Many cities in the world experience significant air pollution from residential wood combustion. S... more Many cities in the world experience significant air pollution from residential wood combustion. Such an advection–diffusion problem as applied to geographically distributed small-scale pollution sources presently does not have a satisfactory theoretical or modeling solution. For ex- ample, statistical models do not allow for pollution accumu- lation in local stagnation zones – a type of phenomena that is commonly observed over complex terrain. This study applies a Parallelized Atmospheric Large-eddy simulation Model (PALM) to investigate dynamical phenomena that control variability and pathways of the atmospheric pollution emitted by wood-burning household stoves. The model PALM runs at spatial resolution of 10m in an urban-sized modeling domain of 29km by 35km with a real spatial distribution of the pol- lution source and with realistic surface boundary conditions that characterize a medium-sized urban area fragmented by water bodies and hills. Such complex geography is expected to favor local air quality hazards, which makes this study of general interest. The case study here is based on winter con- ditions in Bergen, Norway. We investigate the turbulent diffu- sion of a passive scalar associated with small-sized particles (PM2.5) emitted by household stoves. The study considers air pollution effects that could be observed under different pol- icy scenarios of stove replacement; modern woodstoves emit significantly less PM2.5 than the older ones, but replacement of stoves is a costly and challenging process. We found significant accumulation of near-surface pollu- tion in the local stagnation zones. The simulated concentra- tions were larger than the concentrations obtained only due to the local PM2.5 emission, thus indicating dominant trans- boundary contribution of pollutants for other districts. We demonstrate how the source of critical pollution can be at- tributed through model disaggregation of emission from spe- cific districts. The study reveals a decisive role of local air circulations over complex terrain that makes high-resolution modeling indispensable for adequate management of the ur- ban air quality. This modeling study has important policy-related implica- tions. Uneven spatial distribution of the pollutants suggests prioritizing certain limited urban districts in policy scenarios. We show that focused efforts towards stove replacement in specific areas may have a dominant positive effect on the air quality in the whole municipality. The case study identifies urban districts where limited incentives would result in the strongest reduction of the population’s exposure to PM2.5.
This paper considers a possibility to combine computational fluid dynamics and statistical artifi... more This paper considers a possibility to combine computational fluid dynamics and statistical artificial neural network (ANN) approaches to deal with complex surface features of urban environment in large-eddy simulations (LES). At this stage, only a priori analysis is applied for idealized, relatively coarse resolution numerical experiments. It is shown that the filtering property of the three layers' ANN can be
Surface atmospheric temperature (SAT) measurements are the most reliable atmospheric temperature ... more Surface atmospheric temperature (SAT) measurements are the most reliable atmospheric temperature data characterizing the temperature at standard meteorological height 2 m. However, contrary to what has been implicitly assumed in the Climate Change debates, changes in the SAT often have loose relations with changes in the atmospheric heat content. These relations depend on regimes of turbulent mixing within the planetary boundary layer (PBL). The only source of turbulent energy in the wintertime Arctic - the wind shear - strongly depends on storm activity. Strong atmospheric temperature inversions (ATI) typical in the Arctic inhibit the mixing between a thin PBL and the adjacent troposphere. Physical reasoning suggests that a thin gas layer would quickly equilibrate its temperature with the boundaries. Capped by a very strong ATI, the SAT equilibrates with the surface temperature, which is typically of 10K (potentially) colder than the lower troposphere. A weak ATI in a storm-mixed troposphere permits the turbulence to penetrate deeper into the troposphere and to rise the SAT. Observations (e.g. SHEBA campaign) revealed that these two mixing regimes produce a bi-modal distribution in the SAT. The coldest temperature maximum in the distribution does not find its counterpart in the tropospheric temperatures. The mixing regimes in the Arctic PBL may have profound impact on the Arctic climate and climate change. Firstly, the observed SAT trends should be the combination of the trends due to changes in the atmospheric heat content and due to changes in the frequency of the mixing regimes. The latter changes reflect rather changes in storm activity than changes in a local heat budget. Using ERA-40 data, the impact of PBL regimes on the Arctic warming is quantified. Up to 70% of the SAT trends over the Atlantic could be attributed to changes in the PBL mixing. These changes account up to 50% of the SAT trends over East Europe, East Arctic and Alaska. Secondly, the warming tropospheric trends should result in ATI strengthening leading to a weaker warming or even cooling traced in the SAT. Only small changes in the PBL mixing have been found over Siberia and Canada. Strong warming trends in those areas in 70s - 80s has changed to small or negative trends in the recent years. Partially, it could be due to the PBL response on warmer troposphere and stronger temperature inversions. As any transitional process in a thin layer, this SAT trend inconsistency will be limited both in time and amplitude. Turbulence resolving simulations of responses in the Arctic PBL suggest that amplitude of the local changes could reach 10K, which means that global processes would need additional one-two decades to overcome the PBL changes. One should also expect temporal lingering of the SAT increase in central areas of continents.
