Aug 15, 2000 - dust seen by mariners as they approach Asia has long ... by the NASA P-3B flying from California to Hawaii on March 11, 1999. A dust layer ...
Seasonal changes in pollutant transport to the North Pacific' the relative importance of Asian and European sources.
ReginaldE. Newell and Mathew J. Evans Department of Earth, Atmospheric and Planetary Sciences,MassachusettsInstitute of Technology
Abstract.
The
industrialization
of south-east
Asia in-
vokes interest in the export path of the associatedpollution into the global atmosphere. During the winter the meteorology of this area is dominated by the Siberian anticyclone. Polluted air is typically kept in the planetary boundary layer by the large-scalesubsidence and moved
southwards.
This
contrasts
with
troposphere. An example of this influence was found by the NASA P-3B flying from California to Hawaii on March 11, 1999. A dust layer was noted at 31øN 122øW at 4.8kin, not far from the Californian coast.
ElevatedCO concentrations (230 ppbv) and C2Hu (900 pptv) werefound. The ratio of thesespeciesof about 4
the
is close to valuesfound previously in the South Pacific summer when it can be lifted to the upper troposphere due to biomassburning [Blakeet al., 1999]. Back traand transported across the Pacific by the aloft. This jectoriesshowedthat the sourceof this layer was China seasonalvariation is investigated using trajectory cal- rather than the more intuitively obvious source of Calculations. Then the influence of pollution from the Eu- ifornia. ropean region on south-eastAsia is investigated. During the winter up to 40% of the troposphericair enter- Destination of the south-east Asian ing south-eastAsia may have been polluted by Europe. pollution Finally, we propose an extended monitoring program over central Asia to separate south-east Asian polluTo try to understandthe destinationof the pollution tion fi'om the general pollution found in the Northern produced in south-eastAsia, forward trajectories have Hemisphere, and, to understand the effects of this in- been calculated for each month from December 1996 to dustrialization.
November 1997 originatingfrom the five industrialized Chinesecities shownin Figure 1. Although the choice of this year is arbitary the year doesnot seem that unusual. The mean sea level pressurebetween December
Introduction The
influence
of south-east
Asia
on the Pacific
at-
mosphere has been known for some time. Atmospheric
dust seenby mariners as they approachAsia has long been noted in their logbooks and summaries of these results
showed maximum
occurrences
of dust detection
in the springseason [McDonald,1938]. More objective analysis of this mineral dust was achieved by an island monitoring network in the North Pacific tropics
andsubtropics[Prosperoet al., 1989]and againshowed 'evidencefor a late winter-spring maximum in the dust deposits and an Asian source. Radon-rich air has been
measured(from aircraft) in the upper tropospherea few hundredkilometerswest of California [Kritz et al., 1983]. Trajectorycalculationssuggested that this air originated from the atmospheric lower levels over China during the summer. Recent attention has emphasizedthis region'sability to export photochemically
ß
active pollutant species(oxidesof nitrogen,hydrocarbons,carbonmonoxide)[Berntsenet al., 1999]and the subsequentperturbation to the photochemistry of the
