scholarly journals Aircraft Observations of Aerosol in the Manaus Urban Plume and Surrounding Tropical Forest during GoAmazon 2014/15

2018 ◽  
Author(s):  
John E. Shilling ◽  
Mikhail S. Pekour ◽  
Edward C. Fortner ◽  
Paulo Artaxo ◽  
Suzane de Sá ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Oxidation State ◽  
Biomass Burning ◽  
Urban Pollution ◽  
Organic Aerosol ◽  
Dry Season ◽  
Carbon Oxidation ◽  
Wet Season ◽  
The Mean ◽  
American Cities

Abstract. The Green Ocean Amazon (GoAmazon 2014/5) campaign, conducted from January 2014–December 2015 in the vicinity of Manaus, Brazil, was designed to study the aerosol lifecycle and aerosol-cloud interactions in both pristine and anthropogenically-influenced conditions. As part of this campaign, the U.S. Department of Energy (DOE) G-1 research aircraft was deployed from February 17–March 25, 2014 (wet season) and September 6–October 5, 2014 (dry season) to investigate aerosol and cloud properties aloft. Here, we present results from the G-1 deployments focusing on measurements of the aerosol chemical composition and discussion of aerosol sources and secondary organic aerosol formation and aging. In the first portion of the manuscript, we provide an overview of the data and compare and contrast the data from the wet and dry season. Organic aerosol (OA) dominates the deployment-averaged chemical composition, comprising 78 % of the non-refractory PM1 aerosol mass with sulfate comprising 13 %, nitrate 5 %, and ammonium 4 %. This product distribution was unchanged between seasons, despite the fact that total aerosol loading was significantly higher in the dry season and that regional and local biomass burning was a significant source of OA mass in the dry, but not wet, season. However, the OA was more oxidized in the dry season, with the median of the mean carbon oxidation state increasing from −0.45 in the wet season to −0.02 in the dry season. In the second portion of the manuscript, we discuss the evolution of the Manaus plume on March 13, 2014, one of the golden days in the wet season. On this flight, we observe a clear increase in OA concentrations in the Manaus plume relative to the background. As the plume is transported downwind and ages, we observe dynamic changes in the OA. The mean carbon oxidation state of the OA increases from −0.6 to −0.45 during the 4–5 hours of photochemical aging. Hydrocarbon-like organic aerosol (HOA) mass is lost with ΔHOA/ΔCO values decreasing from 17.6 μg/m3 ppmv−1 over Manaus to 10.6 μg/m3 ppmv−1 95 km downwind. Loss of HOA is balanced out by formation of oxygenated organic aerosol (OOA) with ΔOOA/ΔCO increasing from 9.2 to 23.1 μg/m3 ppmv−1. Because HOA loss is balanced by OOA formation, we observe little change in the net Δorg/ΔCO values; Δorg/ΔCO averages 31 μg/m3 ppmv−1 and does not increase with aging. Our observation of constant Δorg/ΔCO are in contrast to literature studies of the outflow of several North American cities, which report significant increases in Δorg/ΔCO for the first day of plume aging. These observations suggest that SOA formation in the Manaus plume occurs, at least in part, by a different mechanism than observed in urban outflow plumes in most other literature studies. Constant Δorg/ΔCO with plume aging has been observed in many biomass burning plumes, but we are unaware of reports of fresh urban emissions aging in this manner. These observations show that urban pollution emitted from Manaus in the wet season forms much less particulate downwind than urban pollution emitted from North American cities.

scholarly journals Aircraft observations of the chemical composition and aging of aerosol in the Manaus urban plume during GoAmazon 2014/5

2018 ◽  
Vol 18 (14) ◽  
pp. 10773-10797 ◽  
Author(s):  
John E. Shilling ◽  
Mikhail S. Pekour ◽  
Edward C. Fortner ◽  
Paulo Artaxo ◽  
Suzane de Sá ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Oxidation State ◽  
Biomass Burning ◽  
Urban Pollution ◽  
Organic Aerosol ◽  
Dry Season ◽  
Carbon Oxidation ◽  
Wet Season ◽  
The Mean ◽  
American Cities

