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

Abstract

Abstract. Transport and chemical transformation of welldefined New York City (NYC) urban plumes over the North Atlantic Ocean were studied using aircraft measurements collected on 20-21 July 2004 during the ICARTT (International Consortium for Atmospheric Research on Transport and Transformation) field campaign and WRF-Chem (Weather Research and Forecasting-Chemistry) model simulations. The strong NYC urban plumes were characterized by carbon monoxide (CO) mixing ratios of 350-400 parts per billion by volume (ppbv) and ozone (O 3 ) levels of about 100 ppbv near New York City on 20 July in the WP-3D in-situ and DC-3 lidar aircraft measurements. On 21 July, the two aircraft captured strong urban plumes with about 350 ppbv CO and over 150 ppbv O 3 (∼160 ppbv maximum) about 600 km downwind of NYC over the North Atlantic Ocean. The measured urban plumes extended vertically up to about 2 km near New York City, but shrank to 1-1.5 km over the stable marine boundary layer (MBL) over the North Atlantic Ocean. The WRF-Chem model reproduced ozone formation processes, chemical characteristics, and meteorology of the measured urban plumes near New York City (20 July) and in the far downwind region over the North Atlantic Ocean (21 July). The quasi-Lagrangian analysis of transport and chemical transformation of the simulated NYC urban plumes using WRF-Chem results showed that the pollutants can be efficiently transported in (isentropic) layers in the lower atmosphere (<2-3 km) over the Correspondence to: S.-H. Lee (nihil93@snu.ac.kr) North Atlantic Ocean while maintaining a dynamic vertical decoupling by cessation of turbulence in the stable MBL. The O 3 mixing ratio in the NYC urban plumes remained at 80-90 ppbv during nocturnal transport over the stable MBL, then grew to over 100 ppbv by daytime oxidation of nitrogen oxides (NO x = NO + NO 2 ) with mixing ratios on the order of 1 ppbv. Efficient transport of reactive nitrogen species (NO y ), specifically nitric acid (HNO 3 ), was confirmed through the comparison of the CO/NO y ratio in photochemically fresh and aged NYC plumes, implying the possibility of long-range transport of O 3 over the stable MBL over the North Atlantic Ocean in association with NO x regeneration mechanism. The impact of chemical initial and boundary conditions (IC/BCs) on modelled O 3 urban plumes was investigated in terms of the background O 3 level and the vertical structure of the urban plumes. Simulations with dynamic ("time-variant") chemical IC/BCs enhanced the O 3 level by 2-12 ppbv on average in the atmospheric layer below 3 km, showing better agreement with the observed NYC plumes and biomass-burning plumes than the simulation with prescribed static IC/BCs. The simulation including MOZART-4 chemical IC/BCs and Alaskan/Canadian wildfire emissions compared better to the observed O 3 profiles in the upper atmospheric layer (>∼3 km) than models that only accounted for North American anthropogenic/biogenic and wildfire contributions to background ozone. The comparison between models and observat...

Meteorological factors controlling low-level continental pollutant outflow across a coast

“…The tracer distribution shown is very similar to the distribution of ozone simulated by WRF-Chem (and averaged below 1700 m) that is shown in Fig. 9 of Lee et al (2011). Note that here a log scale is used to pick up the weaker concentrations further offshore.…”

“…However, there were marked episodes of cross-coastal pollutant transport, some of which were observed by research aircraft as the air crossed the Atlantic to the Azores and Europe (Methven et al, 2006;Owen et al, 2006). Chemical processing following air masses for several days during these ICARTT Lagrangian cases has been examined in detail by Real et al (2008); Lee et al (2011);Cain et al (2012); Davis et al (2012).…”

“…They named it the ICARTT Lagrangian Case 3, and it has been used to examine long-range transport and chemical transformation (Real et al, 2008;Cain et al, 2012). The near-range chemical evolution of the air mass has been examined by several authors including Lee et al (2011) and Davis et al (2012). Here, segments of three NOAA WP-3D flights following the air mass on consecutive days are used to compare the time evolution of observed vertical profiles of trace gases with the idealised tracer simulation.…”

“…The flight tracks on 20 and 21 July are coloured by CO mixing ratio in Figs. 4a and 5a in Lee et al (2011). Their analysis focuses on the evolution of an air mass they label the "New York Plume" which was characterised by the highest concentration of pollution observed on those flights.…”

Quantification of chemical and physical processes influencing ozone during long-range transport using a trajectory ensemble

“…5. Lee et al (2011) simulated the first two days of transport in case 3 using WRF-Chem, a mesoscale numerical weather prediction model coupled with chemistry, run with nested domains going up to 9 km horizontal grid spacing around the eastern seaboard region, where the flight on 20 July took place. They experimented with different initial and background chemical conditions (IC/BCs), and found that their choice of IC/BCs played an important role in determining the modelled O 3 profile.…”