A high-resolution three-dimensional Eulerian transport and transformation model has been developed to simulate concentrations of tropospheric sulfate for specific times and locations; it was applied over the North Atlantic and adjacent continental regions during October and November 1986. The model represents emissions of anthropogenic SO2 and sulfate and of biogenic sulfur species, horizontal and vertical transport, gas phase oxidation of SO2 and dimethylsulfide, aqueous phase oxidation of SO2, and wet and dry deposition of SO2, sulfate, and methanesulfonic acid (MSA). The meteorological driver is the 6-hour output from the forecast model of the European Centre for Medium-Range Weather Forecasts. Calculated sulfate concentrations and column burdens, examined in detail for specific dates, are related to existing weather patterns. These quantities exhibit rich temporal and spatial structure; the characteristic (1/e) autocorrelation time for the sulfate column burdens over the central North Atlantic averages 10 hours; 95% of the values are 25 hours or less. The characteristic distance of spatial autocorrelation over this region depends on direction; the minimum value of the average is 900 km and the minimum values for the 10th and 90th percentiles are 400 and 1700 km. Daily average model sulfate concentrations at the lowest vertical level accurately represent the spatial variability, episodicity, and absolute magnitudes of surface concentrations measured by monitoring stations in Europe, Canada, New York state, and Barbados; over 50% of model concentrations are within a factor of 3 of the observations. Over 50% of weekly model sulfate wet deposition amounts are within a factor of 3 of observations from U.S. monitoring stations. Over the 34-day period modeled, contributions from anthropogenic emissions to the sulfate over the mid North Atlantic Ocean ranged from 44 to 66%, contributions from biogenic emissions were between 6 and 12%. Calculated average yields for sulfate (47 to 72%) and MSA (13%), and turnover times for SO2 (2 to 3 days) and sulfate and MSA (4 to 8 days) are comparable to previous estimates; however, these quantities depend on meteorological conditions and on the geographical and vertical distributions of the material.

Sulfate over the North Atlantic and adjacent continental regions: Evaluation for October and November 1986 using a three-dimensonal model driven by observation-derived meteorology

This paper is an overview of an intensive period of data collection performed as part of the Western Atlantic Ocean Experiment (WATOX) during early 1986. The objective of WATOX-86 was to determine the flux and fate of a variety of atmospheric materials that are advected eastward from North America to the atmosphere of the western North Atlantic Ocean (WNAO). WATOX-86 used two National Oceanic and Atmospheric Administration aircraft, a twin engine King Air and a four engine WP-3D, to collect gases and aerosols off the east coast of North America from Florida to Newfoundland. The WP-3D was based at McGuire Air Force Base, New Jersey, during the first 10 days of January 1986. The King Air was based at Hanscom Field, Massachusetts, during periods in January and February 1986 and on Bermuda during May 1986. Measurements were made of a variety of gases including SO2, NOx, NOy, peroxyacetyl nitrate, CO, O3, C2−C6 hydrocarbons, N2O and dimethyl sulfide. In addition, aerosols were collected and analyzed for black carbon, SO4=, NO3−, NH4+ and trace metals. The individual papers of this special issue provide details on the results and analysis of the individual measurement programs. This paper provides a brief summary of each program. During WATOX-86, there were large regions of the WNAO atmosphere that had elevated concentrations of the measured gas and aerosol species. The elevated concentrations were the result of transport of the products of anthropogenic activities from North America to the WNAO atmosphere. The high degree of correlation among the concentrations of the different species indicated that these materials were transported in “clouds” of polluted air that covered thousands of square kilometers. The WATOX-86 data on sulfur and nitrogen oxides are analyzed in the context of atmospheric budgets for WNAO. Approximately 25 to 35% of the sulfur and 15 to 25% of the nitrogen oxides emitted to the eastern North American atmosphere are advected eastward to the WNAO atmosphere. Of this material, about half of the sulfur and most of the nitrogen oxides are deposited to the WNAO. For both sulfur and nitrogen oxides, wet and dry deposition are of approximately equal importance.

Watox-86 overview and western North Atlantic Ocean S and N atmospheric budgets

Production of condensation nuclei in clean air by nucleation of H2SO4

Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO2) and methane (CH4). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH4/ppm CO2, a standard error of 0.6, and a correlation coefficient (r2) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.

