of primary SSA in global climate models or in chemical transport models.

Atmospheric aerosol vertical distributions were measured above Svalbard, Norway, in April 2011 during the Cooperative Investigation of Climate-Cryosphere Interactions campaign (CICCI). Measurements were made of the particle number concentration and the aerosol light absorption coefficient at three wavelengths. A filter sample was collected on each flight at the altitude of maximum particle number concentration. The filters were analyzed for major anions and cations. The aerosol payload was flown in a NOAA/PMEL MANTA Unmanned Aerial System (UAS). A total of 18 flights were flown during the campaign totaling 38 flight hours. The data show frequent aerosol layers aloft with high particle number concentration (1000 cm⁻³) and enhanced aerosol light absorption (1 Mm⁻¹). Air mass histories of these aerosol layers were assessed using FLEXPART particle dispersion modeling. The data contribute to an assessment of sources of BC to the Arctic and potential climate impacts.

Reliable characterization of particles freshly emitted from the ocean surface requires a sampling method that is able to isolate those particles and prevent them from interacting with ambient gases and particles. Here we report measurements of particles directly emitted from the ocean using a newly developed in situ particle generator (Sea Sweep). The Sea Sweep was deployed alongside R/V Atlantis off the coast of California during May of 2010. Bubbles were generated 0.75 m below the ocean surface with stainless steel frits and swept into a hood/vacuum hose to feed a suite of aerosol instrumentation on board the ship. The number size distribution of the directly emitted, nascent particles had a dominant mode at 55–60 nm (dry diameter) and secondary modes at 30–40 nm and 200–300 nm. The nascent aerosol was not volatile at 230°C and was not enriched in SO₄⁼, Ca⁺⁺, K⁺, or Mg⁺⁺above that found in surface seawater. The organic component of the nascent aerosol (7% of the dry submicrometer mass) volatilized at a temperature between 230 and 600°C. The submicrometer organic aerosol characterized by mass spectrometry was dominated by non‐oxygenated hydrocarbons. The nascent aerosol at 50, 100, and 145 nm dry diameter behaved hygroscopically like an internal mixture of sea salt with a small organic component. The CCN/CN activation ratio for 60 nm Sea Sweep particles was near 1 for all supersaturations of 0.3 and higher indicating that all of the particles took up water and grew to cloud drop size. The nascent organic aerosol mass fraction did not increase in regions of higher surface seawater chlorophyll but did show a positive correlation with seawater dimethylsulfide (DMS).

The air quality and climate forcing impacts of atmospheric aerosols in a metropolitan region depend on the amount, composition, and size of the aerosol transported into the region; the input and removal of aerosols and aerosol precursors within the region; and the subsequent chemical processing in the atmosphere. These factors were studied in the Houston‐Galveston‐Gulf of Mexico region, aboard the NOAA R/V Ronald H. Brown during the Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS 2006). The aerosol measured in the Gulf of Mexico during onshore flow (low radon concentrations indicating no contact with land for several days) was highly impacted by Saharan dust and what appear to be ship emissions (acidic sulfate and nitrate). Mean (median) mass concentrations of the total submicrometer and supermicrometer aerosol were 6.5 (4.6) μg m⁻³ and 17.2 (8.7) μg m⁻³, respectively. These mass loadings of “background” aerosol are much higher than typically observed in the marine atmosphere and thus have a substantial impact on the radiative energy balance over the Gulf of Mexico and particulate matter (PM) loadings (air quality) in the Houston‐Galveston area. As this background aerosol moved onshore, local urban and industrial sources added an organic rich submicrometer component (66% particulate organic matter (POM), 20% sulfate, 14% elemental carbon) but no significant supermicrometer aerosol. The resulting aerosol had mean (median) mass concentrations of the total submicrometer and supermicrometer aerosol of 10.0 (9.1) μg m⁻³ and 16.8 (11.2) μg m⁻³, respectively. These air masses, with minimal processing of urban emissions contained the highest SO₂/(SO₂ + SO₄⁼) ratios and the highest hydrocarbon‐like organic aerosol to total organic aerosol ratios (HOA/POM). In contrast, during periods of offshore flow, the aerosol was more processed and, therefore, much richer in oxygenated organic aerosol (OOA). Mean (median) mass concentrations of the total submicrometer and supermicrometer aerosol were 20.8 (18.6) μg m⁻³ and 7.4 (5.0) μg m⁻³, respectively. Sorting air masses based on their trajectories and time over land provides a means to examine the effects of transport and subsequent chemical processing. Understanding and parameterizing these processes is critical for the chemical transport modeling that forms the basis for air quality forecasts and radiative forcing calculations.

The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions (IPCC, 2001). Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean (NIO) during INDOEX, the Northwest Pacific Ocean (NWP) during ACE-Asia, and the Northwest Atlantic Ocean (NWA) during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth (AOD), and direct radiative effect of aerosols (DRE – change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Constraining the radiative transfer calculations by observational inputs increases the clear-sky, 24-h averaged AOD (34±8%), top of atmosphere (TOA) DRE (32±12%), and TOA direct climate forcing of aerosols (DCF – change in radiative flux due to anthropogenic aerosols) (37±7%) relative to values obtained with "a priori" parameterizations of aerosol loadings and properties (GFDL RTM). The resulting constrained clear-sky TOA DCF is −3.3±0.47, −14±2.6, −6.4±2.1 Wm⁻² for the NIO, NWP, and NWA, respectively. With the use of constrained quantities (extensive and intensive parameters) the calculated uncertainty in DCF was 25% less than the "structural uncertainties" used in the IPCC-2001 global estimates of direct aerosol climate forcing. Such comparisons with observations and resultant reductions in uncertainties are essential for improving and developing confidence in climate model calculations incorporating aerosol forcing.

