Air Pollution Processing by Radiation Fogs

Abstract

Several fog episodes occurred in California's San Joaquin Valley during winter 2000/2001.Measurements revealed the fogs to generally be less than 50 m deep, but to contain high liquid water contents (frequently exceeding 200 mg/m 3 ) and large droplets. The composition of the fog water was dominated by ammonium (median concentration= 608 μN), nitrate (304 μN), and organic carbon (6.9 ppmC), with significant contributions also from nitrite (18 μN) and sulfate (56 μN). Principal organic species included formate (median concentration= 32 μN), acetate (31 μN), and formaldehyde (21 μM). High concentrations of ammonia resulted in high fog pH values, ranging between 5.8 and 8.0 at the core measurement site. At this high pH aqueous phase oxidation of dissolved sulfur dioxide and reaction of S (IV) with formaldehyde to form hydroxymethanesulfonate are both important processes. The fogs are also effective at scavenging and removal of airborne particulate matter. Deposition velocities for key solutes in the fog are typically of the order of 1-2 cm/s, much higher than deposition velocities of precursor accumulation mode aerosol particles. Variations were observed in deposition velocities for individual constituents in the order NO 2 − >fogwater>NH 4 + >TOC ∼ SO 4 2− >NO 3 − . Nitrite, observed to be enriched in large fog drops, had a deposition velocity higher than the average fogwater deposition velocity, due to the increase in drop settling velocity with size. Species enriched in small fog drops (NH 4 + , TOC, SO 4 2− , and NO 3 − ) all had deposition velocities smaller than observed for fogwater. Typical boundary layer removal rates for major fog solute species were estimated to be approximately 0.5-1 μg m −3 h −1 , indicating the important role regional fogs can play in reducing airborne pollutant concentrations.

Real-time secondary aerosol formation during a fog event in London

“…Several studies have reported sulphate production by fog/clouds (Laj et al, 1997). However, recent measurements of fog sample composition (Herckes et al, 2007a) show domination by nitrogen species, with ammonium and nitrate being the most abundant compounds. Fog droplets were found to have a pH well above 6, showing a significant decrease in fog concentration of sulphate and increase in fog pH in comparison to samples taken before the 1980s.…”

A Comparative Study on Fog and Dew Water Chemistry at New Delhi, India

“…The chemical composition of two is a cumulative outcome of gas-liquid-solid heterogeneous interactions. However, fog chemistry is influenced by number and composition of the particles, gaseous species (Herckes et al, 2007;Lekouch et al, 2011) as well as by the moisture content and temperature in ambient atmosphere. Dew water chemistry is also influenced by nature of surface on which it is formed (Beysens et al, 2006;Lekouch et al, 2010).…”

“…Fog chemistry has been widely studied at California and other locations of USA by Collett et al (2008Collett et al ( , 2002Collett et al ( , 1999; Herckes et al (2007). They have studied chemical composition, organic acids and buffering capacities of fog water.…”

The pollutants in rime and fog water and in air at Milesovka Observatory (Czech Republic)

“…1995; Elias et al 1995;Mindas & Skvarenina 1995;Skvareninova & Skvarenina 2000;Elbert et al 2000;Acker et al 2002;Migala et al 2002;Herckes et al 2007;Zapletal et al 2007;Mihalikova et al 2008). We have been concerned with these problems in our previous work for example , Fisak et al (2002, Fisak et al ( , 2006a.…”