Aerosol chemical composition of the middle Atlas region of North Africa

2021 ◽  
Author(s):  
Nabil Deabji ◽  
Khanneh Wadinga Fomba ◽  
Souad El Hajjaji ◽  
Abdelwahid Mellouki ◽  
Hartmut Herrmann
Keyword(s):  
Boundary Layer ◽  
Organic Matter ◽  
Chemical Composition ◽  
High Altitude ◽  
North Africa ◽  
Atmospheric Composition ◽  
North African ◽  
Air Masses ◽  
Middle Atlas ◽  
Aerosol Chemical Composition

<p>Mountain and high-altitude sites provide representative data for the lower free troposphere and various pathways for aerosol interactions, changing boundary layer heights useful in understanding atmospheric composition. However, few studies exist in African regions despite its diversity in both natural and anthropogenic emissions. For this reason, the ATLAS Mohamed V (AM5) observatory in the Middle Atlas region was established to provide the necessary infrastructure for detailed atmospheric studies in the North African high-altitude region. Here, results of a field study conducted to determine the aerosol chemical composition in this region, understand its variations, and importance in assessing global and regional changes in the atmospheric composition is reported. Particulate matter (PM<sub>10</sub>) filter samples (200) were collected using a high-volume (500l/min) collector in a 12h sampling interval from August to December 2017. The chemical composition of the samples was analyzed for trace metals, ions, elemental carbon, organic carbon, aliphatic hydrocarbons, and polycyclic aromatic hydrocarbon (PAHs) content. The results show that the high-altitude aerosol composition is influenced by regional and transregional transport of different pollutants. Local sources play an important role during periods when the wind speed is low, especially during autumn. Despite the proximity of the site to the Saharan Desert, its influence on the atmospheric composition was mainly seasonal and accounted for only 14% of the sampling duration. The chemical composition was dominated by inorganic elements, mainly suspended dust (47%) and ionic species (16%), and followed by organic matter (15%), water content (12%), and indeterminate mass (9%). Biogenic organics contributed up to 7% of the organic matter with high contributions from compounds such as Nonacosane, Heptacosane, and 2-Pentadecanone. Four main air masses characterized the inflow to the site, which often leads to different aerosol chemical compositions. Mineral dust influenced was seasonal and ranged between 20 and 70% of the PM mass with peaks observed during the summer and was accompanied by high concentrations of SO<sub>4</sub><sup>2-</sup> of up to 1.3 µg/m³. PM<sub>10</sub> concentrations during winter were low (< 30 µg/m³), with a dominance of marine air masses (53%) carrying aerosols rich in sea salt and polluted anthropogenic aerosols from the coastal regions (Rabat and Casablanca). During the day-time, mineral dust contribution to PM increased by about 42% due to road dust resuspension. In contrast, during night-time, an increase in the concentrations of PAHs, ketones, and anthropogenic metals such as Pb, Ni, and Cu was found due to variations in the boundary layer height. The results provide first insights into typical North African high-altitude background aerosol chemical composition useful for long-term assessment of climate and regional influence of air pollution in North Africa.</p><p> </p>

scholarly journals First insights into northern Africa high-altitude background aerosol chemical composition and source influences

2021 ◽  
Vol 21 (24) ◽  
pp. 18147-18174
Author(s):  
Nabil Deabji ◽  
Khanneh Wadinga Fomba ◽  
Souad El Hajjaji ◽  
Abdelwahid Mellouki ◽  
Laurent Poulain ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
High Altitude ◽  
North Africa ◽  
Mineral Dust ◽  
Water Soluble ◽  
Atmospheric Composition ◽  
Chemical Compositions ◽  
Aerosol Composition ◽  
Aerosol Chemical Composition