Abstract. The Green Ocean Amazon (GoAmazon 2014/5) campaign, conducted from January 2014 to December 2015 in the vicinity of Manaus, Brazil, was designed to study the aerosol life cycle and aerosol–cloud interactions in both pristine and anthropogenically influenced conditions. As part of this campaign, the U.S. Department of Energy (DOE) Gulfstream 1 (G-1) research aircraft was deployed from 17 February to 25 March 2014 (wet season) and 6 September to 5 October 2014 (dry season) to investigate aerosol and cloud properties aloft. Here, we present results from the G-1 deployments focusing on measurements of the aerosol chemical composition and secondary organic aerosol (SOA) formation and aging. In the first portion of the paper, we provide an overview of the data and compare and contrast the data from the wet and dry season. Organic aerosol (OA) dominates the deployment-averaged chemical composition, comprising 80 % of the non-refractory PM1 aerosol mass, with sulfate comprising 14 %, nitrate 2 %, and ammonium 4 %. This product distribution was unchanged between seasons, despite the fact that total aerosol loading was significantly higher in the dry season and that regional and local biomass burning was a significant source of OA mass in the dry, but not wet, season. However, the OA was more oxidized in the dry season, with the median of the mean carbon oxidation state increasing from −0.45 in the wet season to −0.02 in the dry season. In the second portion of the paper, we discuss the evolution of the Manaus plume, focusing on 13 March 2014, one of the exemplary days in the wet season. On this flight, we observe a clear increase in OA concentrations in the Manaus plume relative to the background. As the plume is transported downwind and ages, we observe dynamic changes in the OA. The mean carbon oxidation state of the OA increases from −0.6 to −0.45 during the 4–5 h of photochemical aging. Hydrocarbon-like organic aerosol (HOA) mass is lost, with ΔHOA∕ΔCO values decreasing from 17.6 µg m−3 ppmv−1 over Manaus to 10.6 µg m−3 ppmv−1 95 km downwind. Loss of HOA is balanced out by formation of oxygenated organic aerosol (OOA), with ΔOOA∕ΔCO increasing from 9.2 to 23.1 µg m−3 ppmv−1. Because hydrocarbon-like organic aerosol (HOA) loss is balanced by OOA formation, we observe little change in the net Δorg∕ΔCO values; Δorg∕ΔCO averages 31 µg m−3 ppmv−1 and does not increase with aging. Analysis of the Manaus plume evolution using data from two additional flights in the wet season showed similar trends in Δorg∕ΔCO to the 13 March flight; Δorg∕ΔCO values averaged 34 µg m−3 ppmv−1 and showed little change over 4–6.5 h of aging. Our observation of constant Δorg∕ΔCO are in contrast to literature studies of the outflow of several North American cities, which report significant increases in Δorg∕ΔCO for the first day of plume aging. These observations suggest that SOA formation in the Manaus plume occurs, at least in part, by a different mechanism than observed in urban outflow plumes in most other literature studies. Constant Δorg∕ΔCO with plume aging has been observed in many biomass burning plumes, but we are unaware of reports of fresh urban emissions aging in this manner. These observations show that urban pollution emitted from Manaus in the wet season forms less particulate downwind as it ages than urban pollution emitted from North American cities.

scholarly journals Chemical composition, main sources and temporal variability of PM<sub>1</sub> aerosols in southern African grassland

2013 ◽  
Vol 13 (6) ◽  
pp. 15517-15566 ◽  
Author(s):  
P. Tiitta ◽  
V. Vakkari ◽  
M. Josipovic ◽  
P. Croteau ◽  
J. P. Beukes ◽  
...  
Keyword(s):  
South Africa ◽  
Chemical Composition ◽  
Source Region ◽  
Organic Aerosols ◽  
Organic Aerosol ◽  
Dry Season ◽  
Wet Season ◽  
Air Mass ◽  
Air Masses ◽  
Source Regions