This study presents results from the specific large-eddy simulation study of the urban boundary l... more This study presents results from the specific large-eddy simulation study of the urban boundary layer in the MEGAPOLI Paris Plume field campaign. We used LESNIC and PALM codes, MEGAPOLI city morphology database, nudging to the observed meteorological conditions during the Paris Plume campaign and some concentration measurements from that campaign to simulate and better understand the nature of the urban
The Coriolis force is recognized as the major control factor in the shear-driven non-stratified t... more The Coriolis force is recognized as the major control factor in the shear-driven non-stratified turbulent boundary layer since the work of F. Nansen and V. Ekman in 1898. However, in geophysics (meteorology and oceanography), the central attention is paid to the vertical component of the force whereas the horizontal component is generally omitted. Contrary, in turbo-machinery, effects of the latter
ABSTRACT Atmospheric conditions observed during the cold winter 2010-2011 in Bergen resulted in a... more ABSTRACT Atmospheric conditions observed during the cold winter 2010-2011 in Bergen resulted in a case of extreme air quality hazard. Very high concentrations of the atmospheric pollutants, notably NO2, were measured. Attempts to reduce their emission rates by policy measures leaded to city life disorganization and severe economic damage. Using the advantage of turbulence-resolving simulations and extensive meteorological observations in the city, analysis of the event has been conducted. The simulations (the mesh resolution was 30 m) combined with the available emission inventory recovered the detailed map of the concentrations. It has been demonstrated that the slope winds contributed considerably into the air quality hazard. Moreover, it was shown that only a special type of temperature inversion in the central Bergen area contributes to this event. The strong clear sky radiation cooling in Bergen causes cold air subsidence along the hill slopes and the near surface northward flow. At the same time the mean air flow is directed southward as atmospheric soundings reveal. Above the central city area those flows meet and lock polluted air. The strong radiative inversion, seen both in the model and in the data from Geophysical Institute, prevent normal air mixing in the deep layer. The inversion top is clearly seen on the photo as the height of improved visibility.
