The South Asian monsoon-pollution pump and purifier Lelieveld, J; Bourtsoukidis, E; Brühl, C ...
Science (American Association for the Advancement of Science),
2018-Jul-20, 2018-07-20, 20180720, Letnik:
361, Številka:
6399
Journal Article
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Air pollution is growing fastest in monsoon-affected South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the ...wet summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism by which contaminants are rapidly oxidized and deposited to Earth's surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.
Measurements made by the MOPITT (“Measurements of Pollution in the Troposphere”) instrument on the NASA Terra polar-orbiting platform enable the retrieval of tropospheric carbon monoxide (CO) ...concentrations. As determined by the Terra orbit and MOPITT swath width, the frequency of MOPITT observations at a specific location, or measurement sampling frequency, is typically about once every three to four days. However, because the MOPITT retrieval algorithm is only applicable to clear-sky scenes, MOPITT retrieval sampling frequency strongly depends on regional cloudiness and can be much smaller than the measurement sampling frequency. Moreover, highly polluted scenes, characterized by high aerosol optical depths, can be confused with cloudy scenes and thus be discarded unnecessarily by the MOPITT cloud detection algorithm. Herein are described revisions to this algorithm which substantially increase retrieval sampling over land in varying pollution conditions. The performance of the revised cloud detection algorithm is evaluated through validation, case studies, and continental-scale maps of retrieval sampling frequency. Presented case studies illustrate (1) why the current operational MOPITT cloud detection algorithm excludes extended areas of potentially valuable cloud-free MOPITT observations and (2) how, for the same scenes, improved retrieval coverage benefits analyses of regional CO variability. Maps of retrieval sampling frequency for South America and Asia exhibit well-defined improvements, especially in regions with poor sampling frequency in the current product.
•The current MOPITT cloud detection algorithm is often overly conservative.•Algorithm revisions resulting in improved sampling are described and evaluated.•Case studies illustrate improved retrieval coverage in both clean and polluted scenes.
To mitigate the diesel particle pollution problem, diesel vehicles are fitted with modern exhaust after-treatment systems (ATS), which efficiently remove engine-generated primary particles (soot and ...ash) and gaseous hydrocarbons. Unfortunately, ATS can promote formation of low-vapor-pressure gases, which may undergo nucleation and condensation leading to formation of nucleation particles (NUP). The chemical nature and formation mechanism of these particles are only poorly explored. Using a novel mass spectrometric method, online measurements of low-vapor-pressure gases were performed for exhaust of a modern heavy-duty diesel engine operated with modern ATS and combusting low and ultralow sulfur fuels and also biofuel. It was observed that the gaseous sulfuric acid (GSA) concentration varied strongly, although engine operation was stable. However, the exhaust GSA was observed to be affected by fuel sulfur level, exhaust after-treatment, and driving conditions. Significant GSA concentrations were measured also when biofuel was used, indicating that GSA can be originated also from lubricant oil sulfur. Furthermore, accompanying NUP measurements and NUP model simulations were performed. We found that the exhaust GSA promotes NUP formation, but also organic (acidic) precursor gases can have a role. The model results indicate that that the measured GSA concentration alone is not high enough to grow the particles to the detected sizes.
We describe results of in situ observations of a 1‐ to 2‐min‐old contrail in the vortex phase generated from soot‐rich exhaust (>1015 emitted soot particles per kilogram of fuel burned). Simultaneous ...measurements of soot (EIsoot) and apparent ice (AEIice) particle number emission indices show a pronounced anticorrelation in the vertical contrail profile. AEIice decrease by about 75% with increasing distance below the contrail‐producing aircraft, while EIsoot increase by an equivalent relative fraction, therefore strongly suggesting ice particle formation to be soot‐controlled and losses to be caused by sublimation. Quantifying these losses in measurements helps to validate and improve contrail parameterizations used to estimate the climate impact of contrails and contrail cirrus. Our study further demonstrates the challenges in the performance and interpretation of particle measurements in young contrails and lends itself to suggestions for improving contrail data evaluation.
Plain Language Summary
Detailed understanding of climatic effects of aircraft contrails and the clouds evolving from them requires accurate in situ measurements. We took measurements in a young persistent contrail that formed at 10 km altitude. We found that a substantial fraction of contrail ice particles is lost shortly after they formed from emissions of copious soot particles from aircraft jet engines. While these results are not entirely unexpected and can be explained by sublimation associated with adiabatic heating in descending aircraft wake vortices, experimental verification is challenging. Importantly, our results increase confidence in the current understanding of processes governing contrail ice formation, growth, and sublimation during early development stages. We provide guidance on quantifying ice particle number concentrations in young contrails and how to relate them to particle emissions. We expect our results to be also beneficial to future studies addressing properties and climate impact of contrails originating from using alternative jet fuels or novel engine technologies.