Abstract. Southern Africa is a significant source region of atmospheric pollution, yet long-term data on pollutant concentrations and properties from this region are rather limited. A recently established atmospheric measurement station in South Africa, Welgegund, is strategically situated to capture regional background emissions, as well as emissions from the major source regions in the interior of South Africa. We measured non-refractive submicron aerosols (NR-PM1) and black carbon over a one year period in Welgegund, and investigated the seasonal and diurnal patterns of aerosol concentration levels, chemical composition, acidity and oxidation level. Based on air mass back trajectories, four distinct source regions were determined for NR-PM1. Supporting data utilized in our analysis included particle number size distributions, aerosol absorption, trace gas concentrations, meteorological variables and the flux of carbon dioxide. The dominant submicron aerosol constituent during the dry season was organic aerosol, reflecting high contribution from savannah fires and other combustion sources. Organic aerosol concentrations were lower during the wet season, presumably due to wet deposition as well as reduced emissions from combustion sources. Sulfate concentrations were usually high and exceeded organic aerosol concentrations when air-masses were transported over regions containing major point sources. Sulfate and nitrate concentrations peaked when air masses passed over the industrial Highveld (iHV) area. In contrast, concentrations were much lower when air masses passed over the cleaner background (BG) areas. Air masses associated with the anti-cyclonic recirculation (ACBIC) source region contained largely aged OA. Positive Matrix Factorization (PMF) analysis of aerosol mass spectra was used to characterize the organic aerosol (OA) properties. The factors identified were oxidized organic aerosols (OOA) and biomass burning organic aerosols (BBOA) in the dry season and low-volatile (LV-OOA) and semi-volatile (SV-OOA) organic aerosols in the wet season. The results highlight the importance of primary BBOA in the dry season, which represented (33% of the total OA and peaked when air mass passed over the highly populated and industrialized region (iHV). The significance of aerosol acidity on the evolution of OOA was also discussed.

scholarly journals Chemical composition, main sources and temporal variability of PM<sub>1</sub> aerosols in southern African grassland

2014 ◽  
Vol 14 (4) ◽  
pp. 1909-1927 ◽  
Author(s):  
P. Tiitta ◽  
V. Vakkari ◽  
P. Croteau ◽  
J. P. Beukes ◽  
P. G. van Zyl ◽  
...  
Keyword(s):  
South Africa ◽  
Chemical Composition ◽  
Source Region ◽  
Organic Aerosols ◽  
Organic Aerosol ◽  
Dry Season ◽  
Wet Season ◽  
Air Masses ◽  
Source Regions ◽  
Combustion Sources

Abstract. Southern Africa is a significant source region of atmospheric pollution, yet long-term data on pollutant concentrations and properties from this region are rather limited. A recently established atmospheric measurement station in South Africa, Welgegund, is strategically situated to capture regional background concentrations, as well as emissions from the major source regions in the interior of South Africa. We measured non-refractive submicron aerosols (NR-PM1) and black carbon over a one year period in Welgegund, and investigated the seasonal and diurnal patterns of aerosol concentration levels, chemical composition, acidity and oxidation level. Based on air mass back trajectories, four distinct source regions were determined for NR-PM1. Supporting data utilised in our analysis included particle number size distributions, aerosol absorption, trace gas concentrations, meteorological variables and the flux of carbon dioxide. The dominant submicron aerosol constituent during the dry season was organic aerosol, reflecting high contribution from savannah fires and other combustion sources. Organic aerosol concentrations were lower during the wet season, presumably due to wet deposition as well as reduced emissions from combustion sources. Sulfate concentrations were usually high and exceeded organic aerosol concentrations when air-masses were transported over regions containing major point sources. Sulfate and nitrate concentrations peaked when air masses passed over the industrial Highveld (iHV) area. In contrast, concentrations were much lower when air masses passed over the cleaner background (BG) areas. Air masses associated with the anti-cyclonic recirculation (ACBIC) source region contained largely aged OA. Positive Matrix Factorization (PMF) analysis of aerosol mass spectra was used to characterise the organic aerosol (OA) properties. The factors identified were oxidized organic aerosols (OOA) and biomass burning organic aerosols (BBOA) in the dry season and low-volatile (LV-OOA) and semi-volatile (SV-OOA) organic aerosols in the wet season. The results highlight the importance of primary BBOA in the dry season, which represented 33% of the total OA. Aerosol acidity and its potential impact on the evolution of OOA are also discussed.

