Atmospheric Chemistry and Physics Discussions

Journal Information
EISSN : 1680-7375
Current Publisher: Copernicus GmbH (10.5194)

Latest articles in this journal

, Silke Groß
Atmospheric Chemistry and Physics Discussions pp 1-25; doi:10.5194/acp-2021-172-rc1

Abstract:
By inducing linear contrails and contrail cirrus, air traffic has a main impact on the ice cloud coverage and occurrence. During the COVID-19 pandemic the civil air traffic over Europe was significantly reduced: in March and April 2020 to about 80 % compared to the year before. This unique situation allows to study the effect of air traffic on cirrus clouds. This work investigates based on satellite lidar measurements if and how cirrus cloud properties and occurrence changed over Europe in the course of COVID-19. Cirrus cloud properties are analyzed for different years, which showed similar meteorological conditions for March and April as they were found for 2020. Comparing these years shows that the cirrus cloud occurrence was reduced by about 30 % with smaller cloud thicknesses found in April 2020. The average thickness of cirrus clouds was reduced to 1.18 km in April 2020 compared to a value of 1.40 km under normal conditions. In addition, the cirrus clouds measured in April 2020 possess smaller mean values of the particle linear depolarization ratio (PLDR) than the previous years at high significance level, especially at colder temperatures (T < −50 °C). The same exercises are extended to the observations over the United States of America and over China. Besides the regional discrimination of cirrus clouds, we reach the final summary that cirrus clouds show significant changes of depolarization ratios in both March and April over Europe, no changes in both months over China, and significant changes only in April over USA.
, , , Charles Smeltzer, Andrew Weinheimer, , , Edward A. Celarier, Russell W. Long, James J. Szykman, et al.
Atmospheric Chemistry and Physics Discussions pp 1-58; doi:10.5194/acp-2020-1193-ac2

Abstract:
Nitrogen oxides (NOx = NO + NO2) play a crucial role in the formation of ozone and secondary inorganic and organic aerosols, thus affecting human health, global radiation budget, and climate. The diurnal and spatial variations of NO2 are functions of emissions, advection, deposition, vertical mixing, and chemistry. Their observations, therefore, provide useful constraints in our understanding of these factors. We employ a Regional chEmical and trAnsport model (REAM) to analyze the observed temporal (diurnal cycles) and spatial distributions of NO2 concentrations and tropospheric vertical column densities (TVCDs) using aircraft in situ measurements, surface EPA Air Quality System (AQS) observations, as well as the measurements of TVCDs by satellite instruments (OMI: the Ozone Monitoring Instrument; and GOME-2A: Global Ozone Monitoring Experiment – 2A), ground-based Pandora, and the Airborne Compact Atmospheric Mapper (ACAM) instrument, in July 2011 during the DISCOVER-AQ campaign over the Baltimore-Washington region. The model simulations at 36- and 4-km resolutions are in reasonably good agreement with the temporospatial NO2 observations in the daytime. However, nighttime mixing in the model needs to be enhanced to reproduce the observed NO2 diurnal cycle in the model. Another discrepancy is that Pandora measured NO2 TVCDs show much less variation in the late afternoon than simulated in the model. Relative to the 36-km model simulations, the 4-km model results show larger biases compared to the observations due largely to the larger spatial variations of NO2 in the model when the spatial resolution is increased from 36 to 4 km, although the biases are often comparable to the ranges of the observations. The high-resolution aircraft ACAM observations show a more dispersed distribution of NO2 vertical column densities (VCDs) and lower VCDs in urban regions than 4-km model simulations, reflecting likely the spatial distribution bias of NOx emissions in the National Emissions Inventory (NEI) 2011 at high resolution.
, , , Charles Smeltzer, Andrew Weinheimer, , , Edward A. Celarier, Russell W. Long, James J. Szykman, et al.
Atmospheric Chemistry and Physics Discussions pp 1-58; doi:10.5194/acp-2020-1193-ac1

