[1] Submicrometer sea salt aerosol (SSA) particles are routinely observed in the remote marine boundary layer (MBL); these aerosols include cloud condensation nuclei and so affect the earth's radiative balance. Here foams designed to mimic oceanic whitecaps were generated in the laboratory using a range of bubbling flow rates and aqueous media: unfiltered seawater, filtered seawater, artificial seawater, and mixtures of filtered and artificial seawater. The number and sizes of dried foam droplets in the particle diameter, D p , range 15-673 nm were measured. Particle size distributions for natural and artificial seawaters were unimodal with a dN/d logD p mode at D p % 100 nm (%200 nm at 80% RH). The foam droplet mode falls within the range of reported mode diameters (D p = 40-200 nm) for submicrometer SSA particles observed in the remote MBL. The present laboratory results were scaled up to estimate submicrometer SSA particle fluxes; this extrapolation supports the hypothesis that foam droplets are the most important source of SSA particles by number. The foam droplet flux from the oceans was estimated to be 980 cm À2 s À1 for a fractional white cap coverage, W, of 0.2%. These results compared well with foam droplet fluxes reported elsewhere. The origins of variability in foam droplet fluxes were also evaluated. Natural organic matter affected foam droplet flux by a factor of 1.5; this was less than (1) the effect of bubbling flow rate on foam droplet flux (factor of 5) and (2) the uncertainty in W (factor of 3-7).

Ultraviolet light (UV) combined with peroxy chemicals, such as H2O2 and peroxydisulfate (PDS), have been considered potentially highly effective disinfection processes. This study investigated the inactivation of Escherichia coli, bacteriophage MS2, and Bacillus subtilis spores as surrogates for pathogens under UV/H2O2 and UV/PDS conditions, with the aim to provide further understanding of UV-based advanced disinfection processes (ADPs). Results showed that one additional log of inactivation of E. coli was achieved with 0.3 mM H2O2 or PDS at 5.2 × 10(-5) Einstein·L(-1) photo fluence (at 254 nm) compared with UV irradiation alone. Addition of H2O2 and PDS greatly enhanced the inactivation rate of MS2 by around 15 folds and 3 folds, respectively, whereas the inactivation of B. subtilis spores was slightly enhanced. Reactive species responsible for the inactivation were identified to be •OH, SO4(·-), and CO3(·-) based on manipulation of solution conditions. The CT value of each reactive species was calculated with respect to each microbial surrogate, which showed that the disinfection efficacy ranked as •OH > SO4(·-) > CO3(·-) ≫ O2(·-)/HO2(·). A comprehensive dynamic model was developed and successfully predicted the inactivation of the microbial surrogates in surface water and wastewater matrices. The concepts of UV-efficiency and EE/O were employed to provide a cost-effective evaluation for UV-based ADPs. Overall, the present study suggests that it will be beneficial to upgrade UV disinfection to UV/H2O2 ADP for the inactivation of viral pathogens.

Sea‐salt aerosol (SSA) particles affect the Earth's radiative balance and moderate heterogeneous chemistry in the marine boundary layer. Using conventional and environmental transmission electron microscopes (ETEM), we investigated the hygroscopic growth and liquid‐layer compositions of particles generated from three types of aqueous salt solutions: sodium chloride, laboratory‐synthesized seawater (S‐SSA particles), and natural seawater (N‐SSA particles). Three levels of morphological change were observed with the ETEM as the laboratory‐generated particles were exposed to increasing relative humidity (RH). The first level, onset of observable morphological changes, occurred on average at 70, 48, and 35% RH for the NaCl, S‐SSA, and N‐SSA particles, respectively. The second level, rounding, occurred at 74, 66, and 57% RH for NaCl, S‐SSA, and N‐SSA particles, respectively. The third level, complete deliquescence, occurred at 75% RH for all particles. Collected ambient SSA particles were also examined. With the exception of deliquescence, they did not exhibit the same hygroscopic characteristics as the NaCl particles. The ambient particles, however, behaved most similarly to the synthesized and natural SSA particles, although the onset of morphological change was slightly higher for the S‐SSA particles. We used energy‐dispersive X‐ray spectrometry to study the composition of the liquid layer formed on the S‐SSA and N‐SSA particles. The layer was enriched in Mg, S, and O relative to the solid particle core. An important implication of these results is that MgSO4‐enriched solutions on the surface of SSA particles may be the solvents of many heterogeneous reactions.

Selenium has unique fate and transport through a coal-fired power plant because of high vapor pressures of oxide (SeO2) in flue gas. This study was done at full-scale on a 900 MW coal-fired power plant with electrostatic precipitator (ESP) and wet flue gas desulfurization (FGD) scrubber. The first objective was to quantify the partitioning of selenium between gas and condensed phases at the scrubber inlet and outlet. The second objective was to determine the effect of scrubber operation conditions (pH, mass transfer, SO2 removal) on Se removal in both particulate and vapor phases. During part of the testing, hydrated lime (calcium hydroxide) was injected upstream of the scrubber. Gas-phase selenium and particulate-bound selenium were measured as a function of particle size at the inlet and outlet of the scrubber. The total (both phases) removal of Se across the scrubber averaged 61%, and was enhanced when hydrated lime sorbent was injected. There was evidence of gas-to-particle conversion of selenium across the scrubber, based on the dependence of selenium concentration on particle diameter downstream of the scrubber and on thermodynamic calculations.

Isokinetic sampling, in which a subsample is extracted from the center of laminar aerosol flow, is routinely used to collect representative particles for analysis. Isokinetic sampling minimizes wall effects, including particle loss due to Brownian diffusion to the tube wall. This particle diffusion is analogous to the heat transfer problem originally posed by Graetz in 1883. Analytical solutions to the Graetz problem have been applied to calculate particle loss averaged over the entire main flow. However, these solutions overestimate diffusional particle loss near the center of the main flow. In the present solution, confluent hypergeometric functions are used to solve analytically for particle concentration as a function of radius. The solution is integrated near the center of the main flow to determine particle loss for isokinetically sampled aerosols. Sampling efficiencies valid down to nanometer-sized particles are presented in terms of dimensionless parameters. Diffusional particle loss for isokinetically sampled aerosol can be 1.8 times less than that from the main flow aerosol. The present results can be used to design isokinetic sampling systems and to assess particle loss in these systems. For 5 nm diameter particles sampled isokinetically from a laminar flow tube (0.318 cm tube radius, 10 m length) into an ultrafine condensation particle counter, sampling efficiency is strongly affected by main flow Reynolds number, Re; sampling efficiency increases from 4.9% at Re = 100 to 99% at Re = 1500.