Abstract. Field measurements were conducted to determine aerosol chemical composition at a newly established remote high-altitude site in North Africa at the Atlas Mohammed V (AMV) atmospheric observatory located in the Middle Atlas Mountains. The main objectives of the present work are to investigate the variations in the aerosol composition and better assess global and regional changes in atmospheric composition in North Africa. A total of 200 particulate matter (PM10) filter samples were collected at the site using a high-volume (HV) collector in a 12 h sampling interval from August to December 2017. The chemical composition of the samples was analyzed for trace metals, water-soluble ions, organic carbon (OC/EC), aliphatic hydrocarbons, and polycyclic aromatic hydrocarbon (PAH) contents. The results indicate that high-altitude aerosol composition is influenced by both regional and transregional transport of emissions. However, local sources play an important role, especially during low wind speed periods, as observed for November and December. During background conditions characterized by low wind speeds (avg. 3 m s-1) and mass concentrations in the range from 9.8 to 12 μg m-3, the chemical composition is found to be dominated by inorganic elements, mainly suspended dust (61 %) and ionic species (7 %), followed by organic matter (7 %), water content (12 %), and unidentified mass (11 %). Despite the proximity of the site to the Sahara, its influence on the atmospheric composition at this high-altitude site was mainly seasonal and accounted for only 22 % of the sampling duration. Biogenic organics contributed up to 7 % of the organic matter with high contributions from compounds such as heneicosane, hentriacontane, and nonacosane. The AMV site is dominated by four main air mass inflows, which often leads to different aerosol chemical compositions. Mineral dust influence was seasonal and ranged between 21 % and 74 % of the PM mass, with peaks observed during the summer, and was accompanied by high concentrations of SO42- of up to 3.0 μg m-3. During winter, PM10 concentrations are low (<30 μg m-3), the influence of the desert is weaker, and the marine air masses (64 %) are more dominant with a mixture of sea salt and polluted aerosol from the coastal regions (Rabat and Casablanca). During the daytime, mineral dust contribution to PM increased by about 42 % because of road dust resuspension. In contrast, during nighttime, an increase in the concentrations of alkanes, PAHs, alkane-2-ones, and anthropogenic metals such as Pb, Ni, and Cu was found due to variations in the boundary layer height. The results provide the first detailed seasonal and diurnal variation of the aerosol chemical composition, which is valuable for long-term assessment of climate and regional influence of air pollution in North Africa.

scholarly journals First insights into Northern Africa high-altitude background aerosol chemical composition and source influences

2021 ◽  
Author(s):  
Nabil Deabji ◽  
Khanneh Wadinga Fomba ◽  
Souad El Hajjaji ◽  
Abdelwahid Mellouki ◽  
Hartmut Herrmann
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
High Altitude ◽  
Field Measurements ◽  
High Volume ◽  
Ionic Species ◽  
Atmospheric Composition ◽  
Chemical Compositions ◽  
Aerosol Composition ◽  
Aerosol Chemical Composition

Abstract. Field measurements were conducted to determine aerosol chemical composition in a newly established remote high-altitude site in North Africa to investigate the variations in aerosol composition useful in assessing global and regional changes in atmospheric composition. Particulate matter (PM10) filter samples (200) were collected at the Atlas Mohammed V atmospheric observatory (AM5) located in the Middle-Atlas Mountains in Morocco using a high-volume (HV) collector in a 12 h sampling interval from August to December 2017. The chemical composition of the samples was analyzed for trace metals, ions, elemental carbon, organic carbon, aliphatic hydrocarbons, and polycyclic aromatic hydrocarbon (PAHs) content. The results indicate that high-altitudes aerosol composition is influenced by both regional as well as trans-regional transport of emissions. However, local sources play an important role, especially during low wind speed periods, as observed for November and December. Despite the proximity of the site to the Sahara Desert, its influence on the atmospheric composition at this high-altitude site was mainly seasonal and accounted for only 14 % of the sampling duration. Background conditions at this remote site are characterized by low wind speeds (Av. 2.5 m/s) and mass concentrations in the range of 9.8 and 20 µg/m3. The chemical composition is found to be dominated by inorganic elements, mainly suspended dust (47 %) and ionic species (16 %), followed by organic matter (15 %), water content (12 %), and indeterminate mass (9 %). Biogenic organics contributed up to 7 % of the organic matter with high contributions from compounds such as Nonacosane, Heptacosane, and 2-Pentadecanone. The AM5 site is dominated by four main air mass inflow, which often leads to different aerosol chemical compositions. Mineral dust influenced was seasonal and ranged between 20 and 70 % of the PM mass with peaks observed during the summer and was accompanied by high concentrations of SO42− of up to 1.3 µg/m3. During winter, PM10 concentrations are low (

scholarly journals Identifying source regions of air masses sampled at the tropical high-altitude site of Chacaltaya using WRF-FLEXPART and cluster analysis

2021 ◽  
Author(s):  
Diego Aliaga ◽  
Victoria A. Sinclair ◽  
Marcos Andrade ◽  
Paulo Artaxo ◽  
Samara Carbone ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Altitude ◽  
Long Range ◽  
Diurnal Cycle ◽  
Observation Time ◽  
Particle Nucleation ◽  
Free Troposphere ◽  
Air Mass ◽  
Air Masses ◽  
Source Regions

