Martin K. Hill

Production of sea spray aerosol in the surf zone

quantitative source function for sea spray aerosol produced by waves breaking in the surf zone was determined from data collected with optical particle counters at both sides of the surf zone at two locations on the Californian coast. Three optical particle counters were used to measure profiles at the base of a pier; a fourth instrument was used at the end of the pier. Careful calibration and intercomparisons of the instruments were made to avoid systematic errors. Aerosol concentrations measured downwind from the surf, in wind speeds of up to 9 m s-1, were 1-2 orders of magnitude higher than those upwind. Surf aerosol concentration gradients and plume heights vary with particle size and with wind speed. The derived surf aerosol source functions are compared with current estimates for the open ocean, taking into account the different proportions of the ocean surface covered by whitecaps. Application of a simple transport model indicates that surf-produced sea spray contributes significantly to the aerosol concentrations at fetches up to at least 25 km. This has implications for, for example, heterogeneous chemistry and electro-optical propagation. Copyright 2000 by the American Geophysical Union.

An analysis of rapid increases in condensation nuclei concentrations at a remote coastal site in western Ireland.

Massive “bursts” in condensation nuclei (CN) concentration were recorded at a remote site on the west Irish coast during campaigns in summer 1996 and spring/summer 1997. Number concentrations of 3–7 nm diameter CN were observed to rise daily from 102–103 up to ∼105 /cm3 for 1–3 hours. Data were collected as part of the Atmospheric Chemistry Studies in the Oceanic Environment program. In a previous paper the burst phenomenon was linked to the movement of the tide, and it was suggested that enhanced biogenic emissions occurred near low tide with concomitant rapid homogeneous gas phase CN formation. In this paper possible chemical mechanisms for the burst phenomenon are investigated. Two approaches are adopted. First, by assuming a 20:80 sulfate:water molar composition and calculating the number distribution using data from condensation particle counters, the total mass of CN formed during a burst is evaluated. This is compared with that mass of sulfate produced by OH-initiated dimethyl sulfide (DMS) oxidation. The procedure is termed “mass balance.” Second, a variety of chemical species are coplotted with tidal height. DMS oxidation is not believed to play a major role in CN formation at this site because (1) the mass balance calculations imply ambient DMS concentrations higher than those observed, and (2) gas phase HCl, HNO3, SO2, and NH3 did not exhibit any discernible correlation with tidal height. Further, none of the suite of observed nonmethane hydrocarbons or DMS showed a tidal relation. No mechanism has to date been convincingly identified for the burst phenomenon.

PHYSICAL EXCHANGES AT THE AIR-SEA INTERFACE UK-SOLAS Field Measurements

As part of the U.K. contribution to the international Surface Ocean–Lower Atmosphere Study, a series of three related projects—DOGEE, SEASAW, and HiWASE—undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosol-size spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.

Size-differentiated volatility analysis of internally mixed laboratory-generated aerosol

Abstract The increased application of volatility analysis to determine the composition and structure of sub-micron aerosol requires that the thermal behaviour of chemically complex aerosol be understood. Presented here is a volatility study, utilising a tandem volatility differential mobility analyser (TVDMA), of 30, 50, and 70 nm radii, internally mixed, aerosol containing ionic-salts, acids, organics, and carbon. Evidence of some size-dependent behaviour was observed with several of the single component aerosol. Internally mixed aerosol displayed complex thermal behaviours that were dependent on both size and the volume mixing ratio of source solutions.

A Compact Lightweight Aerosol Spectrometer Probe (CLASP)

The Compact Lightweight Aerosol Spectrometer Probe (CLASP) is an optical particle spectrometer capable of measuring size-resolved particle concentrations in 16 user-defined size bins spanning diameters in the range 0.24 D 18.5 m at a rate of 10 Hz. The combination of its compact nature and lightweight and robust build allows for deployment in environments and locations where the use of the larger, heavier, more traditional instrumentation would prove awkward or impossible. The high temporal resolution means it is particularly suited to direct measurements of aerosol fluxes via the eddy covariance technique. CLASP has been through an extended evolutionary development. This has resulted in an instrument whose performance characteristics are well established.

Aerosol production in the surf zone and effects on IR extinction

Aerosol concentrations over the surf were measured during the EOPACE (Electro-Optical Propagation Assessment in Coastal Environment) Surf-i experiment in La Jolla, California. Particle size distributions were measured on the beach (at three levels) and across the surf (one level). Concentrations of droplets smaller than i im in diameter are little affected by the surf, while those with diameters in the 1-10 im range increase by up to two orders of magnitude. Clear vertical gradients were observed, which vary with particle size. No relation could be established between the surf production and wind speed or wave properties. Extinction coefficients at visible and infrared wavelengths calculated from the particle size distributions show that these are enhanced by a factor of 30 to 100, depending on the wavelength. Using the measured concentrations as boundary condition, calculations with a simple dispersion model show the gradual decrease in the concentration with fetch in off-shore winds. In on-shore winds the surf-enhanced aerosol concentration is effective over only a short range, but nevertheless significant transmission losses may occur. Obviously, these conclusions apply only to the surf encountered during this specific experiment. The effects of the surf in other areas and other ambient conditions will be assessed from the analysis of data collected at a different location and in different conditions.

