scholarly journals The Source, Size and Chemical Composition of the Winter Arctic Tropospheric Aerosol Layer Observed by Lidar at Eureka, Canada.

2001 ◽  
Vol 79 (1) ◽  
pp. 61-78 ◽  
Author(s):  
S. Ishii ◽  
T. Shibata ◽  
T. Sakai ◽  
M. Kido ◽  
K. Hara ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Source Size ◽  
Aerosol Layer ◽  
Tropospheric Aerosol

scholarly journals One year of Raman lidar observations of free-tropospheric aerosol layers over South Africa

2015 ◽  
Vol 15 (10) ◽  
pp. 5429-5442 ◽  
Author(s):  
E. Giannakaki ◽  
A. Pfüller ◽  
K. Korhonen ◽  
T. Mielonen ◽  
L. Laakso ◽  
...  
Keyword(s):  
South Africa ◽  
Optical Properties ◽  
Biomass Burning ◽  
Mean Value ◽  
Aerosol Layer ◽  
Raman Lidar ◽  
Tropospheric Aerosol ◽  
Wide Range ◽  
Significant Difference ◽  
532 Nm

Abstract. Raman lidar data obtained over a 1 year period has been analysed in relation to aerosol layers in the free troposphere over the Highveld in South Africa. In total, 375 layers were observed above the boundary layer during the period 30 January 2010 to 31 January 2011. The seasonal behaviour of aerosol layer geometrical characteristics, as well as intensive and extensive optical properties were studied. The highest centre heights of free-tropospheric layers were observed during the South African spring (2520 ± 970 m a.g.l., also elsewhere). The geometrical layer depth was found to be maximum during spring, while it did not show any significant difference for the rest of the seasons. The variability of the analysed intensive and extensive optical properties was high during all seasons. Layers were observed at a mean centre height of 2100 ± 1000 m with an average lidar ratio of 67 ± 25 sr (mean value with 1 standard deviation) at 355 nm and a mean extinction-related Ångström exponent of 1.9 ± 0.8 between 355 and 532 nm during the period under study. Except for the intensive biomass burning period from August to October, the lidar ratios and Ångström exponents are within the range of previous observations for urban/industrial aerosols. During Southern Hemispheric spring, the biomass burning activity is clearly reflected in the optical properties of the observed free-tropospheric layers. Specifically, lidar ratios at 355 nm were 89 ± 21, 57 ± 20, 59 ± 22 and 65 ± 23 sr during spring (September–November), summer (December–February), autumn (March–May) and winter (June–August), respectively. The extinction-related Ångström exponents between 355 and 532 nm measured during spring, summer, autumn and winter were 1.8 ± 0.6, 2.4 ± 0.9, 1.8 ± 0.9 and 1.8 ± 0.6, respectively. The mean columnar aerosol optical depth (AOD) obtained from lidar measurements was found to be 0.46 ± 0.35 at 355 nm and 0.25 ± 0.2 at 532 nm. The contribution of free-tropospheric aerosols on the AOD had a wide range of values with a mean contribution of 46%.

scholarly journals High-resolution optical constants of crystalline ammonium nitrate for infrared remote sensing of the Asian Tropopause Aerosol Layer

2020 ◽  
Author(s):  
Robert Wagner ◽  
Baptiste Testa ◽  
Michael Höpfner ◽  
Alexei Kiselev ◽  
Ottmar Möhler ◽  
...  
Keyword(s):  
Ammonium Nitrate ◽  
Optical Constants ◽  
Asian Summer Monsoon ◽  
Complex Refractive Index ◽  
Extinction Spectrum ◽  
Stable Phase ◽  
Aerosol Layer ◽  
Data Set ◽  
Tropospheric Aerosol ◽  
Infrared Measurements