Carbon dioxide and methane in the Arctic atmosphere

As a part of the Global Change Expedition/Coordinated Air-Sea Experiment/Western Atlantic Ocean Experiment (GCE/CASE/WATOX), size distributions of marine aerosols were measured at two altitudes of about 2750 and 150 m above sea level (asl) over the size range 0.1 ∼ 32 μm. Lognormal fitting was applied to the corrected aerosol size spectra to determine the volume and surface area size distributions of the CASE-WATOX marine aerosols. Each aerosol size distribution was fitted with three lognormal distributions representing fine-, large-, and giant-particle modes. Water volume fraction and dry particle size of each aerosol size distribution were also calculated using empirical formulas for particle size as a function of relative humidity and particle type. Because of the increased influence from anthropogenic sources in the continental United States, higher aerosol volume concentrations were observed in the fine-particle mode near-shore off the east coast; 2.11 and 3.63 μm3 cm−3 for free troposphere (FT) and marine boundary layer (MBL), compared with the open-sea Bermuda area values; 0.13 and 0.74 μm3 cm−3 for FT and MBL. The large-particle mode exhibits the least variations in volume distributions between the east coast and open-sea Bermuda area, having a volume geometric median diameter (VGMD) between 1.4 and 1.6 μm and a geometric standard deviation between 1.57 and 1.68. For the giant-particle mode, larger VGMD and volume concentrations were observed for marine aerosols nearshore off the east coast than in the open-sea Bermuda area because of higher relative humidity and higher surface wind speed conditions. Wet VGMD and aerosol water volume concentrations at 15 m asl ship level were determined by extrapolating from those obtained by analysis of the CASE-WATOX aircraft aerosol data. Abundance of aerosol water in the MBL serves as an important pathway for heterogeneous conversion of SO2 in sea salt aerosol particles.

Volume and surface area size distribution, water mass and model fitting of GCE/CASE/WATOX marine aerosols

Aerosol and ozone distributions over the western North Atlantic during WATOX‐86

A National Oceanic and Atmospheric Administration WP-3D meteorological research aircraft was instrumented with a wide range of gas and aerosol sampling equipment to conduct a component of the Western Atlantic Ocean Experiment (WATOX-86) intensive study. The added instrumentation provided for measurements of condensation nuclei, aerosol scattering extinction, ozone, soot carbon, NOx, SO2, H2O2, NO2, peroxyacetyl nitrate, CO, HNO3, and aerosol particle size/number. Discrete air samples were collected in both glass and metal flasks for analyses of a wide range of gaseous species. Aerosol collections included bulk samples on high-volume filters, single-particle collections with impactors, continuous size segregated aerosol impactors (with up to nine size cuts), and a range of specialty filters designed to collect gases and gases adsorbed on aerosols. Operational aspects of the four WP-3D WATOX flights are described along with pertinent observer notes and comments.

The National Oceanic and Atmospheric Administration Wp‐3d Meteorolgical, Aerosol, and Gas Systems, and flight operations, on Watox‐86

https://repository.library.noaa.gov/view/noaa/17821/noaa_17821_DS1.pdf

The analysis of meteorological conditions and haze distribution for the second Arctic Gas and Aerosol Sampling Program (AGASP II), March-April 1986

On January 4, 6, 8, and 9, 1986, a series of NOAA WP-3D research flights were conducted over the Western Atlantic Ocean, 2-300 km off the coast of North America. Flights were made perpendicular to NW airflow to establish the flux of gas and aerosol emissions from the east coast of North America. The following details are presented for each flight: a horizontal projection of the flight track on a latitude-longitude grid; the relevant synoptic situation; air-parcel back-trajectories; a flight log; vertical cross sections of potential temperature, mixing ratio, and flight track; vertical cross sections of condensation nuclei (CN) and aerosol scattering extinction (b sub sp); and representative aerosol size distributions.

Meteorological and aerosol measurements from the NOAA WP-3D aircraft during WATOX-86, January 4-9, 1986. Technical memo

Aircraft measurements of large and giant aerosols (1-45 μm diameter) in the marine boundary layer over the western North Atlantic (32°-40°N) under offshore flow conditions during the Western Atlantic Ocean Experiment on January 4, 6, and 9, 1986 (WATOX-86), showed a domination by sea salt, with volume spectra peaks between 7 and 9 μm diameter. Aerosol mass increased rapidly when short-term averaged wind speeds, ū, exceeded 17 m s−1. Aerosol mass also showed a qualitative dependence on relative humidity that was not as strong as the dependence on wind speed. Both wind speed and humidity variations can be used to explain the spatial variations in volume spectra along the flight track. Most models of sea salt mass or volume in the literature consider near-surface aerosol sizes smaller than 2.0-μm diameter and are not applicable to our data. At altitudes of 200-600 m above the sea surface our WATOX data show a strong nonlinear dependence between coarse aerosol mass and volume, and short-term wind speed. The best fit is a ū3 dependence (dry mass = 8.7 + 0.0065 ū3, R2 = 0.95; volume = 8.24 + 0.0065 ū3 R2 = 0.92). This dependence may have been enhanced by the offshore flow conditions that prevailed, and the location of the aircraft within 300 km of the coast.

Howard A. Bridgman

Papers

Aerosol and ozone distributions over the western North Atlantic during WATOX‐86

The National Oceanic and Atmospheric Administration Wp‐3d Meteorolgical, Aerosol, and Gas Systems, and flight operations, on Watox‐86

The analysis of meteorological conditions and haze distribution for the second Arctic Gas and Aerosol Sampling Program (AGASP II), March-April 1986

Meteorological and aerosol measurements from the NOAA WP-3D aircraft during WATOX-86, January 4-9, 1986. Technical memo

Large and giant aerosols in the marine boundary layer during WATOX, January 4‐9, 1986