scholarly journals Seasonal variations in PM10 inorganic composition in the Andean city

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Rasa Zalakeviciute ◽  
Katiuska Alexandrino ◽  
Yves Rybarczyk ◽  
Alexis Debut ◽  
Karla Vizuete ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Inductively Coupled Plasma ◽  
Chemical Elements ◽  
Large Fraction ◽  
Urban Pollution ◽  
Optical Emission ◽  
High Elevation ◽  
Water Soluble ◽  
Wet Season ◽  
Soluble Ions

Abstract Particulate matter (PM) is one of the key pollutants causing health risks worldwide. While the preoccupation for increased concentrations of these particles mainly depends on their sources and thus chemical composition, some regions are yet not well investigated. In this work the composition of chemical elements of atmospheric PM10 (particles with aerodynamic diameters ≤ 10 µm), collected at the urban and suburban sites in high elevation tropical city, were chemically analysed during the dry and wet seasons of 2017–2018. A large fraction (~ 68%) of PM10 composition in Quito, Ecuador is accounted for by water-soluble ions and 16 elements analysed using UV/VIS spectrophotometer and Inductively Coupled Plasma—Optical Emission Spectroscopy (ICP-OES). Hierarchical clustering analysis was performed to study a correlation between the chemical composition of urban pollution and meteorological parameters. The suburban area displays an increase in PM10 concentrations and natural elemental markers during the dry (increased wind intensity, resuspension of soil dust) season. Meanwhile, densely urbanized area shows increased total PM10 concentrations and anthropogenic elemental markers during the wet season, which may point to the worsened combustion and traffic conditions. This might indicate the prevalence of cardiovascular and respiratory problems in motorized areas of the cities in the developing world.

scholarly journals Processing of biomass burning aerosol in the Eastern Mediterranean during summertime

2013 ◽  
Vol 13 (10) ◽  
pp. 25969-25999 ◽  
Author(s):  
A. Bougiatioti ◽  
I. Stavroulas ◽  
E. Kostenidou ◽  
P. Zarmpas ◽  
C. Theodosi ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Biomass Burning ◽  
Eastern Mediterranean ◽  
Late Summer ◽  
Organic Aerosol ◽  
High Temporal Resolution ◽  
Night Time ◽  
Air Masses ◽  
Aerosol Mass ◽  
Atmospheric Processing

Abstract. The aerosol chemical composition in air masses affected by wildfires from the Greek islands of Chios, Euboea and Andros, the Dalmatian Coast and Sicily, during late summer of 2012 was characterized at the remote background site of Finokalia, Crete. Air masses were transported several hundreds of kilometers, arriving at the measurement station after approximately half a day of transport, mostly during night-time. The chemical composition of the particulate matter was studied by different high temporal resolution instruments, including an Aerosol Chemical Speciation Monitor (ACSM) and a seven-wavelength aethalometer. Despite the large distance from emission and long atmospheric processing, a clear biomass burning organic aerosol (BBOA) profile containing characteristic markers is derived from BC measurements and Positive Matrix Factorization (PMF) analysis of the ACSM mass spectra. The ratio of fresh to aged BBOA decreases with increasing atmospheric processing time and BBOA components appear to be converted to oxygenated organic aerosol (OOA). Given that the smoke was mainly transported overnight, it appears that the processing can take place in the dark. These results show that a significant fraction of the BBOA loses its characteristic AMS signature and is transformed to OOA in less than a day. This implies that biomass burning can contribute almost half of the organic aerosol mass in the area during summertime.

scholarly journals Investigation of Heavy Metals Level in selected Boreholes around the Vicinity of some Cemeteries in Benin City, Nigeria

2021 ◽  
Vol 25 (5) ◽  
pp. 841-845
Author(s):  
C.A.E. Ibhadode ◽  
I.R. Ilaboya
Keyword(s):  
Heavy Metals ◽  
Pollution Index ◽  
Mean Value ◽  
Dry Season ◽  
Wet Season ◽  
Monthly Basis ◽  
Benin City ◽  
Standard Procedures ◽  
The Mean ◽  
Mean Concentration