Abstract. Infrared spectroscopic observations have shown that crystalline ammonium nitrate (AN) particles are an abundant constituent of the upper tropospheric aerosol layer which is formed during the Asian summer monsoon period, the so-called Asian Tropopause Aerosol Layer (ATAL). At upper tropospheric temperatures, the thermodynamically stable phase of AN is different from that at 298 K, meaning that presently available room-temperature optical constants of AN, that is, the real and imaginary parts of the complex refractive index, cannot be applied for the quantitative analysis of these infrared measurements. In this work, we have retrieved the first low-temperature data set of optical constants for crystalline AN in the 800–6000 cm−1 wavenumber range with a spectral resolution of 0.5 cm−1. The optical constants were iteratively derived from an infrared extinction spectrum of 1 micrometer-sized AN particles suspended in a cloud chamber at 223 K. The uncertainties of the new data set were carefully assessed in a comprehensive sensitivity analysis. We show that our data accurately fit aircraft-borne infrared measurements of ammonium nitrate particles in the ATAL.

scholarly journals Transport of Po Valley aerosol pollution to the northwestern Alps – Part 2: Long-term impact on air quality

2019 ◽  
Author(s):  
Henri Diémoz ◽  
Gian Paolo Gobbi ◽  
Tiziana Magri ◽  
Giordano Pession ◽  
Sara Pittavino ◽  
...  
Keyword(s):  
Air Quality ◽  
Chemical Composition ◽  
Weather Prediction ◽  
Urban Site ◽  
Aerosol Layer ◽  
Aerosol Transport ◽  
Po Valley ◽  
Aerosol Mass Concentration ◽  
The Impact ◽  
Aerosol Properties

Abstract. This work evaluates the impact of trans-regional aerosol transport from the polluted Po basin on particulate matter levels (PM10) and physico-chemical characteristics in the northwestern Alps. To this purpose, we exploited a multi-sensor, multiplatform database over a 3-years period (2015–2017) accompanied by a series of numerical simulations. The experimental setup included operational (24/7) vertically-resolved aerosol profiles by an Automated LiDAR-Ceilometer (ALC), verticallyintegrated aerosol properties by a sun/sky photometer, and surface measurements of aerosol mass concentration, size distribution and chemical composition. This experimental set of observations was then complemented by modelling tools, including Numerical Weather Prediction (NWP), Trajectory Statistical (TSM) and Chemical Transport (CTM) models, plus Positive Matrix Factorisation (PMF) on both the PM10 chemical speciation analyses and size distributions. In a first companion study (Diémoz et al., 2019), we showed and discussed through detailed case studies the 4-D phenomenology of recurrent episodes of aerosol transport from the polluted Po basin to the northwestern Italian Alps, and particularly to the Aosta Valley. Here we draw more general and statistically significant conclusions on the frequency of occurrence of this phenomenon, and on the quantitative impact of this regular, wind-driven, aerosol-rich atmospheric tide on PM10 air quality levels in this alpine environment. Combining vertically-resolved ALC measurements with wind information, we found that an advected aerosol layer is observed at the receptor site (Aosta) in 93 % of days characterized by easterly winds (thermally-driven winds from the plain or synoptic circulation regimes), and that the longer the time spent by air masses over the Po plain the higher this probability. On a seasonal basis, frequency of advected aerosol layers from the Po basin maximises in summer (70 % of the days classified using the ALC profiles) and minimises in winter and spring (57 % of the classified days). Duration of these advection events ranges from few hours up to several days, while aerosol layer thickness ranges from 500 up to 4000 m. This phenomenon was found to largely impact both surface levels and column-integrated aerosol properties, with PM10 and AOD values respectively increasing up to a factor of 3.5 and 4 in dates under the Po Valley influence. Similar variations in PM10 values observed at different stations within the Aosta Valley also indicated the phenomenon to act at the regional scale and to be related to non-local emissions. Pollution transport events were also shown to modify the mean chemical composition and typical size of particles in the target region. In fact, increase in secondary species, and mainly nitrate- and sulfate-rich components, were found to be effective proxies of the advections, with the transported aerosol responsible for at least 25 % of the PM10 measured in the urban site of Aosta, and adding up to over 50 μg m−3 during specific episodes, thus exceeding alone the EU established daily limit. This percentage is expected to be higher in the rural, pristine areas on the northwestern Alps, where chemical data were not available and trans-boundary contribution to PM10 might thus exceed the local one. Advected aerosols were also found to be on average finer, more light-scattering and more hygroscopic than the locally-produced ones. From a modelling point of view, our CTM simulations performed over a full year showed that the model is able to reproduce the phenomenon but underestimates its impact on PM10 levels. As a sensitivity test, we employed the ALC-derived identification of aerosol advections to re-weight the emissions from outside the boundaries of the regional domain in order to match the observed PM10 field. This simplified exercise indicated that an increase of such external emissions by a factor of 4 in the model would reduce the PM10 mean bias forecasts error (MBE) from −10 μg m−3 to less than 2 μg m−3, the normalised mean standard deviation (NMSD) from over −50 % to less than −10 % and would halve the model PM10 maximum deviations.