Abstract:
Nitrogen oxides (NOx = NO + NO2) play a crucial role in the formation of ozone and secondary inorganic and organic aerosols, thus affecting human health, global radiation budget, and climate. The diurnal and spatial variations of NO2 are functions of emissions, advection, deposition, vertical mixing, and chemistry. Their observations, therefore, provide useful constraints in our understanding of these factors. We employ a Regional chEmical and trAnsport model (REAM) to analyze the observed temporal (diurnal cycles) and spatial distributions of NO2 concentrations and tropospheric vertical column densities (TVCDs) using aircraft in situ measurements, surface EPA Air Quality System (AQS) observations, as well as the measurements of TVCDs by satellite instruments (OMI: the Ozone Monitoring Instrument; and GOME-2A: Global Ozone Monitoring Experiment – 2A), ground-based Pandora, and the Airborne Compact Atmospheric Mapper (ACAM) instrument, in July 2011 during the DISCOVER-AQ campaign over the Baltimore-Washington region. The model simulations at 36- and 4-km resolutions are in reasonably good agreement with the temporospatial NO2 observations in the daytime. However, nighttime mixing in the model needs to be enhanced to reproduce the observed NO2 diurnal cycle in the model. Another discrepancy is that Pandora measured NO2 TVCDs show much less variation in the late afternoon than simulated in the model. Relative to the 36-km model simulations, the 4-km model results show larger biases compared to the observations due largely to the larger spatial variations of NO2 in the model when the spatial resolution is increased from 36 to 4 km, although the biases are often comparable to the ranges of the observations. The high-resolution aircraft ACAM observations show a more dispersed distribution of NO2 vertical column densities (VCDs) and lower VCDs in urban regions than 4-km model simulations, reflecting likely the spatial distribution bias of NOx emissions in the National Emissions Inventory (NEI) 2011 at high resolution.
, Wonbae Bang, , , Chia-Lun Tsai, Eunsil Jung, GyuWon Lee
Atmospheric Chemistry and Physics Discussions pp 1-36; doi:10.5194/acp-2021-128-rc1

Abstract:
Snowfall in north-eastern part of South Korea is the result of complex snowfall mechanisms due to a highly-contrasting terrain combined with nearby warm waters and three synoptic pressure patterns. All these factors together create unique combinations, whose disentangling can provide new insights into the microphysics of snow in the planet. This study focuses on the impact of wind flow and topography on the microphysics drawing of twenty snowfall events during the ICE-POP 2018 (International Collaborative Experiment for Pyeongchang 2018 Olympic and Paralympic winter games) field campaign in the Gangwon region. The vertical structure of precipitation and size distribution characteristics are investigated with collocated MRR (Micro Rain Radar) and PARSIVEL (PARticle SIze VELocity) disdrometers installed across the mountain range. The results indicate that wind shear and embedded turbulence were the cause of the riming process dominating the mountainous region. As the strength of these processes weaken from the mountainous region to the coastal region, riming became less significant and gave way to aggregation. This study specifically analyzes the microphysical characteristics under three major synoptic patterns: air-sea interaction, cold low, and warm low. Air–sea interaction pattern is characterized by more frequent snowfall and vertically deeper precipitation systems in the windward side, resulting in significant aggregation in the coastal region, with riming featuring as a primary growth mechanism in both mountainous and coastal regions. The cold low pattern is characterized by a higher snowfall rate and vertically deep systems in mountainous region, with the precipitation system becoming shallower in the coastal region and strong turbulence being found in the layer below 2 km in the mountainous upstream region (linked with dominant aggregation). The warm low pattern features the deepest system: precipitation here is enhanced by the seeder–feeder mechanism with two different precipitation systems divided by the transition zone (easterly below and westerly above). Overall, it is found that strong shear and turbulence in the transition zone is a likely reason for the dominant riming process in mountainous region, with aggregation being important in both mountainous and coastal regions.
Sudip Chakraborty, , Hui Su, Rong Fu
Atmospheric Chemistry and Physics Discussions pp 1-27; doi:10.5194/acp-2020-1138-rc2

