Análisis de posibles fuentes de financiamiento

The comprehensive dataset allows to find any patterns in the typical routes of NO2

long-range transport and to determine the most common sources.

To find the typical routes – without assumptions from the determined backtrajectories – I employ the following method:

• Iterate over all verified plumes and project the tropospheric NO2 vertical column density of each member cell onto a global grid.

• Add the projections of all plumes.

• Count the number of days of valid observation for each cell and create a global map.

• Divide the a total tropospheric NO2 vertical column density map by the number of observations map.

So, the mean tropospheric NO2vertical column density in long-range transport events VCDLRT can be defined as:

VCDLRT(lat, lon) =



plumesVCDplume(lat, lon)

Nobservations(lat, lon) (7.3)

This gives an estimate of the typical NO2 long-range transport routes; it is an esti-mator for the mean tropospheric NO2 vertical column density observed in long-range transport events. As long-range transport events are frequent, the resulting map is smooth and gives an indication of the average flow of NO2 in long-range transports.

Multiple observations of individual long-range transports on different days are included in the data and lead to routes of longer lasting plumes to be adequately represented.

The resulting maps for individual seasons can be found in Figure 7.19. They show clear regional and seasonal differences in typical long-range transport routes with most of the long-range transport being observed in the mid-latitudes.

In the Northern Hemisphere, there are strong routes from the East Coast of the USA towards the North Atlantic, Greenland and the Arctic. There is also a route from

7.2 Statistical analysis

the East Coast towards Northern Canada in a giant arc as well as a less pronounced trajectory (due to short lifetimes) towards the tropics. Europe appears to emit long-range transports in all northern directions, with an especially pronounced route towards Greenland. Due to the convoluted coast-line, there is still significant NO2 from long-range transport visible in spring, located over the Baltic Sea and the North Sea. China exhibits routes in winter and autumn that lead to Taiwan and Japan, with a dominant arc leading back to Eastern Russia over the Sea of Okhotsk. There is also a very fragmented route leading from the Beijing area over the Pacific towards the West Coast of North America. In spring, most of these routes can still be seen, though at a strongly attenuated level. During summer, there is almost no long-range transport visible, due to the short lifetime of NO2 and missing frontal systems.

In the Southern Hemisphere, the only major emitter of NO2 long-range transport is South Africa. There is a very distinct band of high average NO2 long-range transport vertical column densities originating on the South African shore and dominantly leading out towards the Antarctic Circle (as far as GOME-2 / MetOp-A can observe it) and Australia. Further long-range transports are found near the shores of Argentina, but at a much lower frequency than for the four major emission regions. As most of these events also take place in winter, they appear to be linked to anthropogenic emission as well. Near Australia, however, long-range transport events appear to be far more rare and irregular than near the aforementioned emission regions. Most events are found in autumn (MAM), the main bush fire season. These two facts may indicate an origin in bush fires or other irregular emission events.

The arc-like routes – transporting NO2 back to their origin or adjacent regions – are common in the Northern Hemisphere and caused by circular winds around the cyclones lifting the NO2 from the planetary boundary layer to the free troposphere.

Plotting this map for all seasons combined but divided by plume age shows the typical plume movement (Figure 7.20). Young plumes are only located near the shores and starting in a rather narrow export band. Older plumes can (also) be found further off the shore and show higher scatter across the oceans. The oldest plumes can hardly be attributed to specific emission regions without backtrajectory calculations.

7.2.4 Sources

In the second step, I create an analogous map, in which the NO2 content of each cell is relocated to the determined source of the cell – the coordinates at which the backtra-jectory of the cell ends. Note, that all backtrajectories have the same temporal length:

the estimated plume age.

This map then gives an estimator of the mean tropospheric NO2 vertical column density that is emitted into long-range transport from this location. It serves as an indicator of the impact the region has on NO2 long-range transport: The higher the values, the stronger the impact.

As seen in Figure 7.21, there are four hot spots of long-range transport sources. These are the same regions that were identified earlier in Subsection 7.2.3: China, Central Europe, the East Coast of North America and South Africa. There are some fuzzy souces: Western Argentina and Uruguay appear to be a weak but rather regular emission region – centered on Buenos Aires and Montevideo – while Australia appears to be very

Figure 7.19: Seasonal maps of the mean vertical column density of NO2 observed in plumes associated to long-range transport events. Note that columns near Europe are always higher than columns near North America – at least partially due to its special geography. There is a clear seasonality, favoring long-range transport events during winter. There is more NO2in transports on the Northern Hemisphere, where most of the emissions take place.

Figure 7.20: Route map as in Figure 7.19 but divided by plume age instead of season.

Day 1 refers to plumes with an estimated age of 0–23 hours. Young plumes are typically located closer to shores while older plumes are distributed more evenly and do not show maxima very close to emission regions.

7 NO₂ long-range transport in GOME-2 data

Figure 7.21: Seasonal maps of the mean tropospheric NO2 vertical column density ob-served in plumes associated to long-range transport events, projected back to their sources as retrieved from the most likely backtrajectory.

irregular.

Most of the estimated source regions are a result of massive anthropogenic emissions due to industry and transportation. The lesser sources of long-range transported NO2 – Australia and Argentina – could be caused by irregular emission events such as biomass burning. Especially Australia shows most long-range transport during autumn (MAM) – the prime season for biomass burning.

There is a strong scatter of points around these sources. This is a result of the limited resolution of both input data and the meteorological input data used for the HYSPLIT_v4 computations of backtrajectories (compare Subsection 6.4.2). This scat-ter is inevitable and increases roughly exponentially with increasing duration of the backtrajectory – given by the plume age. Taking this scatter into account, it is sur-prising that the resulting sources are determined to be rather sharp. This is also an indication that false positive detections do not dominate over the impact of correct detections.

For the South African emission region, there is a bias in the determined emission region towards the East of the Highveld plateau. This might be due to the elevated topography and dominant downwinds when air from the plateau is moving towards the East. These would cause the backtrajectory selection procedure to prefer a younger plume whose trajectories are still better correlated. In principle this selection bais will always tend to select an origin slightly downwind of the actual origin, but it is most prominent in this particular topography.

7.2 Statistical analysis

Figure 7.22: The regions used for the statistical study. Only plumes are considered that were observed over the ocean in the filled rectangle and were found over land-masses in the open rectangle 24 hours earlier.