Intercontinental air pollution transport from North America to Europe: Experimental evidence from airborne measurements and surface observations

Abstract

During the airborne CONTRACE field experiment carried out in November 2001 a number of polluted layers of North American (NA) origin were observed in the free troposphere over Europe. For the first time, forecasts from a Lagrangian particle dispersion model were used to predict the NA pollution events and to direct a research aircraft very precisely into these polluted layers above Europe. Two of the NA pollution events are investigated here: one in detail (case 19 November) and a second more briefly (case 22 November). An exceptional result was that the first pollution plume could be traced with the model and trace gas measurements (airborne and surface) for a period of one week, from the source region over the eastern United States to its decay over the Alps. On 14–15 November a warm conveyor belt lifted the leading edge of the pollution plume over the eastern United States to the mid troposphere where it remained during the transport over the Atlantic. On 19 November the plume was intersected with the research aircraft over Scandinavia at an altitude between 2 and 4 km. Elevated CO (170), O3 (53), NOy (1.1), acetone (5.0), and SO2 (2.6) mixing ratios (nmol/mol) were measured. A positive O3-CO correlation was observed in the plume. The observations indicate that the enhanced levels of ozone were already produced near the source region over the eastern United States and not during the transit. In the next days one branch of the plume then turned to the south and descended to ground level over the Alpine region. Elevated O3 (54 nmol mol 1) and CO (168 nmol/mol) were observed at the mountain site Zugspitze (southern Germany) during two days. At the Arosa Alpine site in Switzerland the highest daily ozone means of November 2001 were observed during this event

Changes in the Chemistry of Small Irish lakes

“…As such, non-marine (nm) SO 4 2-deposition is low (\25 mmol c m -2 year -1 [one mole of charge (mol c ) is numerically equal to one equivalent (eq)]) compared to other industrial regions of Europe . Nonetheless, Ireland receives acidifying compounds associated with easterly air masses from Western Europe (Bowman and McGettigan 1994) and, to a lesser extent, pollutants carried in western air masses from North America (Huntrieser et al 2005). The impact of acidic deposition has been a potential concern since the 1980s (Bailey et al 1986) owing to the preponderance of surface waters in acid-sensitive regions (Bowman 1991;Flower et al 1994).…”

Synoptic influences on springtime tropospheric O<sub>3</sub> and CO over the North American export region observed by TES

“…Pollutants may also be transported from the continental boundary layer in a warm conveyor belt (WCB) of a synoptic-scale mid-latitude cyclone into streams of fast moving middle and upper tropospheric westerly winds (Eckhardt et al, 2004;Crielson et al, 2003;Stohl et al, 2003a). Some WCBs originating over North America can transport O 3 and precursors to the free troposphere over Europe within 4-5 days (Stohl et al, 1999(Stohl et al, , 2003a where descending motions carry them back toward the surface causing groundlevel O 3 mixing ratios to rise, but so far this has only been observed at high elevation sites in the Alps (Huntrieser et al, 2005). However, the same cyclones responsible for lofting O 3 -forming anthropogenic pollutants from the continental boundary layer to the free troposphere may also mix down O 3 of stratospheric origin, which inevitably complicates the quantification of the tropospheric O 3 budgets (Cooper et al, 2001(Cooper et al, , 2002Moody et al, 1996;Merrill et al, 1996;Oltmans et al, 1996;Polvani and Esler, 2007).…”

Boundary‐layer ventilation by baroclinic life cycles

“…Many more combined observational and modelling studies of intercontinental transport between North America and Europe (e.g. Bethan et al, 1998;Cooper et al, 2001;Li et al, 2002;Stohl et al, 2003;Huntrieser et al, 2005) and across the Pacific basin (e.g. Fuelberg et al, 2003;Cooper et al, 2004;Mari et al, 2004) have been conducted and results show that WCBs are capable of transporting pollution large distances in both ocean basins.…”