The Lagrangian particle dispersion model FLEXPART was used to construct a global data set of 1.4 million continuous trajectories. At the model start, particles were distributed homogeneously in the ...atmosphere and were then transported for 5.5 years using both resolved winds from European Centre for Medium‐Range Weather Forecasts analyses and parameterized turbulent and convective transport. On the basis of this data set, a climatology of transport in and to the Arctic was developed. It was found that the time air resides continuously north of 70°N, called its Arctic age, is highest near the surface in the North American sector of the Arctic. North of 80°N and near the surface, the mean Arctic age of air is about 1 week in winter and 2 weeks in summer. It decreases rapidly with altitude to about 3 days in the upper troposphere. In the most isolated regions of the Arctic, air is exposed to continuous darkness for, on average, 10–14 days in December. Transport from the stratosphere to the lower troposphere is much slower in the Arctic than in the middle latitudes. In the central Arctic, for instance, the probability that air near the surface was transported from the stratosphere within 10 days is only about 1% in winter and 0.3% in summer. Air pollution can be transported into the Arctic along three different pathways: low‐level transport followed by ascent in the Arctic, low‐level transport alone, and uplift outside the Arctic, followed by descent in the Arctic. Only this last pathway is frequent for pollution originating from North America and Asia, whereas European pollution can follow all three pathways in winter, and pathways one and three in summer. Sensitivities of Arctic air masses to emissions of air pollutants, based on transport alone, were calculated for times of up to 30 days before the air masses reached the Arctic. They were highest over Siberia and Europe in winter and over the oceans in summer. Using an inventory for anthropogenic black carbon (BC) emissions, it was found that near the surface and for transport timescales of 5 and 10 days, BC source contributions from south Asia are only 1.6% and 10%, respectively, of the corresponding European values, despite much higher emissions in south Asia. Using an inventory for BC emissions from forest fires, BC source contributions to the Arctic, particularly from fires in Siberia, were larger than anthropogenic BC source contributions in summer in years of average burning.
Abstract
In recent years, marine, freshwater and terrestrial pollution with microplastics has been discussed extensively, whereas atmospheric microplastic transport has been largely overlooked. Here, ...we present global simulations of atmospheric transport of microplastic particles produced by road traffic (TWPs – tire wear particles and BWPs – brake wear particles), a major source that can be quantified relatively well. We find a high transport efficiencies of these particles to remote regions. About 34% of the emitted coarse TWPs and 30% of the emitted coarse BWPs (100 kt yr
−1
and 40 kt yr
−1
respectively) were deposited in the World Ocean. These amounts are of similar magnitude as the total estimated direct and riverine transport of TWPs and fibres to the ocean (64 kt yr
−1
). We suggest that the Arctic may be a particularly sensitive receptor region, where the light-absorbing properties of TWPs and BWPs may also cause accelerated warming and melting of the cryosphere.
The heat wave in late June of 2021 (PNW21) set new temperature records in the Pacific Northwest (PNW). In Lytton the highest temperature ever recorded in Canada was measured. Several studies have ...already explored this extreme event in detail, however, here we compare the atmospheric air mass transport and heating processes associated with this heat wave with the 34 other most extreme heat events in the same region during the period 1960–2021, using a long backtracking time of 25 days. We found significant differences in the heat waves. During PNW21 most of the air was coming from the Philippine Sea, with more than 40% of the air located south of 15°N, and anomalous advection of sensible and latent heat from the Tropics was the dominant cause of PNW21. The latent heat was efficiently converted into sensible heat by precipitation, which was unique, as most other extremes experienced net diabatic cooling.
Plain Language Summary
At the end of June in 2021 a heat wave occurred over the Pacific Northwest (PNW) and led to catastrophic damage in the region, notably the destruction of the town of Lytton by a wild fire 1 day after a new temperature record for Canada was set there. Here we look at where the air during this event was coming from and compare the atmospheric mass transport to 34 other extreme heat events in this region. We found that during the heat wave in June 2021 most of the air was coming from the Philippine Sea where it took up large amounts of heat and moisture. This source region is deeper in the Tropics than for all other extreme events. At the same time, the Philippine Sea was anomalously warm. Thus, the air was warmer and moister than for all the other extreme events already 3 weeks before reaching the PNW. The energy associated with the high tropical moisture content was efficiently converted into heat by precipitation along the Meiyu‐Baiu front—a unique process not found for any other extreme heat event.