Groundwater pollution by heavy metals such as lead, copper, nickel and iron is one of the major environmental issues of concern which has developed into a widely studied area. In this study, attempt was made to investigate the level of heavy metals in selected boreholes around the vicinity of cemeteries in Benin City. Seventy-two (72) samples of groundwater were taken from boreholes in 9 stations around the three cemeteries in Benin City on monthly basis. The samples were analysed for 7 heavy metals, in accordance with standard procedures. The heavy metals include; Zinc, Lead Iron, Copper, Cadmium, Nickel and Mercury. From the results of the study, a variation in the mean concentration of zinc was observed. The mean concentration of zinc in site 1 was 0.450mg/l, for site 2, it was 0.140mg/l and for site 3, it was 1.0533mg/l. For iron, mean concentration was 0.072mg/l in site 1. For site 2, mean concentration of iron was 2.140mg/l and for site 3, mean concentration of iron was 0.560mg/l. It was further revealed based on the results that mean value of heavy metals in groundwater around cemeteries in Benin City were generally lower during dry season compared to wet season. In addition, result of computed pollution index (Pi) revealed that the heavy metal with the highest potential to pollute groundwater is Cadmium, with Pi of 0.5333 and 0.400 representing dry season and wet season respectively.

Trace gases and organic aerosol at a rural site in Vietnam during large scale biomass burning

2021 ◽  
Author(s):  
Simone M. Pieber ◽  
Dac-Loc Nguyen ◽  
Hendryk Czech ◽  
Stephan Henne ◽  
Nicolas Bukowiecki ◽  
...  
Keyword(s):  
Air Quality ◽  
Chemical Composition ◽  
Biomass Burning ◽  
Large Scale ◽  
Trace Gases ◽  
Organic Aerosol ◽  
Trace Gas ◽  
Rural Site ◽  
Air Masses ◽  
Mixing Ratios

&lt;p&gt;Open biomass burning (BB) is a globally widespread phenomenon. The fires release pollutants, which are harmful for human and ecosystem health and alter the Earth's radiative balance. Yet, the impact of various types of BB on the global radiative forcing remains poorly constrained concerning greenhouse gas emissions, BB organic aerosol (OA) chemical composition and related light absorbing properties. Fire emissions composition is influenced by multiple factors (e.g., fuel and thereby vegetation-type, fuel moisture, fire temperature, available oxygen). Due to regional variations in these parameters, studies in different world regions are needed. Here we investigate the influence of seasonally recurring BB on trace gas concentration and air quality at the regional Global Atmosphere Watch (GAW) station Pha Din (PDI) in rural Northwestern Vietnam. PDI is located in a sparsely populated area on the top of a hill (1466 m a.s.l.) and is well suited to study the large-scale fires on the Indochinese Peninsula, whose pollution plumes are frequently transported towards the site [1]. We present continuous trace gas observations of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt;, CO, and O&lt;sub&gt;3&lt;/sub&gt; conducted at PDI since 2014 and interpret the data with atmospheric transport simulations. Annually recurrent large scale BB leads to hourly time-scale peaks CO mixing ratios at PDI of 1000 to 1500 ppb around every April since the start of data collection in 2014. We complement this analysis with carbonaceous PM&lt;sub&gt;2.5 &lt;/sub&gt;chemical composition analyzed during an intensive campaign in March-April 2015. This includes measurements of elemental and organic carbon (EC/OC) and more than 50 organic markers, such as sugars, PAHs, fatty acids and nitro-aromatics [2]. For the intensive campaign, we linked CO, CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and O&lt;sub&gt;3&lt;/sub&gt; mixing ratios to a statistical classification of BB events, which is based on OA composition. We found increased CO and O&lt;sub&gt;3&lt;/sub&gt; levels during medium and high BB influence during the intensive campaign. A backward trajectory analysis confirmed different source regions for the identified periods based on the OA cluster. Typically, cleaner air masses arrived from northeast, i.e., mainland China and Yellow sea during the intensive campaign. The more polluted periods were characterized by trajectories from southwest, with more continental recirculation of the medium cluster, and more westerly advection for the high cluster. These findings highlight that BB activities in Northern Southeast Asia significantly enhances the regional OA loading, chemical PM&lt;sub&gt;2.5 &lt;/sub&gt;composition and the trace gases in northwestern Vietnam. The presented analysis adds valuable data on air quality in a region of scarce data availability.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;REFERENCES&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;[1] Bukowiecki, N. et al. Effect of Large-scale Biomass Burning on Aerosol Optical Properties at the GAW Regional Station Pha Din, Vietnam. AAQR. 19, 1172&amp;#8211;1187 (2019).&lt;/p&gt;&lt;p&gt;[2] Nguyen, D. L, et al. Carbonaceous aerosol composition in air masses influenced by large-scale biomass burning: a case-study in Northwestern Vietnam. ACPD., https://doi.org/10.5194/acp-2020-1027, in review, 2020.&lt;/p&gt;

