ARM Southern Great Plains Site Observations of the Smoke Pall Associated with the 1998 Central American Fires

Abstract

Drought-stricken areas of Central America and Mexico were victimized in 1998 by forest and brush fires that burned out of control during much of the first half of the year. Wind currents at various times during the episode helped transport smoke from these fires over the Gulf of Mexico and into portions of the United States. Visibilities were greatly reduced during favorable flow periods from New Mexico to south Florida and northward to Wisconsin as a result of this smoke and haze. In response to the reduced visibilities and increased pollutants, public health advisories and information statements were issued by various agencies in Gulf Coast states and in Oklahoma. This event was also detected by a unique array of instrumentation deployed at the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program Southern Great Plains Cloud and Radiation Testbed and by sensors of the Oklahoma Department of Environmental Quality/Air Quality Division. Observations from these measurement devices suggest elevated levels of aerosol loading and ozone concentrations during May 1998 when prevailing winds were favorable for the transport of the Central American smoke pall into Oklahoma and Kansas. In particular, aerosol extinction profiles derived from the ARM Raman lidar measurements revealed large variations in the vertical distribution of the smoke.

Sources of carbonaceous aerosols over the United States and implications for natural visibility

“…Figure 1 shows the resulting annual OC emissions from biomass burning in North and Central America for 1997-2000 as well as the climatological mean. An ENSO-related drought resulted in catastrophic wildfires in the tropical forests of southern Mexico and Central America in 1998 [Peppler et al, 2000]. Canadian fire emissions were also unusually large in 1998.…”

Natural Background Visibility and Regional Haze Goals in the Southeastern United States

“…Effects of large wildfires in Northwestern Canada have been observed on air pollutant concentrations in Tennessee, 21 and transport and impact of smoke from wildfires and biomass burning in Southern Mexico and Central America have been observed in the central and southeastern portions of the United States. 22,23 The contributions of natural fires to background carbon concentrations have just begun to be quantified. They are, of course, highly episodic at any given location.…”

Characteristics and direct radiative effect of mid-latitude continental aerosols: the ARM case

“…This relative humidity control minimizes the effects of changing relative humidity on the measurements and provides a reference point where the properties of ambient aerosols are measured. Bergin et al (1997) and Peppler et al (2000) reported that losses of ammonium nitrate (and less volatile species) due to evaporation under the sampling conditions used in ARM aerosol observing system are small. Size-segregated measurements of σ s and σ a were made through a switch impactor system, such that only particles with aerodynamic diameter D p smaller than 10 µm were sampled.…”

“…Lowest K + concentrations are recorded in winter. Although local field burning occurs in the vicinity of the SGP many times in the year, these activities are most pronounced in May, June and July (Peppler et al, 2000;Iziomon and Lohmann, 2003). Wind blown soil dust contains a significant amount of Ca, Mg, Al, Fe, Ti and Si (Barie and Barrie 1990, Malm et al 1996.…”