The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions (IPCC, 2001). Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean (NIO) during INDOEX, the Northwest Pacific Ocean (NWP) during ACE-Asia, and the Northwest Atlantic Ocean (NWA) during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth (AOD), and direct radiative effect of aerosols (DRE – change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Constraining the radiative transfer calculations by observational inputs increases the clear-sky, 24-h averaged AOD (34±8%), top of atmosphere (TOA) DRE (32±12%), and TOA direct climate forcing of aerosols (DCF – change in radiative flux due to anthropogenic aerosols) (37±7%) relative to values obtained with "a priori" parameterizations of aerosol loadings and properties (GFDL RTM). The resulting constrained clear-sky TOA DCF is −3.3±0.47, −14±2.6, −6.4±2.1 Wm⁻² for the NIO, NWP, and NWA, respectively. With the use of constrained quantities (extensive and intensive parameters) the calculated uncertainty in DCF was 25% less than the "structural uncertainties" used in the IPCC-2001 global estimates of direct aerosol climate forcing. Such comparisons with observations and resultant reductions in uncertainties are essential for improving and developing confidence in climate model calculations incorporating aerosol forcing.

Aerosol chemical, physical, and optical measurements were made aboard the NOAA R/V Ronald H. Brown off the coast of New England from July 12 through August 10, 2002, as part of the New England Air Quality Study (NEAQS). Measurements (generally 20 to 100 km from the coast) were made downwind of urban centers (New York City, Boston) and rural areas, and in air masses that had not been in contact with land for several days. On average during NEAQS, 75 ± 8% of the sub‐10 μm aerodynamic diameter dry aerosol mass sampled 18 m above the sea surface was in the sub‐1 μm fraction (size cut at 55% RH). The major submicrometer aerosol components were ammonium sulfate and particulate organic matter (POM, defined here as 1.6 times the mass concentration of organic carbon) comprising more than 92 ± 4% of the total mass. Under northwesterly flow with an average submicrometer total mass concentrations of 11 ± 4.5 μg m⁻³, POM was the dominant component (68 ± 8%) followed by (NH₄)_xH_ySO₄ (23 ± 8%), inorganic oxidized material (IOM) (6 ± 4%), and EC (3 ± 1%). Under southwesterly flow with an average submicrometer total mass concentrations of 30 ± 11 μg m⁻³, (NH₄)_xH_ySO₄ was the dominant component (54 ± 9%) followed by POM (41 ± 9%), IOM (3 ± 2%), and EC (2 ± 1%). Mie calculations using submicrometer nonrefractory (NR) POM and NR (NH₄)_xH_ySO₄ + H₂O size distributions to calculate submicrometer light scattering (σ_sp) at a wavelength of 550 nm suggest that POM was a dominant chemical component contributing to aerosol light scattering (haze) during NEAQS 2002, and contributed 60 ± 6 % and 57 ± 11 % to σ_sp at 55% RH during two pollution episodes off the New England Coast. These results are similar to those from the mid‐Atlantic states during TARFOX but contrary to the long‐term monitoring measurements over the continental northeast United States that show the New England haze is primarily a result of sulfate aerosol.

Analysis of the aerosol properties during 3 recent international field campaigns (ACE-1, TARFOX and ACE-2) are described using satellite retrievals from NOAA AVHRR data. Validation of the satellite retrieval procedure is performed with airborne, shipboard, and land-based sunphotometry during ACE-2. The intercomparison between satellite and surface optical depths has a correlation coefficient of 0.93 for 630 nm wavelength and 0.92 for 860 nm wavelength. The standard error of estimate is 0.025 for 630 nm wavelength and 0.023 for 860 nm wavelength. Regional aerosol properties are examined in composite analysis of aerosol optical properties from the ACE-1, TARFOX and ACE-2 regions. ACE-1 and ACE-2 regions have strong modes in the distribution of optical depth around 0.1, but the ACE-2 tails toward higher values yielding an average of 0.16 consistent with pollution and dust aerosol intrusions. The TARFOX region has a noticeable mode of 0.2, but has significant spread of aerosol optical depth values consistent with the varied continental aerosol constituents off the eastern North American Coast. DOI: 10.1034/j.1600-0889.2000.00040.x

Analysis of the aerosol properties during 3 recent international field campaigns (ACE-1, TARFOX and ACE-2) are described using satellite retrievals from NOAA AVHRR data. Validation of the satellite retrieval procedure is performed with airborne, shipboard, and land-based sunphotometry during ACE-2. The intercomparison between satellite and surface optical depths has a correlation coefficient of 0.93 for 630 nm wavelength and 0.92 for 860 nm wavelength. The standard error of estimate is 0.025 for 630 nm wavelength and 0.023 for 860 nm wavelength. Regional aerosol properties are examined in composite analysis of aerosol optical properties from the ACE-1, TARFOX and ACE-2 regions. ACE-1 and ACE-2 regions have strong modes in the distribution of optical depth around 0.1, but the ACE-2 tails toward higher values yielding an average of 0.16 consistent with pollution and dust aerosol intrusions. The TARFOX region has a noticeable mode of 0.2, but has significant spread of aerosol optical depth values consistent with the varied continental aerosol constituents off the eastern North American Coast.