Many cities in the world experience significant air pollution from residential wood combustion. S... more Many cities in the world experience significant air pollution from residential wood combustion. Such an advection–diffusion problem as applied to geographically distributed small-scale pollution sources presently does not have a satisfactory theoretical or modeling solution. For ex- ample, statistical models do not allow for pollution accumu- lation in local stagnation zones – a type of phenomena that is commonly observed over complex terrain. This study applies a Parallelized Atmospheric Large-eddy simulation Model (PALM) to investigate dynamical phenomena that control variability and pathways of the atmospheric pollution emitted by wood-burning household stoves. The model PALM runs at spatial resolution of 10m in an urban-sized modeling domain of 29km by 35km with a real spatial distribution of the pol- lution source and with realistic surface boundary conditions that characterize a medium-sized urban area fragmented by water bodies and hills. Such complex geography is expected to favor local air quality hazards, which makes this study of general interest. The case study here is based on winter con- ditions in Bergen, Norway. We investigate the turbulent diffu- sion of a passive scalar associated with small-sized particles (PM2.5) emitted by household stoves. The study considers air pollution effects that could be observed under different pol- icy scenarios of stove replacement; modern woodstoves emit significantly less PM2.5 than the older ones, but replacement of stoves is a costly and challenging process. We found significant accumulation of near-surface pollu- tion in the local stagnation zones. The simulated concentra- tions were larger than the concentrations obtained only due to the local PM2.5 emission, thus indicating dominant trans- boundary contribution of pollutants for other districts. We demonstrate how the source of critical pollution can be at- tributed through model disaggregation of emission from spe- cific districts. The study reveals a decisive role of local air circulations over complex terrain that makes high-resolution modeling indispensable for adequate management of the ur- ban air quality. This modeling study has important policy-related implica- tions. Uneven spatial distribution of the pollutants suggests prioritizing certain limited urban districts in policy scenarios. We show that focused efforts towards stove replacement in specific areas may have a dominant positive effect on the air quality in the whole municipality. The case study identifies urban districts where limited incentives would result in the strongest reduction of the population’s exposure to PM2.5.
This paper considers a possibility to combine computational fluid dynamics and statistical artifi... more This paper considers a possibility to combine computational fluid dynamics and statistical artificial neural network (ANN) approaches to deal with complex surface features of urban environment in large-eddy simulations (LES). At this stage, only a priori analysis is applied for idealized, relatively coarse resolution numerical experiments. It is shown that the filtering property of the three layers' ANN can be
Surface atmospheric temperature (SAT) measurements are the most reliable atmospheric temperature ... more Surface atmospheric temperature (SAT) measurements are the most reliable atmospheric temperature data characterizing the temperature at standard meteorological height 2 m. However, contrary to what has been implicitly assumed in the Climate Change debates, changes in the SAT often have loose relations with changes in the atmospheric heat content. These relations depend on regimes of turbulent mixing within the planetary boundary layer (PBL). The only source of turbulent energy in the wintertime Arctic - the wind shear - strongly depends on storm activity. Strong atmospheric temperature inversions (ATI) typical in the Arctic inhibit the mixing between a thin PBL and the adjacent troposphere. Physical reasoning suggests that a thin gas layer would quickly equilibrate its temperature with the boundaries. Capped by a very strong ATI, the SAT equilibrates with the surface temperature, which is typically of 10K (potentially) colder than the lower troposphere. A weak ATI in a storm-mixed troposphere permits the turbulence to penetrate deeper into the troposphere and to rise the SAT. Observations (e.g. SHEBA campaign) revealed that these two mixing regimes produce a bi-modal distribution in the SAT. The coldest temperature maximum in the distribution does not find its counterpart in the tropospheric temperatures. The mixing regimes in the Arctic PBL may have profound impact on the Arctic climate and climate change. Firstly, the observed SAT trends should be the combination of the trends due to changes in the atmospheric heat content and due to changes in the frequency of the mixing regimes. The latter changes reflect rather changes in storm activity than changes in a local heat budget. Using ERA-40 data, the impact of PBL regimes on the Arctic warming is quantified. Up to 70% of the SAT trends over the Atlantic could be attributed to changes in the PBL mixing. These changes account up to 50% of the SAT trends over East Europe, East Arctic and Alaska. Secondly, the warming tropospheric trends should result in ATI strengthening leading to a weaker warming or even cooling traced in the SAT. Only small changes in the PBL mixing have been found over Siberia and Canada. Strong warming trends in those areas in 70s - 80s has changed to small or negative trends in the recent years. Partially, it could be due to the PBL response on warmer troposphere and stronger temperature inversions. As any transitional process in a thin layer, this SAT trend inconsistency will be limited both in time and amplitude. Turbulence resolving simulations of responses in the Arctic PBL suggest that amplitude of the local changes could reach 10K, which means that global processes would need additional one-two decades to overcome the PBL changes. One should also expect temporal lingering of the SAT increase in central areas of continents.