Typisation of the chemical composition of the tropospheric aerosol of the south of Western Siberia by the air mass

2018 ◽  
Author(s):  
Denis V. Simonenkov ◽  
Boris D. Belan ◽  
Georgii A. Ivlev ◽  
Artem V. Kozlov ◽  
Tatyana M. Rasskazchikova ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Western Siberia ◽  
The South ◽  
Air Mass ◽  
Tropospheric Aerosol

scholarly journals Improved SAGE II cloud/aerosol categorization and observations of the Asian tropopause aerosol layer: 1989–2005

2013 ◽  
Vol 13 (9) ◽  
pp. 4605-4616 ◽  
Author(s):  
L. W. Thomason ◽  
J.-P. Vernier
Keyword(s):  
Extinction Coefficient ◽  
Stratospheric Aerosol ◽  
Trace Gas ◽  
Data Sets ◽  
Aerosol Layer ◽  
Volcanic Origin ◽  
New Approach ◽  
Upper Troposphere ◽  
Volcanic Material ◽  
Tropospheric Aerosol

Abstract. We describe the challenges associated with the interpretation of extinction coefficient measurements by the Stratospheric Aerosol and Gas Experiment (SAGE II) in the presence of clouds. In particular, we have found that tropospheric aerosol analyses are highly dependent on a robust method for identifying when clouds affect the measured extinction coefficient. Herein, we describe an improved cloud identification method that appears to capture cloud/aerosol events more effectively than early methods. In addition, we summarize additional challenges to observing the Asian Tropopause Aerosol Layer (ATAL) using SAGE II observations. Using this new approach, we perform analyses of the upper troposphere, focusing on periods in which the UTLS (upper troposphere/lower stratosphere) is relatively free of volcanic material (1989–1990 and after 1996). Of particular interest is the Asian monsoon anticyclone where CALIPSO (Cloud-Aerosol Lidar Pathfinder Satellite Observations) has observed an aerosol enhancement. This enhancement, called the ATAL, has a similar morphology to observed enhancements in long-lived trace gas species like CO. Since the CALIPSO record begins in 2006, the question of how long this aerosol feature has been present requires a new look at the long-lived SAGE II data sets despite significant hurdles to its use in the subtropical upper troposphere. We find that there is no evidence of ATAL in the SAGE II data prior to 1998. After 1998, it is clear that aerosol in the upper troposphere in the ATAL region is substantially enhanced relative to the period before that time. In addition, the data generally supports the presence of the ATAL beginning in 1999 and continuing through the end of the mission, though some years (e.g., 2003) are complicated by the presence of episodic enhancements most likely of volcanic origin.

scholarly journals Tropospheric aerosol profile information from high-resolution oxygen A-band measurements from space

2015 ◽  
Vol 8 (2) ◽  
pp. 859-874 ◽  
Author(s):  
A. Geddes ◽  
H. Bösch
Keyword(s):  
Boundary Layer ◽  
Information Content ◽  
High Signal ◽  
Aerosol Layer ◽  
Free Troposphere ◽  
Limited Information ◽  
Aerosol Distribution ◽  
Spatial Coverage ◽  
Tropospheric Aerosol ◽  
Satellite Sensors