Abstract:
The boreal summer dry season length is reported to have been increasing in the last three decades over the Congo rainforest, which is the second-largest rainforest in the world. In some years, the wet season in boreal autumn starts early while in others it arrives late. The mechanism behind such a change in wet season onset date has not been investigated yet. Using multi-satellite datasets, we discover that the variation of aerosols in dry season plays a major role in determining the subsequent wet season onset. Dry season aerosol optical depth (AOD) influences the strength of the southern African easterly jet (AEJ-S) and thus the onset of the wet season. Higher AOD associated with a higher dust mass flux reduces the net downward shortwave radiation and decreases the surface temperature over the Congo rainforest region, leading to a stronger meridional temperature gradient between the rainforest and the Kalahari Desert as early as in June. The latter, in turn, strengthens the AEJ-S, sets in an early and a stronger easterly flow, leads to a stronger equatorward convergence and an early onset of the wet season in late August to early September. The mean AOD in the dry season over the region is strongly correlated (r =0.7) with the timing of the subsequent wet season onset. Conversely, in low AOD years, the onset of the wet season over the Congo basin is delayed to mid-October.
Christina Williamson, Matthew Ozon, , , Aku Seppänen, Kari E. J. Lehtinen
Atmospheric Chemistry and Physics Discussions pp 1-22; doi:10.5194/acp-2021-99-rc1

Abstract:
Bayesian state estimation in the form of Kalman smoothing was applied to Differential Mobility Analyser Train (DMA-train) measurements of aerosol size distribution dynamics. Four experiments were analysed in order to estimate the aerosol size distribution, formation rate and size-dependent growth rate, as functions of time. The first analysed case was a synthetic one, generated by a detailed aerosol dynamics model, and the other three chamber experiments performed at the CERN CLOUD facility. The estimated formation and growth rates were compared with other methods used earlier for the CLOUD data and with the true values for the computer-generated synthetic experiment. The agreement in the growth rates was remarkably good for all studied cases. The formation rates matched also well, especially considering the fact that they were estimated from data given by two different instruments, the other being the Particle Size magnifier (PSM). The presented Fixed Interval Kalman Smoother (FIKS) method has clear advantages compared with earlier methods that have been applied to this kind of data. First, FIKS can reconstruct the size distribution between possible size gaps in the measurement in such a way that it is consistent with aerosol size distribution dynamics theory, and second, the method gives rise to direct and reliable estimation of size distribution and process rate uncertainties if the uncertainties in the kernel functions and numerical models are known.
Atmospheric Chemistry and Physics Discussions pp 1-27; doi:10.5194/acp-2021-86-rc2

Abstract:
Worldwide air quality has worsened in the last decades as a consequence of increased anthropogenic emissions, in particular from the sector of power generation. The evidence of the effects of atmospheric pollution (and particularly fine particulate matter, PM2.5) on human health is unquestionable nowadays, producing mainly cardiovascular and respiratory diseases, morbidity and even mortality. These effects can even enhance in the future as a consequence of climate penalties and future changes in the population projected. Because of all these reasons, the main objective of this contribution is the estimation of annual excess premature deaths (PD) associated to PM2.5 on present (1991–2010) and future (2031–2050) European population by using non-linear exposure-response functions. The endpoints included are Lung Cancer (LC), Chronic Obstructive Pulmonary Disease (COPD), Low Respiratory Infections (LRI), Ischemic Heart Disease (IHD), cerebrovascular disease (CEV) and other Non-Communicable Diseases (other NCD). PM2.5 concentrations come from coupled chemistry-climate regional simulations under present and RCP8.5 future scenarios. The cases assessed include the estimation of the present incidence of PD (PRE-P2010), the quantification of the role of a changing climate on PD (FUT-P2010) and the importance of changes in the population projected for the year 2050 on the incidence of excess PD (FUT-P2050). Two additional cases (REN80-P2010 and REN80-P2050) evaluate the impact on premature mortality rates of a mitigation scenario in which the 80 % of European energy production comes from renewables sources. The results indicate that PM2.5 accounts for nearly 895,000 [95 % confidence interval (95 % CI) 725,000-1,056,000] annual excess PD over Europe, with IHD being the largest contributor to premature mortality associated to fine particles in both present and future scenarios. The case isolating the effects of climate penalty (FUT-P2010) estimates a variation +0.2 % on mortality rates over the whole domain. However, under this scenario the incidence of PD over central Europe will benefit from a decrease of PM2.5 (−2.2 PD/100,000 h.) while in eastern (+1.3 PD/100,000 h.) and western (+0.4 PD/100,000 h.) Europe PD will increase due to increased PM2.5 levels. The changes in the projected population (FUT-P2050) will lead to a large increase of annual excess PD (1,540,000, 95 % CI 1,247,000-1,818,000), +71.96 % with respect to PRE-P2010 and +71.67 % to FUT-P2010) due to the aging of the European population. Last, the mitigation scenario (REN80-P2050) demonstrates that the effects of a mitigation policy increasing the ratio of renewable sources in the energy mix energy could lead to a decrease of over 60,000 (95 % CI 48,500-70,900) annual PD for the year 2050 (a decrease of −4 % in comparison with the no-mitigation scenario, FUT-P2050). In spite of the uncertainties inherent to future estimations, this contribution reveals the need of the governments and public entities to take action and bet for air pollution mitigation policies.
Zane Dedekind, , Sylvaine Ferrachat,
Atmospheric Chemistry and Physics Discussions pp 1-27; doi:10.5194/acp-2020-1326-ac1