Key Points
The air causing the heat wave in late June 2021 (PNW21) came from deep in the Tropics, more south and west compared to other events
Three weeks prior to the event, the air was warmer and moister, indicating that advection of heat from the Tropics was an important driver
Condensation in a warm conveyor belt caused heating for PNW21, while most other extreme events showed overall diabatic cooling
In the Arctic, impurities in the atmosphere and cryosphere can strongly affect the atmospheric radiation and surface energy balance. While black carbon has hence received much attention, mineral dust ...has been in the background. Mineral dust is not only transported into the Arctic from remote regions but also, possibly increasingly, generated in the region itself. Here we study mineral dust in the Arctic based on global transport model simulations. For this, we have developed a dust mobilization scheme in combination with the Lagrangian particle dispersion model FLEXPART. A model evaluation, based on measurements of surface concentrations and annual deposition at a number of stations and aircraft vertical profiles, shows the suitability of this model to study global dust transport. Simulations indicate that about 3% of global dust emission originates from high‐latitude dust sources in the Arctic. Due to limited convection and enhanced efficiency of removal, dust emitted in these source regions is mostly deposited closer to the source than dust from for instance Asia or Africa. This leads to dominant contributions of local dust sources to total surface dust concentrations (~85%) and dust deposition (~90%) in the Arctic region. Dust deposition from local sources peaks in autumn, while dust deposition from remote sources occurs mainly in spring in the Arctic. With increasing altitude, remote sources become more important for dust concentrations as well as deposition. Therefore, total atmospheric dust loads in the Arctic are strongly influenced by Asian (~38%) and African (~32%) dust, whereas local dust contributes only 27%. Dust loads are thus largest in spring when remote dust is efficiently transported into the Arctic. Overall, our study shows that contributions of local dust sources are more important in the Arctic than previously thought, particularly with respect to surface concentrations and dust deposition.
Key Points
High‐latitude dust sources in the Northern Hemisphere contribute substantially to mineral dust in the Arctic and global dust load
Results show a difference between seasonal cycle of dust load and dust deposition in the Arctic
The source region of dust deposited on the Greenland ice sheet changes with altitude
Sea-spray aerosols (SSA) are an important part of the climate system because of their effects on the global radiative budget - both directly as scatterers and absorbers of solar and terrestrial ...radiation, and indirectly as cloud condensation nuclei (CCN) influencing cloud formation, lifetime, and precipitation. In terms of their global mass, SSA have the largest uncertainty of all aerosols. In this study we review 21 SSA source functions from the literature, several of which are used in current climate models. In addition, we propose a~new function. Even excluding outliers, the global annual SSA mass produced spans roughly 3-70 Pg yr-1 for the different source functions, for particles with dry diameter Dp < 10 mu m, with relatively little interannual variability for a given function. The FLEXPART Lagrangian particle dispersion model was run in backward mode for a large global set of observed SSA concentrations, comprised of several station networks and ship cruise measurement campaigns. FLEXPART backward calculations produce gridded emission sensitivity fields, which can subsequently be multiplied with gridded SSA production fluxes in order to obtain modeled SSA concentrations. This allowed us to efficiently and simultaneously evaluate all 21 source functions against the measurements. Another advantage of this method is that source-region information on wind speed and sea surface temperatures (SSTs) could be stored and used for improving the SSA source function parameterizations. The best source functions reproduced as much as 70% of the observed SSA concentration variability at several stations, which is comparable with "state of the art" aerosol models. The main driver of SSA production is wind, and we found that the best fit to the observation data could be obtained when the SSA production is proportional to U103.5, where U10 is the source region averaged 10 m wind speed. A strong influence of SST on SSA production, with higher temperatures leading to higher production, could be detected as well, although the underlying physical mechanisms of the SST influence remains unclear. Our new source function with wind speed and temperature dependence gives a global SSA production for particles smaller than Dp < 10 mu m of 9 Pg yr-1, and is the best fit to the observed concentrations.