scholarly journals Sources and processes that control the submicron organic aerosol in an urban Mediterranean environment (Athens) using high temporal resolution chemical composition measurements

2018 ◽  
Author(s):  
Iasonas Stavroulas ◽  
Aikaterini Bougiatioti ◽  
Despina Paraskevopoulou ◽  
Georgios Grivas ◽  
Eleni Liakakou ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Biomass Burning ◽  
Volatile Component ◽  
Organic Aerosol ◽  
Urban Environments ◽  
High Temporal Resolution ◽  
Organic Fraction ◽  
Scanning Mobility Particle Sizer ◽  
Secondary Aerosol ◽  
Combustion Sources

Abstract. Submicron aerosol chemical composition has been studied during a year-long period (26/07/2016–31/07/2017) and two winter-time intensive campaigns (18/12/2013–21/02/2014 and 23/12/2015–17/02/2016), at a central site in Athens, Greece, using an Aerosol Chemical Speciation Monitor (ACSM). Concurrent measurements include a Particle-Into-Liquid Sampler (PILS-IC), a Scanning Mobility Particle Sizer (SMPS), an AE-33 Aethalometer and Ion Chromatography analysis on 24 or 12 hour filter samples. Quality of the ACSM data was assured by comparison versus the above mentioned measurements. The aim of the study was to characterize the seasonal variability of the main fine aerosol constituents and decipher the sources of organic aerosol (OA). Organics were found to contribute almost half of the submicron mass, with concentrations during wintertime reaching up to 200 μg m−3, on occasions. During this season, the primary sources contribute about 34 % of the organic fraction, comprising of biomass burning (10 %), fossil fuel combustion (16 %) and cooking (8 %), while the remaining 66 % is attributed to secondary aerosol. The semi-volatile component of the oxidized organic aerosol (SV-OOA; 31 %) was found to be clearly linked to combustion sources and in particular biomass burning, and even a part of the very oxidized, low-volatility component (LV-OOA; 35 %) could also be attributed to the oxidation of emissions from these primary combustion sources. These results highlight the rising importance of biomass burning in urban environments during wintertime, as revealed through this characteristic example of Athens, Greece, where the economic recessions led to an abrupt shift to biomass burning for heating purposes in winter. During summer, when concentrations of fine aerosols are considerably lower, more than 80 % of the organic fraction is attributed to secondary aerosol (SV-OOA 30 % and LV-OOA 53 %). In contrast to winter, SV-OOA appears to result from a well-mixed type of aerosol, linked to fast photochemical processes and the oxidation of primary traffic and biogenic emissions. Finally, LV-OOA presents a more regional character in summer, owing to the oxidation, within a few days, of organic aerosol.

scholarly journals Optical and Geometrical Properties of Cirrus Clouds in Amazonia Derived From 1-year of Ground-based Lidar Measurements

2016 ◽  
Author(s):  
Diego A. Gouveia ◽  
Boris Barja ◽  
Henrique M. J. Barbosa ◽  
Theotônio Pauliquevis ◽  
Paulo Artaxo
Keyword(s):  
Optical Depth ◽  
Diurnal Cycle ◽  
High Frequency ◽  
Dry Season ◽  
Cirrus Clouds ◽  
Cloud Base ◽  
Wet Season ◽  
Geometrical Properties ◽  
Lidar Ratio ◽  
The Mean

