Lagrangian analysis of low altitude anthropogenic plume processing across the North Atlantic

Abstract

Abstract. The photochemical evolution of an anthropogenic plume from the New-York/Boston region during its transport at low altitudes over the North Atlantic to the European west coast has been studied using a Lagrangian framework. This plume, originally strongly polluted, was sampled by research aircraft just off the North American east coast on 3 successive days, and then 3 days downwind off the west coast of Ireland where another aircraft re-sampled a weakly polluted plume. Changes in trace gas concentrations during transport are reproduced using a photochemical trajectory model including deposition and mixing effects. Chemical and wet deposition processing dominated the evolution of all pollutants in the plume. The mean net photochemical O 3 production is estimated to be −5 ppbv/day leading to low O 3 by the time the plume reached Europe. Model runs with no wet deposition of HNO 3 predicted much lower average net destruction of −1 ppbv/day O 3 , arising from increased levels of NO x via photolysis of HNO 3 . This indicates that wet deposition of HNO 3 is indirectly responsible for 80% of the net destruction of ozone during plume transport. If the plume had not encountered precipitation, it would have reached Europe with Correspondence to: E. Real (elsa.real@aero.jussieu.fr) O 3 concentrations of up to 80 to 90 ppbv and CO between 120 and 140 ppbv. Photochemical destruction also played a more important role than mixing in the evolution of plume CO due to high levels of O 3 and water vapour showing that CO cannot always be used as a tracer for polluted air masses, especially in plumes transported at low altitudes. The results also show that, in this case, an increase in O 3 /CO slopes can be attributed to photochemical destruction of CO and not to photochemical O 3 production as is often assumed.

Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde Atmospheric Observatory

“…At a remote site such as Cape Verde, O 3 and CO enhancements are due to changes in air mass origin and mixing, rather than local emissions of CO and subsequent O 3 formation. Real et al, (2008) noted that the O 3 /CO ratio in a polluted air parcel decreases as it ages and is transported further from the CO and O 3 source. The remote low latitude marine boundary layer is generally a region of low nitrogen oxide levels and high sunlight and water vapour, and thus rapid photochemistry.…”

Global O<sub>3</sub>–CO correlations in a chemistry and transport model during July–August: evaluation with TES satellite observations and sensitivity to input meteorological data and emissions

“…Generally, a positive correlation in summer indicates strong photochemical production of O 3 downwind of polluted regions (Chin et al, 1994;Tsutsumi and Matsueda, 2000). A negative correlation indicates stratospheric influence (Parrish et al, 1998;Hsu et al, 2004), photochemical O 3 destruction (Fishman and Seiler, 1983;Parrish et al, 1998;Mao and Talbot, 2004), or chemical production of CO (Chin et al, 1994;Real et al, 2008). Small correlation coefficients and small linear regression slopes are indications of fresh pollution plumes that have not yet realized their O 3 production potential due to, for example, incomplete photochemical processes (Naja et al, 2003).…”

Modeling ozone plumes observed downwind of New York City over the North Atlantic Ocean during the ICARTT field campaign

“…Mao et al (2006) analyzed in-situ O 3 measurements obtained from semi-Lagrangian balloons in which high O 3 mixing ratios over the North Atlantic, compared to the northeastern US, were captured during the transport of urban plumes. Real et al (2008) used a Lagrangian analysis of the ICARTT measurements to show that urban plumes originating from the New York City (NYC)-Boston region reach Western Europe. Efficient transport of nitric acid (HNO 3 ), a major product of NO x oxidation in urban plumes (Trainer et al, 1995), can play an important role in maintaining O 3 levels in the plumes carried across the Atlantic through NO x regeneration and photochemical production (Neuman et al, 2006;Real et al, 2008).…”

“…Real et al (2008) used a Lagrangian analysis of the ICARTT measurements to show that urban plumes originating from the New York City (NYC)-Boston region reach Western Europe. Efficient transport of nitric acid (HNO 3 ), a major product of NO x oxidation in urban plumes (Trainer et al, 1995), can play an important role in maintaining O 3 levels in the plumes carried across the Atlantic through NO x regeneration and photochemical production (Neuman et al, 2006;Real et al, 2008). In those studies, efficient low-level long-range transport was attributed to the existence of an atmospheric inversion layer over the North Atlantic Ocean, which had been identified by previous measurements over the region that showed MBL heights less than ∼100 m (e.g.…”