Key Points
Results of aircraft measurements of microphysical properties in a young, soot-rich contrail are presented
We found a pronounced reduction of ice particle numbers in lower wake regions
Vertical profiles of soot and ice particle numbers are consistent with soot-controlled ice formation
The investigation of the impact of aircraft parameters on contrail properties helps to better understand the climate impact from aviation. Yet, in observations, it is a challenge to separate aircraft ...and meteorological influences on contrail formation. During the CONCERT campaign in November 2008, contrails from 3 Airbus passenger aircraft of types A319-111, A340-311 and A380-841 were probed at cruise under similar meteorological conditions with in situ instruments on board DLR research aircraft Falcon. Within the 2 min-old contrails detected near ice saturation, we find similar effective diameters Deff (5.2–5.9 μm), but differences in particle number densities nice (162–235 cm−3) and in vertical contrail extensions (120–290 m), resulting in large differences in contrail optical depths τ at 550 nm (0.25–0.94). Hence larger aircraft produce optically thicker contrails. Based on the observations, we apply the EULAG-LCM model with explicit ice microphysics and, in addition, the Contrail and Cirrus Prediction (CoCiP) model to calculate the aircraft type impact on young contrails under identical meteorological conditions. The observed increase in τ for heavier aircraft is confirmed by the models, yet for generally smaller τ. CoCiP model results suggest that the aircraft dependence of climate-relevant contrail properties persists during contrail lifetime, adding importance to aircraft-dependent model initialization. We finally derive an analytical relationship between contrail, aircraft and meteorological parameters. Near ice saturation, contrail width × τ scales linearly with the fuel flow rate, as confirmed by observations. For higher relative humidity with respect to ice (RHI), the analytical relationship suggests a non-linear increase in the form (RHI-12/3. Summarized, our combined results could help to more accurately assess the climate impact from aviation using an aircraft-dependent contrail parameterization.
The eruption of the Eyjafjallajökull volcano, Iceland, in April and May 2010 caused unprecedented disruptions of European air traffic showing that timely monitoring of volcanic ash and SO2 dispersion ...as well as the corresponding plume heights are important for aviation safety. This paper describes the observations of SO2 and BrO columns in the eruption plume and the determination of the SO2 plume height using the GOME‐2 satellite instrument. During the eruptive period in May 2010, SO2 total columns of up to ∼20 DU and BrO columns of ∼7.7 × 1013 molec/cm2 were detected. The BrO/SO2 ratio estimated from the GOME‐2 observations of the Eyjafjallajökull eruption varies from 1.1 × 10−4 to 2.1 × 10−4. The SO2 plume heights estimated from the GOME‐2 observations on 5 May range from 8–13 km and mostly agree within 1–3 km with visual observations, radar data and modeling results. Furthermore, the GOME‐2 SO2 observations are compared with in situ measurements of the DLR Falcon aircraft on 17 and 18 May 2010 and with Brewer instruments at Valentia, Ireland and Hohenpeissenberg, Germany. The SO2 columns derived from the Falcon profile measurements range from 0.6–4.7 DU and the comparison with the GOME‐2 measurements shows a good agreement, mainly within 1 DU. The Brewer observations at Hohenpeissenberg also agree well with the GOME‐2 measurements with a daily average SO2 column of ∼1.3 DU during the overpass of the SO2 cloud on 18 May, whereas the Brewer instrument at Valentia shows up to 50% higher SO2 columns (∼8 DU) on 11 May.
Key Points
SO2 and BrO in the eruption plume of Eyjafjallajokull using GOME‐2
Direct retreival of the SO2 plume height from GOME‐2 measurements
Comparison of GOME‐2 data with model simulations, Falcon and Brewer observations
This study investigates the evolution of ship-emitted aerosol particles using the stochastic particle-resolved model PartMC-MOSAIC (Particle Monte Carlo model-Model for Simulating Aerosol ...Interactions and Chemistry). Comparisons of our results with observations from the QUANTIFY (Quantifying the Climate Impact of Global and European Transport Systems) study in 2007 in the English Channel and the Gulf of Biscay showed that the model was able to reproduce the observed evolution of total number concentration and the vanishing of the nucleation mode consisting of sulfate particles. Further process analysis revealed that during the first hour after emission, dilution reduced the total number concentration by four orders of magnitude, while coagulation reduced it by an additional order of magnitude. Neglecting coagulation resulted in an overprediction of more than one order of magnitude in the number concentration of particles smaller than 40 nm at a plume age of 100 s. Coagulation also significantly altered the mixing state of the particles, leading to a continuum of internal mixtures of sulfate and black carbon. The impact on cloud condensation nuclei (CCN) concentrations depended on the supersaturation threshold S at which CCN activity was evaluated. For the base case conditions, characterized by a low formation rate of secondary aerosol species, neglecting coagulation, but simulating condensation, led to an underestimation of CCN concentrations of about 37% for S = 0.3% at the end of the 14-h simulation. In contrast, for supersaturations higher than 0.7%, neglecting coagulation resulted in an overestimation of CCN concentration, about 75% for S = 1%. For S lower than 0.2% the differences between simulations including coagulation and neglecting coagulation were negligible. Neglecting condensation, but simulating coagulation did not impact the CCN concentrations below 0.2% and resulted in an underestimation of CCN concentrations for larger supersaturations, e.g., 18% for S = 0.6%. We also explored the role of nucleation for the CCN concentrations in the ship plume. For the base case the impact of nucleation on CCN concentrations was limited, but for a sensitivity case with higher formation rates of secondary aerosol over several hours, the CCN concentrations increased by an order of magnitude for supersaturation thresholds above 0.3%.
