Lagrangian Dispersion Model FLEXPART Research Articles

It is snowing microplastics in Western Siberia

The atmosphere is an important transport medium for polymeric anthropogenic particles such as microplastics (MPs). The analysis of particles deposited on the snowpack enables monitoring the abundance and transport of MPs and semi-synthetic fibers. In the current study, the abundance of MPs and man-made textile fibers in deposited snow in Western Siberia, Russia, was investigated in a large area ranging from the Altai Mountains (52°01″N) to the Arctic Circle (66°30″N). Rayon fibers accounted for 44% of all detected particles, while the remaining 56% were MPs made of PET, PA, PC, PP and other plastics. The highest number of MPs and fibers per unit area was 2817 ± 915 items m−2 with an estimated daily deposition rate of 25.8 items m−2 d−1. The maximum calculated mass particle load was 4444 ± 1530 mg m−2 or 34.9 ± 12 mg L−1 of melted snow. Particle concentrations in snow were generally higher in the southern parts of Western Siberia but did not significantly correlate with population density.The Lagrangian dispersion model FLEXPART was used to estimate the geographical patterns of potential sources of the fibers detected in the snow in Western Siberia. Our analysis shows that particles can reach the sampling sites via both short-range and long-range atmospheric transport, including the possibility of cross-border transport for the smaller particle sizes.

How marine emissions of bromoform impact the remote atmosphere

Abstract. It is an open question how localized elevated emissions of bromoform (CHBr3) and other very short-lived halocarbons (VSLHs), found in coastal and upwelling regions, and low background emissions, typically found over the open ocean, impact the atmospheric VSLH distribution. In this study, we use the Lagrangian dispersion model FLEXPART to simulate atmospheric CHBr3 resulting from assumed uniform background emissions, and from elevated emissions consistent with those derived during three tropical cruise campaigns. The simulations demonstrate that the atmospheric CHBr3 distributions in the uniform background emissions scenario are highly variable with high mixing ratios appearing in regions of convergence or low wind speed. This relation holds on regional and global scales. The impact of localized elevated emissions on the atmospheric CHBr3 distribution varies significantly from campaign to campaign. The estimated impact depends on the strength of the emissions and the meteorological conditions. In the open waters of the western Pacific and Indian oceans, localized elevated emissions only slightly increase the background concentrations of atmospheric CHBr3, even when 1∘ wide source regions along the cruise tracks are assumed. Near the coast, elevated emissions, including hot spots up to 100 times larger than the uniform background emissions, can be strong enough to be distinguished from the atmospheric background. However, it is not necessarily the highest hot spot emission that produces the largest enhancement, since the tug-of-war between fast advective transport and local accumulation at the time of emission is also important. Our results demonstrate that transport variations in the atmosphere itself are sufficient to produce highly variable VSLH distributions, and elevated VSLHs in the atmosphere do not always reflect a strong localized source. Localized elevated emissions can be obliterated by the highly variable atmospheric background, even if they are orders of magnitude larger than the average open ocean emissions.

Variability of moisture sources in the Mediterranean region during the period 1980-2000

In this study, seasonal and interannual variability of the main atmospheric moisture sources over eight regions in the Mediterranean basin were investigated along a 21 year period. The Lagrangian dispersion model FLEXPART, developed by Stohl and James [2004, 2005], was applied to identify the contribution of humidity to the moisture budget of each region. This methodology is used to compute budgets of evaporation minus precipitation (E-P) by calculating changes in the specific humidity along backward trajectories, for the preceding 10 day periods. The results show clear seasonal differences in the moisture sources between wet and dry seasons. The Western Mediterranean Sea is the dominant moisture source for almost all the regions in the Mediterranean basin during the wet season, while the local net evaporation dominates during the dry season. The highest interannual variability is found in contributions to the Iberian Peninsula, Italy, and the Eastern Mediterranean. It is seen that the role of teleconnections is more limited than for the precipitation recorded in the region.

Dimethylsulphide (DMS) emissions from the western Pacific Ocean: a potential marine source for stratospheric sulphur?

Abstract. Sea surface and atmospheric measurements of dimethylsulphide (DMS) were performed during the TransBrom cruise in the western Pacific Ocean between Japan and Australia in October 2009. Air–sea DMS fluxes were computed between 0 and 30 μmol m−2 d−1, which are in agreement with those computed by the current climatology, and peak emissions of marine DMS into the atmosphere were found during the occurrence of tropical storm systems. Atmospheric variability in DMS, however, did not follow that of the computed fluxes and was more related to atmospheric transport processes. The computed emissions were used as input fields for the Lagrangian dispersion model FLEXPART, which was set up with actual meteorological fields from ERA-Interim data and different chemical lifetimes of DMS. A comparison with aircraft in situ data from the adjacent HIPPO2 campaign revealed an overall good agreement between modelled versus observed DMS profiles over the tropical western Pacific Ocean. Based on observed DMS emissions and meteorological fields along the cruise track, the model projected that up to 30 g S per month in the form of DMS, emitted from an area of 6 × 104 m2, can be transported above 17 km. This surprisingly large DMS entrainment into the stratosphere is disproportionate to the regional extent of the area of emissions and mainly due to the high convective activity in this region as simulated by the transport model. Thus, if DMS can cross the tropical tropopause layer (TTL), we suggest that the considerably larger area of the tropical western Pacific Ocean can be a source of sulphur to the stratosphere, which has not been considered as yet.

Perturbation of the European free troposphere aerosol by North American forest fire plumes during the ICARTT-ITOP experiment in summer 2004

Abstract. During the ICARTT-ITOP Experiment in summer 2004 plumes from large wildfires in North America were transported to Central Europe at 3–8 km altitude above sea level (a.s.l.). These plumes were studied with the DLR (Deutsches Zentrum fuer Luft- und Raumfahrt) research aircraft Falcon which was equipped with an extensive set of in situ aerosol and trace gas instruments. Analyses by the Lagrangian dispersion model FLEXPART provided source regions, transport times and horizontal extent of the fire plumes. Results from the general circulation model ECHAM/MADE and data from previous aerosol studies over Central Europe provided reference vertical profiles of black carbon (BC) mass concentrations for year 2000 conditions with forest fire activities below the long-term average. Smoke plume observations yielded a BC mass fraction of total aerosol mass with respect to PM 2.5 of 2–8%. The ratio of BC mass to excess CO was 3–7.5 mg BC (g CO)−1. Even after up to 10 days of atmospheric transport, both characteristic properties were of the same order as for fresh emissions. This suggests an efficient lifting of BC from forest fires to higher altitudes with only minor scavenging removal of particulate matter. Maximum aerosol absorption coefficient values were 7–8 Mm−1 which is about two orders of magnitude above the average European free tropospheric background value. Forest fire aerosol size distributions were characterised by a strong internally mixed accumulation mode centred at modal diameters of 0.25–0.30 µm with an average distribution width of 1.30. Nucleation and small Aitken mode particles were almost completely depleted.