Abstract
Abstract. Based on a 10-yr simulation with the global air quality modeling system GEM-AQ/EC, the northern hemispheric aerosol transport with the inter-annual and seasonal variability as well as the mean climate was investigated. The intercontinental aerosol transport is predominant in the zonal direction from west to east with the ranges of inter-annual variability between 14% and 63%, and is 0.5–2 orders of magnitude weaker in the meridional direction but with larger inter-annual variability. The aerosol transport is found to fluctuate seasonally with a factor of 5–8 between the maximum in late winter and spring and the minimum in late summer and fall. Three meteorological factors controlling the intercontinental aerosol transport and its inter-annual variations are identified from the modeling results: (1) Anomalies in the mid-latitude westerlies in the troposphere. (2) Variations of precipitation over the intercontinental transport pathways and (3) Changes of meteorological conditions within the boundary layer. Changed only by the meteorology, the aerosol column loadings in the free troposphere over the source regions of Europe, North America, South and East Asia vary inter-annually with the highest magnitudes of 30–37% in January and December and the lowest magnitudes of 16–20% in August and September, and the inter-annual aerosol variability within the boundary layer influencing the surface concentrations with the magnitudes from 6% to 20% is more region-dependent. As the strongest climatic signal, the El Niño-Southern Oscillation (ENSO) can lead the anomalies in the intercontinental aerosols in El Niño- and La Niña-years respectively with the strong and weak transport of the mid-latitude westerlies and the low latitude easterlies in the Northern Hemisphere (NH).
Highlights
Intercontinental transport of air pollution has been identified by a wealth of evidence observed from the ground, aircraft and satellites (HTAP, 2010)
The intercontinental aerosol transport is dominant in the eastward direction for all the East Asia (EA), North America (NA), EU- and South Asia (SA)-regions, and the transport in the meridional direction is 0.5–2 orders of magnitude weaker but with more significant interannual variability
The eastward transport across the low latitude SA-region is 2–4 times less compared to the midlatitude EA, NA- and EU-regions
Summary
Intercontinental transport of air pollution has been identified by a wealth of evidence observed from the ground, aircraft and satellites (HTAP, 2010). The inter-annual variability at receptor sites is controlled by the tempospatial changes of emission sources and the variations of atmospheric circulations or weather and climate patterns over the S-R regions and the transport pathways. This complicated feature is difficult to characterize from observations. To quantify the overall importance of hemispheric transport for aerosols, a single year simulation cannot evaluate the influence of inter-annual variability in meteorology on the SR relationships via changes in the intercontinental transport pathways for the HTAP.
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