Abstract. Aerosols are an important factor in the Earth climatic system and they play a key role in air quality and public health. Observations of the oxygen A-band at 760 nm can provide information on the vertical distribution of aerosols from passive satellite sensors that can be of great interest for operational monitoring applications with high spatial coverage if the aerosol information is obtained with sufficient precision, accuracy and vertical resolution. To address this issue, retrieval simulations of the aerosol vertical profile retrieval from O2 A-band observations by GOSAT, the upcoming Orbiting Carbon Observatory-2 (OCO-2) and Sentinel 5-P missions, and the proposed CarbonSat mission have been carried out. Precise retrievals of aerosol optical depth (AOD) within the boundary layer were found to favour low-resolution, high signal-to-noise instruments such as Sentinel-5 P, whereas higher-resolution instruments such as OCO-2 showed greater performance at higher altitudes and in information content above the boundary layer. Retrieval of the AOD in the 0–2 km range with precision appears difficult from all studied instruments and the retrieval errors typically exceed a value of 0.05 for AODs up to 0.3. Constraining the surface albedo is a promising and effective way of improving the retrieval of aerosol, but the accuracy of the required prior knowledge is very high. Due to the limited information content of the aerosol profile retrieval, the use of a parameterised aerosol distribution is assessed, and we show that the AOD and height of an aerosol layer can be retrieved well if the aerosol layer is uplifted to the free troposphere; however, errors are often large for aerosol layers in the boundary layer. Additional errors are introduced by incorrect assumptions on surface pressure and aerosol mixture, which can both bias retrieved AOD and height by up to 45%. In addition, assumptions of the boundary layer temperature are found to yield an additional error of up to 8%. We conclude that the aerosol profile retrievals from O2 A-band using existing or upcoming satellite sensors will only provide limited information on aerosols in the boundary layer but such observations can be of great value for observing and mapping aerosol plumes in the free troposphere.

scholarly journals Nabro volcano aerosol in the stratosphere over Georgia, South Caucasus from ground-based spectrometry of twilight sky brightness

2013 ◽  
Vol 6 (10) ◽  
pp. 2563-2576 ◽  
Author(s):  
N. Mateshvili ◽  
D. Fussen ◽  
G. Mateshvili ◽  
I. Mateshvili ◽  
F. Vanhellemont ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Multiple Scattering ◽  
Optical Depth ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Spectral Measurements ◽  
South Caucasus ◽  
Tropospheric Aerosol ◽  
Sky Brightness

Abstract. Ground-based spectral measurements of twilight sky brightness were carried out between September 2009 and August 2011 in Georgia, South Caucasus. The algorithm which allowed to retrieve the lower stratospheric and upper tropospheric aerosol extinction profiles was developed. The Monte-Carlo technique was used to correctly represent multiple scattering in a spherical atmosphere. The estimated stratospheric aerosol optical depths at a wavelength of 780 nm were: 6 × 10−3 ± 2 × 10−3 (31 August 2009–29 November 2009), 2.5 × 10−3 ± 7 × 10−4 (20 March 2010–15 January 2011) and 8 × 10−3 ± 3 × 10−3 (18 July 2011–3 August 2011). The optical depth values correspond to the moderately elevated stratospheric aerosol level after the Sarychev eruption in 2009, background stratospheric aerosol layer, and the volcanically disturbed stratospheric aerosol layer after the Nabro eruption in June 2011.

scholarly journals Observations and hypotheses related to low to middle free tropospheric aerosol, water vapor and altocumulus cloud layers within convective weather regimes: A SEAC4RS case study

2019 ◽  
Author(s):  
Jeffrey S. Reid ◽  
Derek J. Posselt ◽  
Kathleen Kaku ◽  
Robert A. Holz ◽  
Gao Chen ◽  
...  
Keyword(s):  
Water Vapor ◽  
Atmospheric Composition ◽  
High Spectral Resolution ◽  
Aerosol Layer ◽  
In Situ Data ◽  
Tropospheric Aerosol ◽  
Entrainment Zone ◽  
Research Aircraft ◽  
Cumulus Congestus ◽  
Aerosol Emissions

Abstract. The NASA Studies of Emissions & Atmospheric Composition, Clouds & Climate Coupling by Regional Surveys (SEAC4RS) project included goals related to aerosol particle lifecycle in convective regimes. Using the University of Wisconsin High Spectral Resolution Lidar system at Huntsville, Alabama USA and the NASA DC-8 research aircraft, we investigate the altitude dependence of aerosol, water vapor and Altocumulus (Ac) properties in the free troposphere from a canonical August 12, 2013 convective storm case as a segue to a presentation of a mission wide analysis. It stands to reason that any moisture detrainment from convection must have an associated aerosol layer. Modes of covariability between aerosol, water vapor and Ac are examined relative to the boundary layer entrainment zone, 0 °C level, and anvil, a region known to contain Ac clouds and a complex aerosol layering structure (Reid et al., 2017). Multiple aerosol layers in regions warmer than 0 °C were observed within the PBL entrainment zone. At 0 °C there is a proclivity for aerosol and water vapor detrainment from storms, in association with melting level Ac shelves. Finally, at temperatures colder than 0 °C, weak aerosol layers were identified above Cumulus congestus tops (~0 °C and ~ 20 °C). Stronger aerosol signals return in association with anvil outflow. In situ data suggest that detraining particles undergo aqueous phase or heterogeneous chemical or microphysical transformations, while at the same time larger particles are being scavenged at higher altitudes leading to enhanced nucleation. We conclude by discussing hypotheses regarding links to aerosol emissions and potential indirect effects on Ac clouds.