This study presents results from the specific large-eddy simulation study of the urban boundary l... more This study presents results from the specific large-eddy simulation study of the urban boundary layer in the MEGAPOLI Paris Plume field campaign. We used LESNIC and PALM codes, MEGAPOLI city morphology database, nudging to the observed meteorological conditions during the Paris Plume campaign and some concentration measurements from that campaign to simulate and better understand the nature of the urban
The Coriolis force is recognized as the major control factor in the shear-driven non-stratified t... more The Coriolis force is recognized as the major control factor in the shear-driven non-stratified turbulent boundary layer since the work of F. Nansen and V. Ekman in 1898. However, in geophysics (meteorology and oceanography), the central attention is paid to the vertical component of the force whereas the horizontal component is generally omitted. Contrary, in turbo-machinery, effects of the latter
ABSTRACT Atmospheric conditions observed during the cold winter 2010-2011 in Bergen resulted in a... more ABSTRACT Atmospheric conditions observed during the cold winter 2010-2011 in Bergen resulted in a case of extreme air quality hazard. Very high concentrations of the atmospheric pollutants, notably NO2, were measured. Attempts to reduce their emission rates by policy measures leaded to city life disorganization and severe economic damage. Using the advantage of turbulence-resolving simulations and extensive meteorological observations in the city, analysis of the event has been conducted. The simulations (the mesh resolution was 30 m) combined with the available emission inventory recovered the detailed map of the concentrations. It has been demonstrated that the slope winds contributed considerably into the air quality hazard. Moreover, it was shown that only a special type of temperature inversion in the central Bergen area contributes to this event. The strong clear sky radiation cooling in Bergen causes cold air subsidence along the hill slopes and the near surface northward flow. At the same time the mean air flow is directed southward as atmospheric soundings reveal. Above the central city area those flows meet and lock polluted air. The strong radiative inversion, seen both in the model and in the data from Geophysical Institute, prevent normal air mixing in the deep layer. The inversion top is clearly seen on the photo as the height of improved visibility.
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Papers by Igor Esau
tion in the local stagnation zones. The simulated concentra- tions were larger than the concentrations obtained only due to the local PM2.5 emission, thus indicating dominant trans- boundary contribution of pollutants for other districts. We demonstrate how the source of critical pollution can be at-
tributed through model disaggregation of emission from spe- cific districts. The study reveals a decisive role of local air circulations over complex terrain that makes high-resolution modeling indispensable for adequate management of the ur- ban air quality. This modeling study has important policy-related implica-
tions. Uneven spatial distribution of the pollutants suggests prioritizing certain limited urban districts in policy scenarios. We show that focused efforts towards stove replacement in specific areas may have a dominant positive effect on the air quality in the whole municipality. The case study identifies urban districts where limited incentives would result in the strongest reduction of the population’s exposure to PM2.5.
tion in the local stagnation zones. The simulated concentra- tions were larger than the concentrations obtained only due to the local PM2.5 emission, thus indicating dominant trans- boundary contribution of pollutants for other districts. We demonstrate how the source of critical pollution can be at-
tributed through model disaggregation of emission from spe- cific districts. The study reveals a decisive role of local air circulations over complex terrain that makes high-resolution modeling indispensable for adequate management of the ur- ban air quality. This modeling study has important policy-related implica-
tions. Uneven spatial distribution of the pollutants suggests prioritizing certain limited urban districts in policy scenarios. We show that focused efforts towards stove replacement in specific areas may have a dominant positive effect on the air quality in the whole municipality. The case study identifies urban districts where limited incentives would result in the strongest reduction of the population’s exposure to PM2.5.