Exchange of polycyclic aromatic hydrocarbons among the atmosphere, water, and sediment in coastal embayments of southern California, USA.

The present study investigated cross-media transport between both the sediment and the water column and between the water column and the atmosphere, to understand the role of each compartment as a source or a sink of polycyclic aromatic hydrocarbons (PAH) in southern California, USA, coastal waters. Concentrations of PAH were measured in the atmosphere, water column, and sediment at four water-quality-impaired sites in southern California: Ballona Creek Estuary, Los Angeles Harbor, Upper Newport Bay, and San Diego Bay. These concentrations were used to calculate site-specific sediment-water and atmosphere-water exchange fluxes.

Atmospheric dry deposition of trace metals in the coastal region of Los Angeles, California, U.S.A.

Emissions of trace metals to the atmosphere and subsequent deposition, either directly to a waterbody surface or indirectly to the watershed as washoff during rainfall, represents a potential source of contamination to surface waters near urban centers. The present study provides measurements of atmospheric concentrations of particle-bound trace metals, and it estimates the dry deposition mass loading of trace metals in coastal watersheds in the Los Angeles, California, USA, air basin. Coarse-particle atmospheric concentrations of metals were measured seasonally using a Noll Rotary Impactor at six urban sites and one nonurban site.

The permeability of synthetic fractal aggregates with realistic three-dimensional structure.

The permeability of fractal porous aggregates with realistic three-dimensional structure is investigated theoretically using model aggregates composed of identical spherical primary particles. Synthetic aggregates are generated by several techniques, including a lattice-based method, simulation of aggregation by differential settling and turbulent shear, and the specification of simple cubic structures, resulting in aggregates characterized by the number of primary particles, solid fraction, characteristic radius, and fractal dimension. Stokesian dynamics is used to determine the total hydrodynamic force on and the distribution of velocity within an aggregate exposed to a uniform flow.

Contribution of trace metals from atmospheric deposition to stormwater runoff in a small impervious urban catchment.

The contribution of atmospheric deposition to emissions of trace metals in stormwater runoff was investigated by quantifying wet and dry deposition fluxes and stormwater discharges within a small, highly impervious urban catchment in Los Angeles. At the beginning of the dry season in spring 2003, dry deposition measurements of chromium, copper, lead, nickel, and zinc were made monthly for 1 year. Stormwater runoff and wet deposition samples also were collected, and loading estimates of total annual deposition (wet+dry) were compared with annual stormwater loads.

Aggregate formation and collision efficiency in differential settling.

A new method of application of Stokesian dynamics, which can efficiently simulate movements of up to 500 particles with interparticle interactions in reasonable computational times, has been developed for the purpose of investigating particle-cluster aggregation in aqueous systems. The method is applied to monodisperse non-Brownian spherical particles aggregating in differential settling, while repulsive colloidal interaction is presumed to be negligible, so that a minimum separation distance can represent the attractive van der Waals force. The final aggregates formed by this algorithm, composed of 300 primary particles, have a common fractal dimension of approximately 2.