scholarly journals High-resolution optical constants of crystalline ammonium nitrate for infrared remote sensing of the Asian Tropopause Aerosol Layer

2021 ◽  
Vol 14 (3) ◽  
pp. 1977-1991
Author(s):  
Robert Wagner ◽  
Baptiste Testa ◽  
Michael Höpfner ◽  
Alexei Kiselev ◽  
Ottmar Möhler ◽  
...  
Keyword(s):  
Ammonium Nitrate ◽  
Optical Constants ◽  
Asian Summer Monsoon ◽  
Complex Refractive Index ◽  
Extinction Spectrum ◽  
Stable Phase ◽  
Aerosol Layer ◽  
Data Set ◽  
Tropospheric Aerosol ◽  
Infrared Measurements

Abstract. Infrared spectroscopic observations have shown that crystalline ammonium nitrate (AN) particles are an abundant constituent of the upper tropospheric aerosol layer which is formed during the Asian summer monsoon period, the so-called Asian Tropopause Aerosol Layer (ATAL). At upper tropospheric temperatures, the thermodynamically stable phase of AN is different from that at 298 K, meaning that presently available room-temperature optical constants of AN, that is, the real and imaginary parts of the complex refractive index, cannot be applied for the quantitative analysis of these infrared measurements. In this work, we have retrieved the first low-temperature data set of optical constants for crystalline AN in the 800–6000 cm−1 wavenumber range with a spectral resolution of 0.5 cm−1. The optical constants were iteratively derived from an infrared extinction spectrum of 1 µm sized AN particles suspended in a cloud chamber at 223 K. The uncertainties of the new data set were carefully assessed in a comprehensive sensitivity analysis. We show that our data accurately fit aircraft-borne infrared measurements of ammonium nitrate particles in the ATAL.

Chemical composition of the ATAL aerosol measured by in-situ particle mass spectrometry

2020 ◽  
Author(s):  
Oliver Appel ◽  
Andreas Hünig ◽  
Antonis Dragoneas ◽  
Sergej Molleker ◽  
Frank Drewnick ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Laser Ablation ◽  
Chemical Composition ◽  
Particle Diameter ◽  
Aerosol Layer ◽  
Aerosol Mass Spectrometer ◽  
High Particle ◽  
Aerosol Mass ◽  
Ionisation Mass Spectrometry

<p>The Asian Tropopause Aerosol Layer (ATAL) has been found to be an aerosol layer with exceptionally high particle number concentrations in the UT/LS altitude range. During the StratoClim 2017 field campaign in Nepal we deployed the novel in-situ aerosol mass spectrometer ERICA (ERC Instrument for Chemical composition of Aerosols). It combines the methods of laser ablation mass spectrometry with flash vaporization/electron impact ionisation mass spectrometry in a single instrument to analyse the chemical composition of individual aerosol particles or small particle ensembles in the particle diameter range from 100 nm to 2 µm.</p><p>The quantitative analysis shows a strong contribution of ammonium nitrate (AN) to the ATAL aerosol concentration. In this layer, the AN concentrations can be as high as 1.5 µg per standard cubic meter. We present the vertical distribution of the mass concentrations of AN as well as other contributing species like sulphate and organics.</p><p>The single particle data from the laser ablation module of ERICA show a distinct particle type with nitrate and sulphate ions without the typical components of primary aerosol (soot, dust, metals) within the ATAL, indicating that a significant fraction of the ATAL aerosol consists of secondary particles formed in the upper troposphere.</p>

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