On 11 March 2011, an earthquake occurred about 130 km off the Pacific coast of Japan's main island Honshu, followed by a large tsunami. The resulting loss of electric power at the Fukushima Dai-ichi ...nuclear power plant developed into a disaster causing massive release of radioactivity into the atmosphere. In this study, we determine the emissions into the atmosphere of two isotopes, the noble gas xenon-133 (133Xe) and the aerosol-bound caesium-137 (137Cs), which have very different release characteristics as well as behavior in the atmosphere. To determine radionuclide emissions as a function of height and time until 20 April, we made a first guess of release rates based on fuel inventories and documented accident events at the site. This first guess was subsequently improved by inverse modeling, which combined it with the results of an atmospheric transport model, FLEXPART, and measurement data from several dozen stations in Japan, North America and other regions. We used both atmospheric activity concentration measurements as well as, for 137Cs, measurements of bulk deposition. Regarding 133Xe, we find a total release of 15.3 (uncertainty range 12.2–18.3) EBq, which is more than twice as high as the total release from Chernobyl and likely the largest radioactive noble gas release in history. The entire noble gas inventory of reactor units 1–3 was set free into the atmosphere between 11 and 15 March 2011. In fact, our release estimate is higher than the entire estimated 133Xe inventory of the Fukushima Dai-ichi nuclear power plant, which we explain with the decay of iodine-133 (half-life of 20.8 h) into 133Xe. There is strong evidence that the 133Xe release started before the first active venting was made, possibly indicating structural damage to reactor components and/or leaks due to overpressure which would have allowed early release of noble gases. For 137Cs, the inversion results give a total emission of 36.6 (20.1–53.1) PBq, or about 43% of the estimated Chernobyl emission. Our results indicate that 137Cs emissions peaked on 14–15 March but were generally high from 12 until 19 March, when they suddenly dropped by orders of magnitude at the time when spraying of water on the spent-fuel pool of unit 4 started. This indicates that emissions may not have originated only from the damaged reactor cores, but also from the spent-fuel pool of unit 4. This would also confirm that the spraying was an effective countermeasure. We explore the main dispersion and deposition patterns of the radioactive cloud, both regionally for Japan as well as for the entire Northern Hemisphere. While at first sight it seemed fortunate that westerly winds prevailed most of the time during the accident, a different picture emerges from our detailed analysis. Exactly during and following the period of the strongest 137Cs emissions on 14 and 15 March as well as after another period with strong emissions on 19 March, the radioactive plume was advected over Eastern Honshu Island, where precipitation deposited a large fraction of 137Cs on land surfaces. Radioactive clouds reached North America on 15 March and Europe on 22 March. By middle of April, 133Xe was fairly uniformly distributed in the middle latitudes of the entire Northern Hemisphere and was for the first time also measured in the Southern Hemisphere (Darwin station, Australia). In general, simulated and observed concentrations of 133Xe and 137Cs both at Japanese as well as at remote sites were in good quantitative agreement. Altogether, we estimate that 6.4 PBq of 137Cs, or 18% of the total fallout until 20 April, were deposited over Japanese land areas, while most of the rest fell over the North Pacific Ocean. Only 0.7 PBq, or 1.9% of the total fallout were deposited on land areas other than Japan.
Arctic haze is a seasonal phenomenon with high concentrations of accumulation-mode aerosols occurring in the Arctic in winter and early spring. Chemistry transport models and climate chemistry models ...struggle to reproduce this phenomenon, and this has recently prompted changes in aerosol removal schemes to remedy the modeling problems. In this paper, we show that shortcomings in current emission data sets are at least as important. We perform a 3 yr model simulation of black carbon (BC) with the Lagrangian particle dispersion model FLEXPART. The model is driven with a new emission data set ("ECLIPSE emissions") which includes emissions from gas flaring. While gas flaring is estimated to contribute less than 3% of global BC emissions in this data set, flaring dominates the estimated BC emissions in the Arctic (north of 66° N). Putting these emissions into our model, we find that flaring contributes 42% to the annual mean BC surface concentrations in the Arctic. In March, flaring even accounts for 52% of all Arctic BC near the surface. Most of the flaring BC remains close to the surface in the Arctic, so that the flaring contribution to BC in the middle and upper troposphere is small. Another important factor determining simulated BC concentrations is the seasonal variation of BC emissions from residential combustion (often also called domestic combustion, which is used synonymously in this paper). We have calculated daily residential combustion emissions using the heating degree day (HDD) concept based on ambient air temperature and compare results from model simulations using emissions with daily, monthly and annual time resolution. In January, the Arctic-mean surface concentrations of BC due to residential combustion emissions are 150% higher when using daily emissions than when using annually constant emissions. While there are concentration reductions in summer, they are smaller than the winter increases, leading to a systematic increase of annual mean Arctic BC surface concentrations due to residential combustion by 68% when using daily emissions. A large part (93%) of this systematic increase can be captured also when using monthly emissions; the increase is compensated by a decreased BC burden at lower latitudes. In a comparison with BC measurements at six Arctic stations, we find that using daily-varying residential combustion emissions and introducing gas flaring emissions leads to large improvements of the simulated Arctic BC, both in terms of mean concentration levels and simulated seasonality. Case studies based on BC and carbon monoxide (CO) measurements from the Zeppelin observatory appear to confirm flaring as an important BC source that can produce pollution plumes in the Arctic with a high BC / CO enhancement ratio, as expected for this source type. BC measurements taken during a research ship cruise in the White, Barents and Kara seas north of the region with strong flaring emissions reveal very high concentrations of the order of 200–400 ng m−3. The model underestimates these concentrations substantially, which indicates that the flaring emissions (and probably also other emissions in northern Siberia) are rather under- than overestimated in our emission data set. Our results suggest that it may not be "vertical transport that is too strong or scavenging rates that are too low" and "opposite biases in these processes" in the Arctic and elsewhere in current aerosol models, as suggested in a recent review article (Bond et al., Bounding the role of black carbon in the climate system: a scientific assessment, J. Geophys. Res., 2013), but missing emission sources and lacking time resolution of the emission data that are causing opposite model biases in simulated BC concentrations in the Arctic and in the mid-latitudes.