Abstract:
The discrepancy between the observed concentration of ice nucleating particles (INPs) and the ice crystal number concentration (ICNC) remains unresolved and limits our understanding of ice formation and hence precipitation amount, location and intensity. Enhanced ice formation through secondary ice production (SIP) could be accounting for this discrepancy. Here, we present the results from a sensitivity model study in the Eastern Swiss Alps with additional simulated in-cloud SIP on precipitation formation and consequently on surface precipitation. The SIP processes considered include rime splintering, droplet shattering during freezing and breakup through ice-ice collisions. We simulated the passage of a cold front at Gotschnagrat, a peak at 2281 m above sea level (a.s.l.), on 7 March 2019 with COSMO, at a 1 km horizontal resolution, as part of the RACLETS field campaign in the Davos region in Switzerland. The largest simulated difference in the ICNC at the surface originated from the breakup simulations. Indeed, breakup caused a 1 to 3 order of magnitude increase in the ICNC compared to SIP from rime splintering or without SIP processes in the control simulations. The ICNCs from the collisional breakup simulations at Gotschnagrat were in better agreement with the ICNCs measured on a gondola near the surface. However, these simulations were not able to reproduce the ice crystal habits near the surface. Enhanced ICNCs from collisional breakup reduced localized regions of higher precipitation and thereby improving the model performance in terms of surface precipitation over the domain.
Meike K. Rotermund, Vera Bense, , , , , Tilman Hüneke, Timo Keber, Flora Kluge, Benjamin Schreiner, et al.
Atmospheric Chemistry and Physics Discussions pp 1-53; doi:10.5194/acp-2021-202-cc1

