On the formation and persistence of superfog in woodland smoke

Abstract

Dense fogs, comparable to historical fogs in England, have been implicated in numerous roadway accidents in the southern United States. Many of the fogs have occurred in association with prescribed burning. Direct measurements of superfog (fog reducing visibility to less than 3 m) were taken during burning of forest litter on 22 March 2003. Visibility was measured at 0.1 m implying an extinction coefficient of 39 120 km −1 . The number of condensation nuclei required for fog to produce the observed visibility was about 1% of the number of particles released in wood smoke as reported in the literature. A recursive non-gradient mixing model shows (1) maximum excess liquid water (LWC) released was approximately 7.0 g kg −1 , 23 times the LWC in natural fog, (2) superfog can form at the site of combustion then continue to form as it drifts downwind, and (3) superfog can modify air mass stability near the ground and persist for hours until dispersed by changing wind conditions or by solar heating after sunrise. Published in

Modeling Smoke Plume-Rise and Dispersion from Southern United States Prescribed Burns with Daysmoke

“…A cumulus cloud forms when the moisture (mixing ratio) within a rising, entraining turret exceeds the saturation mixing ratio calculated for the turret temperature. Both turret temperature and mixing ratio are calculated via Equation (5). The entire turret is assumed to be saturated.…”

“…Smoke from these burns poses a threat-either as a nuisance, visibility, or transportation hazard [4,5], and/or as a health hazard [6]. The hazard can be local and/or regional depending on the number of prescribed burns being conducted on a given day.…”

Air quality policy and fire management responses addressing smoke from wildland fires in the United States and Australia

“…More isolated research has also aided fire managers. In the southeastern US, late winter is well suited for the application of emissions reductions techniques, but also a time when smoke can contribute to formation of dense fogs (Achtemeier 2009) that can cause highway fatalities (Achtemeier 2002). Fog formation research led to the development of new predictive tools for fire managers .…”

Particulate and trace gas emissions from prescribed burns in southeastern U.S. fuel types: Summary of a 5-year project

“…Emissions characterization for both gases and particles is needed to determine potential impacts of prescribed burning on nutrient cycling, atmospheric albedo, human health, and visibility e.g. [13,19,20]. The southern U.S. was one of the first regions of the country to examine the impact of prescribed burning on air quality in both the laboratory and in the field [9,21]; recent advances in measurement devices provided an opportunity to improve knowledge of emissions using state-of the art instrumentation capable of real-time and in situ emissions measurements.…”