The intensity of the heaviest extreme precipitation events is known to increase with global warming. How often such events occur in a warmer world is however less well established, and the combined ...effect of changes in frequency and intensity on the total amount of rain falling as extreme precipitation is much less explored, in spite of potentially large societal impacts. Here, we employ observations and climate model simulations to document strong increases in the frequencies of extreme precipitation events occurring on decadal timescales. Based on observations we find that the total precipitation from these intense events almost doubles per degree of warming, mainly due to changes in frequency, while the intensity changes are relatively weak, in accordance to previous studies. This shift towards stronger total precipitation from extreme events is seen in observations and climate models, and increases with the strength - and hence the rareness - of the event. Based on these results, we project that if historical trends continue, the most intense precipitation events observed today are likely to almost double in occurrence for each degree of further global warming. Changes to extreme precipitation of this magnitude are dramatically stronger than the more widely communicated changes to global mean precipitation.
In September 2005, an extreme precipitation event occurred on the Norwegian southwest coast, which produced flooding and landslides and caused considerable infrastructure damage and loss of human ...life. We found that this event was triggered by the transport of tropical and subtropical moisture associated with two former hurricanes, Maria and Nate, which both underwent transition into extratropical cyclones. The two former hurricanes generated a large stream of (sub)tropical air which extended over more than 40° of latitude and across the North Atlantic Ocean and carried a large amount of moisture originally associated with hurricane Nate; a so‐called atmospheric river or moisture conveyor belt. The mountains along the Norwegian coast caused a strong orographic enhancement of the precipitation associated with the moist air. A Lagrangian moisture tracking algorithm was employed to show that the evaporative source of the precipitation falling over Norway was distributed over large parts of the North Atlantic Ocean, and indeed included large contribution from the subtropics and smaller ones from the tropics. The moisture tracking algorithm was also applied over a 5‐year period. It was found that (sub)tropical sources can contribute substantially to the precipitation falling in southwestern Norway throughout the year. Thus other transport mechanisms than hurricanes are important, too, for moving (sub)tropical moisture so far north. The (sub)tropical moisture source is relatively more important during the positive phase of the North Atlantic Oscillation, as well as for stronger precipitation events.
Mineral dust sources at high and low latitudes contribute to atmospheric dust loads and dust deposition in the Arctic. With dust load estimates from Groot Zwaaftink et al. (, ...https://doi.org/10.1002/2016JD025482), we quantify the mineral dust instantaneous radiative forcing (IRF) in the Arctic for the year 2012. The annual‐mean top of the atmosphere IRF is 0.225 W/m2, with the largest contributions from dust transported from Asia south of 60°N and Africa. High‐latitude (>60°N) dust sources contribute about 39% to top of the atmosphere IRF and have a larger impact (1 to 2 orders of magnitude) on IRF per emitted kilogram of dust than low‐latitude sources. Mineral dust deposited on snow accounts for nearly all of the bottom of the atmosphere IRF of 0.135 W/m2. More than half of the bottom of the atmosphere IRF is caused by dust from high‐latitude sources, indicating substantial regional climate impacts rarely accounted for in current climate models.
Plain Language Summary
Mineral dust sources at high and low latitudes contribute to atmospheric dust loads and dust deposition in the Arctic. We quantify the annual‐mean radiative forcing (RF) in the Arctic to be 0.225 W/m2 at the top of the atmosphere. The largest contributions are from dust transported from Asia south of 60°N and Africa. High‐latitude (>60°N) dust sources contribute about 39% to top of the atmosphere RF and have a larger (1 to 2 orders of magnitude) impact on RF per emitted kilogram of dust. Mineral dust deposited on snow accounts for nearly all of the bottom of the atmosphere RF of 0.135 W/m2. More than half of the bottom of the atmosphere RF is caused by dust from high‐latitude sources, indicating substantial regional climate impacts rarely accounted for in current climate models.
Key Points
Arctic top of the atmosphere mineral dust radiative forcing (RF) is dominated by dust from Asia and Africa
Deposited dust accounts for half of the top of the atmosphere RF and nearly all of the bottom of the atmosphere RF
Most of the dust deposited and thus most of the bottom of the atmosphere RF is contributed by high‐latitude dust sources
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