Abstract:
We report on measurements of total bromine (Brtot) in the upper troposphere and lower stratosphere taken during 15 flights with the German High Altitude and LOng range research aircraft (HALO). The research campaign WISE (Wave-driven ISentropic Exchange) included regions over the North Atlantic, Norwegian Sea and north-western Europe in fall 2017. Brtot is calculated from measured total organic bromine (Brorg) added to inorganic bromine (Bry inorg), evaluated from measured BrO and photochemical modelling. Combining these data, the weighted-mean [Brtot] is 19.2 ± 1.2 ppt in the northern hemispheric lower stratosphere (LS) in agreement with expectations for Brtot in the middle stratosphere (Engel and Rigby et al. (2018)). The data reflects the expected variability in Brtot in the LS due to variable influx of shorter-lived brominated source and product gases from different regions of entry. A closer look into Brorg and Bry inorg, as well as simultaneously measured transport tracers (CO and N2O) and an air mass lag-time tracer (SF6), suggests that bromine-rich air masses persistently protruded into the lowermost stratosphere (LMS) in boreal summer, creating a high bromine region (HBrR). A subsection, HBrR*, has a weighted average of [Brtot] = 20.9 ± 0.8 ppt. The most probable source region is former air from the tropical upper troposphere and tropopause layer (UT/TTL) with a weighted mean [Brtot] = 21.6 ± 0.7 ppt. CLaMS Lagrangian transport modelling shows that the HBrR air mass consists of 51.2 % from the tropical troposphere, 27.1 % from the stratospheric background, and 6.4 % from the mid-latitude troposphere (as well as contributions from other domains). The majority of the surface air reaching the HBrR is from the Asian monsoon and its adjacent tropical regions, which greatly influences trace gas transport into the LMS in boreal summer and fall. Tropical cyclones from Central America in addition to air associated with the Asian monsoon region contribute to the elevated Brtot observed in the UT/TTL. TOMCAT global 3–D model simulations of a concurrent increase of Brtot show an associated O3 change of −2.6 ± 0.7 % in the LS and −3.1 ± 0.7 % near the tropopause. Our study of varying Brtot in the LS also emphasizes the need for more extensive monitoring of stratospheric Brtot globally and seasonally to fully understand its impact on LMS O3 and its radiative forcing of climate, as well as in aged air in the middle stratosphere to elucidate the stratospheric trend in bromine.
Meike K. Rotermund, Vera Bense, , , , , Tilman Hüneke, Timo Keber, Flora Kluge, Benjamin Schreiner, et al.
Atmospheric Chemistry and Physics Discussions pp 1-53; doi:10.5194/acp-2021-202-ac1

Abstract:
We report on measurements of total bromine (Brtot) in the upper troposphere and lower stratosphere taken during 15 flights with the German High Altitude and LOng range research aircraft (HALO). The research campaign WISE (Wave-driven ISentropic Exchange) included regions over the North Atlantic, Norwegian Sea and north-western Europe in fall 2017. Brtot is calculated from measured total organic bromine (Brorg) added to inorganic bromine (Bry inorg), evaluated from measured BrO and photochemical modelling. Combining these data, the weighted-mean [Brtot] is 19.2 ± 1.2 ppt in the northern hemispheric lower stratosphere (LS) in agreement with expectations for Brtot in the middle stratosphere (Engel and Rigby et al. (2018)). The data reflects the expected variability in Brtot in the LS due to variable influx of shorter-lived brominated source and product gases from different regions of entry. A closer look into Brorg and Bry inorg, as well as simultaneously measured transport tracers (CO and N2O) and an air mass lag-time tracer (SF6), suggests that bromine-rich air masses persistently protruded into the lowermost stratosphere (LMS) in boreal summer, creating a high bromine region (HBrR). A subsection, HBrR*, has a weighted average of [Brtot] = 20.9 ± 0.8 ppt. The most probable source region is former air from the tropical upper troposphere and tropopause layer (UT/TTL) with a weighted mean [Brtot] = 21.6 ± 0.7 ppt. CLaMS Lagrangian transport modelling shows that the HBrR air mass consists of 51.2 % from the tropical troposphere, 27.1 % from the stratospheric background, and 6.4 % from the mid-latitude troposphere (as well as contributions from other domains). The majority of the surface air reaching the HBrR is from the Asian monsoon and its adjacent tropical regions, which greatly influences trace gas transport into the LMS in boreal summer and fall. Tropical cyclones from Central America in addition to air associated with the Asian monsoon region contribute to the elevated Brtot observed in the UT/TTL. TOMCAT global 3–D model simulations of a concurrent increase of Brtot show an associated O3 change of −2.6 ± 0.7 % in the LS and −3.1 ± 0.7 % near the tropopause. Our study of varying Brtot in the LS also emphasizes the need for more extensive monitoring of stratospheric Brtot globally and seasonally to fully understand its impact on LMS O3 and its radiative forcing of climate, as well as in aged air in the middle stratosphere to elucidate the stratospheric trend in bromine.
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