Aircraft measurements over Europe of an air pollution plume from Southeast Asia – aerosol and chemical characterization

Abstract

Abstract. An air pollution plume from Southern and Eastern Asia, including regions in India and China, was predicted by the FLEXPART particle dispersion model to arrive in the upper troposphere over Europe on 24-25 March 2006. According to the model, the plume was exported from Southeast Asia six days earlier, transported into the upper troposphere by a warm conveyor belt, and travelled to Europe in a fast zonal flow. This is confirmed by the retrievals of carbon monoxide (CO) from AIRS satellite measurements, which are in excellent agreement with the model results over the entire transport history. The research aircraft DLR Falcon was sent into this plume west of Spain on 24 March and over Southern Europe on 25 March. On both days, the pollution plume was found close to the predicted locations and, thus, the measurements taken allowed the first detailed characterization of the aerosol content and chemical composition of an anthropogenic pollution plume after a nearly hemispheric transport event. The mixing ratios of CO, reactive nitrogen (NO y ) and ozone (O 3 ) measured in the Asian plume were all clearly elevated over a background that was itself likely elevated by Asian emissions: CO by 17-34 ppbv on average (maximum 60 ppbv) and O 3 by 2-9 ppbv (maximum 22 ppbv). Positive correlations existed between these species, and a O 3 / CO slope of 0.25 shows that ozone was formed in this plume, albeit with moderate efficiency. Nucleation mode and Aitken particles were suppressed in the Asian plume, whereas accumulation mode aerosols were strongly elevated and correlated with CO. The suppression of the nucleation mode was likely due to the large pre-existing aerosol surface of the transported larger particles. Supermicron particles, likely desert dust, were found in part of the Asian pollution plume and also in surrounding cleaner air. The aerosol light absorption coefficient was enhanced in the plume (average values for individual plume encounters Correspondence to: A. Stohl (ast@nilu.no) 0.25-0.70 Mm −1 ), as was the fraction of non-volatile Aitken particles. This indicates that black carbon (BC) was an important aerosol component. During the flight on 25 March, which took place on the rear of a trough located over Europe, a mixture of Asian pollution and stratospheric air was found. Asian pollution was mixing into the lower stratosphere, and stratospheric air was mixing into the pollution plume in the troposphere. Turbulence was encountered by the aircraft in the mixing regions, where the thermal stability was low and Richardson numbers were below 0.2. The result of the mixing can clearly be seen in the trace gas data, which are following mixing lines in correlation plots. This mixing with stratospheric air is likely very typical of Asian air pollution, which is often lifted to the upper troposphere and, thus, transported in the vicinity of stratospheric air.

An investigation of methods for injecting emissions from boreal wildfires using WRF-Chem during ARCTAS

“…Several previous studies have employed AIRS CO to investigate the horizontal extent of combustion products (e.g., Peffers et al, 2009;Zhang et al, 2008;Stohl et al, 2007). AIRS provides ∼70 percent coverage of the Earth's surface on a daily basis (McMillan et al, 2005).…”

“…This inclusion is important since many transport models rely on coarse horizontal scale (e.g., 45-200 km) global meteorological models for their transport parameters (e.g., Stohl et al, 2007;Damoah et al, 2004). Although these models generally have produced satisfactory results, global models do compound interpolation error both spatially and temporally and can produce nonphysical results within transport models (Stohl et al, 1995.…”

Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

“…Under such circumstances homogeneous nucleation of particles is theoretically possible, and has been observed (e.g., Perry and Hobbs, 1994;Hegg and Baker, 2009;Weigelt et al, 2009). Stohl et al (2007) in particular observed such behavior in SEA air transported to Europe.…”

“…Plumes are frequently shown in these papers to reach as far as Taiwan, including the free troposphere receptor site on Lulin Mountain (Wang et al, 2007;Wai et al, 2008;Lin et al, 2009), southern Japan (Tang et al, 2003a,b;Satake et al, 2004) and Hawaii ). Aircraft observations near Europe even identified one exceptionally large IC pollution and smoke event that had traversed 2/3 of the globe (Stohl et al, 2007).…”

Satellite perspective of aerosol intercontinental transport: From qualitative tracking to quantitative characterization

“…Saharan dust routinely reaches the Amazon, the Caribbean Sea and southeastern U.S. after sweeping over the Atlantic Ocean (Swap et al, 1992;Prospero, 1999;. Asian dust and pollution have long been observed in the western U.S. and beyond (Jaffe et al, 1999;Biscaye et al, 2000;VanCuren and Cahill, 2002;Grousset et al, 2003;Stohl et al, 2007). Microorganisms such as bacteria, fungi, and viruses can be transported along with dust aerosol (Griffin, 2007), raising additional health concern.…”