Supplement to physical exchanges at the air-sea interface: UK-SOLAS Field Measurements

This document is a supplement to “Physical Exchanges at the Air–Sea Interface: UK–SOLAS Field Measurements,” by Ian M. Brooks, Margaret J. Yelland, Robert C. Upstill-Goddard, Philip D. Nightingale, Steve Archer, Eric d’Asaro, Rachael Beale, Cory Beatty, Byron Blomquist, A. Anthony Bloom, Barbara J. Brooks, John Cluderay, David Coles, John Dacey, Michael DeGrandpre, Jo Dixon, William M. Drennan, Joseph Gabriele, Laura Goldson, Nick Hardman-Mountford, Martin K. Hill, Matt Horn, Ping-Chang Hsueh, Barry Huebert, Gerrit de Leeuw, Timothy G. Leighton, Malcolm Liddicoat, Justin J. N. Lingard, Craig McNeil, James B. McQuaid, Ben I. Moat, Gerald Moore, Craig Neill, Sarah J. Norris, Simon O’Doherty, Robin W. Pascal, John Prytherch, Mike Rebozo, Erik Sahlee, Matt Salter, Ute Schuster, Ingunn Skjelvan, Hans Slagter, Michael H. Smith, Paul D. Smith, Meric Srokosz, John A. Stephens, Peter K. Taylor, Maciej Telszewski, Roisin Walsh, Brian Ward, David K. Woolf, Dickon Young, and Henk Zemmelink (Bull. Amer. Meteor. Soc., 90, 629–644) • ©2009 American Meteorological Society • Corresponding author: Ian M. Brooks, Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom • E-mail: i.brooks@see.leeds.ac.uk • DOI:10.1175/2008BAMS2578.2

Satellite and ship-based lidar measurements of optical depth during EOPACE

The authors consider methods for obtaining quantitative data of the coastal marine atmospheric boundary layer (MABL). Satellite remote sensing is the only data source that can measure MABL properties in the coastal zone with the needed high spatial resolution. However, many of the uses of satellite data are qualitative. Quantitative satellite remote sensing methods need to be tested to provide littoral data. Ship-based aerosol and lidar backscatter measurements, aircraft-measured aerosol, and rawinsonde data obtained during the Electro-Optical Propagation Assessment in Coastal Environments (EOPACE) Intense Observing Periods (IOPs) provide an opportunity to compare satellite methods with in situ data. The purpose of the EOPACE program is to characterize the aerosol and boundary layer properties in the coastal zone and to determine if air mass parameters in various coastal locations can be derived, to a practical degree, from satellite imagery. The combination of satellite data with several in situ surface and aircraft data sets offers an excellent opportunity to monitor significant optical depth and aerosol changes in the coastal zone. In addition, quantitative comparisons can be made. The objective of this paper is to evaluate satellite-derived aerosol optical depths estimates using aircraft and ship-based aerosol measurements, a ship-based lidar and rawinsonde profiles of the MABL. Results from the April 1996 IOP are presented.

Influence of submicron aerosol composition upon atmospheric extinction in coastal areas

Measurements of sub-micron aerosol particles in southern California coastal areas during the Electro-Optical Propagation Assessment in Coastal Environments program indicate that not only particle concentrations but also the composition of the aerosol is highly variable due to the range of particular and pre-cursor gaseous sources present in the littoral zone. Frequently, in offshore flow, large quantities of soot carbon resulting from fossil fuel burning are mixed with pervasive sulphate aerosol particles, while in onshore flow, significant numbers of sea spray particles are present. At larger particle sizes, the aerosol spectrum may be dominated by sea spray particles produced by the action of the wind on the ocean surface at moderate and high wind speeds. This situation is further complicated along coasts where breaking surf provides an additional source of sea spray, and where offshore breezes may transport aeolian dusts from the land interior. These measurements demonstrate that land-sea breezes and other local meteorological processes give rise to substantial variations in aerosol characteristics on relatively small temporal and spatial scales and, from this knowledge of particulate composition, aerosol refractive indices and, hence, atmospheric extinctions at visible and IR wavelengths have been derived for various environmental conditions.

Variations in submicron aerosol composition during the EOPACE program

Observations of the size-differentiated composition of aerosol particles obtained during the EOPACE (Electro-Optical Propagation Assessment in Coastal Environments) Air Mass Characterisation Experiment in April 1996 are reported. These measurements were made on board the RV Point Sur along the southern California coast, with special emphasis on the Southern California Bight, and demonstrate the extreme variability ofboth aerosol composition and loadings within this region. A thermal analytical technique, which relies upon the fact that dominant aerosol species volatilise at characteristic temperatures, was utilised to determine aerosol composition and comprised a heater system coupled to a commercial optical particle counter. Accompanying measurements of soot carbon loadings were obtained by means of a commercial aethalometer and clearly demonstrated the impact of urban pollution upon this littoral region. This study formed one element ofthe Air Mass Characterisation Experiment which included the retrieval of aerosol optical depths from NOAA-14 sateffite overpasses ofthe region.