Abstract. For one year, from July 2011 to June 2012, a ground-based raman lidar provided atmospheric observations north of Manaus, Brazil, at an experimental site (2.89° S and 59.97° W) for long-term aerosol and cloud measurements. Upper tropospheric cirrus clouds were observed more frequently than previous reports in tropical regions. The frequency of occurrence was found to be as high as 82 % during the wet season and not lower than 55 % during the dry season. The diurnal cycle shows a minimum around local noon and maximum during late afternoon, associated with the diurnal cycle precipitation. Optical and geometrical characteristics of these cirrus clouds were derived. The mean values were 14.4 ± 2.0 km (top), 12.7 ± 2.3 km (base), 1.7 ± 1.5 km (thickness), and 0.36 ± 1.20 (cloud optical depth). Cirrus clouds were found at temperatures down to –90 °C and 7 % were above the tropopause base. The vertical distribution was not uniform and two cloud types were identified: (1) cloud base > 14 km and optical depth ~0.02, and (2) cloud base < 14 km and optical depth ~0.2. A third type, not previously reported, was identified during the wet season, between 16 and 18 km with optical depth ~0.005. The mean lidar ratio was 20.2 ± 7.0 sr, indicating a mixture of thick plates and long columns. However, the clouds above 14 km have a bimodal distribution during the dry season with a secondary peak at about 40 sr suggesting that thin plates are a major habit. A dependence of the lidar ratio with cloud temperature (altitude) was not found, thus indicating they are well mixed in the vertical. Cirrus clouds classified as subvisible (τ < 0.03) were 40 %, whilst 37.7 % were thin cirrus (0.03 < τ < 0.3) and 22.3 % opaque cirrus (τ > 0.3). Hence, not only does the central Amazon have a high frequency of cirrus clouds, but a large fraction of subvisible cirrus clouds as well. This high frequency of subvisible cirrus clouds may contaminate aerosol optical depth measured by sun-photometers and satellite sensors to an unknown extent.

scholarly journals Biomass-burning and urban emission impacts in the Andes Cordillera region based on in-situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)

2019 ◽  
Author(s):  
Chauvigné Aurélien ◽  
Diego Aliaga ◽  
Marcos Andrade ◽  
Patrick Ginot ◽  
Radovan Krejci ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Particle ◽  
Biomass Burning ◽  
Dry Season ◽  
Wet Season ◽  
Stable Layer ◽  
La Paz ◽  
Extinction Coefficients ◽  
El Alto

Abstract. We present the variability of aerosol particle optical properties measured at the global Atmosphere Watch (GAW) station Chacaltaya (5240 m a.s.l.). The in-situ mountain site is ideally located to study regional impacts of the densely populated urban area of La Paz/El Alto, and the intensive activity in the Amazonian basin. Four year measurements allow to study aerosol particle properties for distinct atmospheric conditions as stable and turbulent layers, different airmass origins, as well as for wet and dry seasons, including biomass-burning influenced periods. The absorption, scattering and extinction coefficients (median annual values of 0.74, 12.14 and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94 and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23 and 14.51 Mm−1 respectively). These parameters also show a pronounced diurnal variation (maximum during daytime, minimum during night-time, as a result of the dynamic and convective effects of leading to lower atmospheric layers reaching the site during daytime. Retrieved intensive optical properties are significantly different from one season to the other, showing the influence of different sources of aerosols according to the season. Both intensive and extensive optical properties of aerosols were found to be different among the different atmospheric layers. The particle light absorption, scattering and extinction coefficients are in average 1.94, 1.49 and 1.55 times higher, respectively, in the turbulent layer compared to the stable layer. We observe that the difference is highest during the wet season and lowest during the dry season. Using wavelength dependence of aerosol particle optical properties, we discriminated contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass-burning and urban transport or industries) emissions according to seasons and tropospheric layers. The main sources influencing measurements at CHC are arising from the urban area of La Paz/El Alto, and regional biomass-burning from the Amazonian basin. Results show a 28 % to 80 % increase of the extinction coefficients during the biomass-burning season with respect to the dry season, which is observed in both tropospheric layers. From this analyse, long-term observations at CHC provides the first direct evidence of the impact of emissions in the Amazonian basin on atmospheric optical properties far away from their sources, all the way to the stable layer.

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