Vertically resolved distributions of sulfur dioxide (SO2) with global coverage in the height region from the upper troposphere to ~20 km altitude have been derived from observations by the Michelson ...Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat for the period July 2002 to April 2012. Retrieved volume mixing ratio profiles representing single measurements are characterized by typical errors in the range of 70-100 pptv and by a vertical resolution ranging from 3 to 5 km. Comparison with observations by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) revealed a slightly varying bias with altitude of -20 to 50 pptv for the MIPAS data set in case of volcanically enhanced concentrations. For background concentrations the comparison showed a systematic difference between the two major MIPAS observation periods. After debiasing, the difference could be reduced to biases within -10 to 20 pptv in the altitude range of 10-20 km with respect to ACE-FTS. Further comparisons of the debiased MIPAS data set with in situ measurements from various aircraft campaigns showed no obvious inconsistencies within a range of around plus or minus 50 pptv. The SO2 emissions of more than 30 volcanic eruptions could be identified in the upper troposphere and lower stratosphere (UTLS). Emitted SO2 masses and lifetimes within different altitude ranges in the UTLS have been derived for a large part of these eruptions. Masses are in most cases within estimations derived from other instruments. From three of the major eruptions within the MIPAS measurement period - Kasatochi in August 2008, Sarychev in June 2009 and Nabro in June 2011 - derived lifetimes of SO2 for the altitude ranges 10-14, 14-18 and 18-22 km are 13.3 plus or minus 2.1, 23.6 plus or minus 1.2 and 32.3 plus or minus 5.5 days respectively. By omitting periods with obvious volcanic influence we have derived background mixing ratio distributions of SO2. At 10 km altitude these indicate an annual cycle at northern mid- and high latitudes with maximum values in summer and an amplitude of about 30 pptv. At higher altitudes of about 16-18 km, enhanced mixing ratios of SO2 can be found in the regions of the Asian and the North American monsoons in summer - a possible connection to an aerosol layer discovered by Vernier et al. (2011b) in that region.
A case of long‐range transport of a biomass burning plume from Alaska to Europe is analyzed using a Lagrangian approach. This plume was sampled several times in the free troposphere over North ...America, the North Atlantic and Europe by three different aircraft during the IGAC Lagrangian 2K4 experiment which was part of the ICARTT/ITOP measurement intensive in summer 2004. Measurements in the plume showed enhanced values of CO, VOCs and NOy, mainly in form of PAN. Observed O3 levels increased by 17 ppbv over 5 days. A photochemical trajectory model, CiTTyCAT, was used to examine processes responsible for the chemical evolution of the plume. The model was initialized with upwind data and compared with downwind measurements. The influence of high aerosol loading on photolysis rates in the plume was investigated using in situ aerosol measurements in the plume and lidar retrievals of optical depth as input into a photolysis code (Fast‐J), run in the model. Significant impacts on photochemistry are found with a decrease of 18% in O3 production and 24% in O3 destruction over 5 days when including aerosols. The plume is found to be chemically active with large O3 increases attributed primarily to PAN decomposition during descent of the plume toward Europe. The predicted O3 changes are very dependent on temperature changes during transport and also on water vapor levels in the lower troposphere which can lead to O3 destruction. Simulation of mixing/dilution was necessary to reproduce observed pollutant levels in the plume. Mixing was simulated using background concentrations from measurements in air masses in close proximity to the plume, and mixing timescales (averaging 6.25 days) were derived from CO changes. Observed and simulated O3/CO correlations in the plume were also compared in order to evaluate the photochemistry in the model. Observed slopes change from negative to positive over 5 days. This change, which can be attributed largely to photochemistry, is well reproduced by multiple model runs even if slope values are slightly underestimated suggesting a small underestimation in modeled photochemical O3 production. The possible impact of this biomass burning plume on O3 levels in the European boundary layer was also examined by running the model for a further 5 days and comparing with data collected at surface sites, such as Jungfraujoch, which showed small O3 increases and elevated CO levels. The model predicts significant changes in O3 over the entire 10 day period due to photochemistry but the signal is largely lost because of the effects of dilution. However, measurements in several other BB plumes over Europe show that O3 impact of Alaskan fires can be potentially significant over Europe.
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