Abstract. Observations of aerosol and trace gases in the remote troposphere are vital to quantify background concentrations and identify long term trends in atmospheric composition on large spatial scales. Measurements made at high altitude are often used to study free tropospheric air however such high-altitude sites can be influenced by boundary layer air masses. Thus, accurate information on air mass origin and transport pathways to high altitude sites is required. Here we present a new method, based on the source-receptor relationship (SRR) obtained from backwards WRF-FLEXPART simulations and a k-means clustering approach, to identify source regions of air masses arriving at measurement sites. Our method is tailored to areas of complex terrain and to stations influenced by both local and long-range sources. We have applied this method to the Chacaltaya (CHC) GAW station (5240 m a.s.l.,16.35° S, 68.13° W) for the 6-month duration of the “Southern hemisphere high altitude experiment on particle nucleation and growth” (SALTENA) to identify where sampled air masses originate and to quantify the influence of the boundary layer and the free troposphere. A key aspect of our method is that it is probabilistic and for each observation time, more than one air mass (cluster) can influence the station and the percentage influence of each air mass can be quantified. This is in contrast to binary methods, which label each observation time as influenced either by boundary layer or free troposphere air masses. We find that on average, 9% of the air sampled at CHC, at any given observation time, has been in contact with the surface within 4 days prior to arriving at CHC, 24% of the air was located below 1.5 km above ground level and consequently, 76% of the measured air masses at CHC represent free tropospheric air. However, pure free-tropospheric influences are rare and often samples are concurrently influenced by both boundary-layer and free-tropospheric air masses. A clear diurnal cycle is present with very few air masses that have been in contact with the surface being detected at night. The 6-month analysis also shows that the most dominant air mass (cluster) originates in the Amazon and is responsible for 29% of the sampled air. Furthermore, short-range clusters (origins within 100 km of CHC) have high temporal frequency modulated by local meteorology driven by the diurnal cycle whereas the mid- and long-range clusters’ (>200 km) variability occurs on timescales governed by synoptic-scale dynamics. To verify the reliability of our method, in-situ sulfate observations from CHC are combined with the SRR clusters to correctly identify the (pre-known) source of the sulfate: the Sabancaya volcano located 400 km northwest from the station.

scholarly journals Vertical distribution of sub-micron aerosol chemical composition from North-Western Europe and the North-East Atlantic

2009 ◽  
Vol 9 (2) ◽  
pp. 9117-9150
Author(s):  
W. T. Morgan ◽  
J. D. Allan ◽  
K. N. Bower ◽  
G. Capes ◽  
J. Crosier ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
Vertical Distribution ◽  
Western Europe ◽  
Vertical Profiles ◽  
East Atlantic ◽  
Air Masses ◽  
North East ◽  
The North ◽  
The Vertical Distribution

Abstract. A synthesis of UK based airborne in-situ measurements of aerosol properties representing air masses from North-West Europe and the North-East Atlantic is presented. The major focus of the study is the vertical distribution of sub-micron aerosol chemical composition. Vertical profiles are derived from a Quadrupole Aerosol Mass Spectrometer (Q-AMS). Background sub-micron aerosol vertical profiles are identified and are primarily composed of organic matter and sulphate aerosol. Such background conditions occurred predominantly during periods associated with long-range air mass transport across the Atlantic. These instances may serve as useful model input of aerosol to Western Europe. Increased mass concentration episodes are coincident with European outflow and periods of stagnant/recirculating air masses. Such periods are characterised by significantly enhanced concentrations of nitrate aerosol relative to those of organic matter and sulphate. Periods of enhanced ground level PM2.5 loadings are coincident with instances of high nitrate mass fractions measured on-board the aircraft, indicating that nitrate is a significant contributor to regional pollution episodes. The vertical structure of the sulphate and organic aerosol profiles were shown to be primarily driven by large-scale dynamical processes. The vertical distribution of nitrate is likely determined by both dynamic and thermodynamic processes, with chemical partitioning of gas phase precursors to the particle phase occurring at lower temperatures at the top of the boundary layer. Such effects have profound implications for the aerosol's lifetime and subsequent impacts, highlighting the requirement for accurate representation of the aerosol vertical distribution.

scholarly journals Chemical composition of tropospheric air masses encountered during high altitude flights (>11.5 km) during the 2009 fall Operation Ice Bridge field campaign

2012 ◽  
Vol 117 (D17) ◽  
pp. n/a-n/a ◽  
Author(s):  
Mei Ying Melissa Yang ◽  
Stephanie A. Vay ◽  
Andreas Stohl ◽  
Yonghoon Choi ◽  
Glenn S. Diskin ◽  
...  
Keyword(s):  
Chemical Composition ◽  
High Altitude ◽  
Field Campaign ◽  
Air Masses

Relationships among aerosol water soluble organic matter, iron and aluminum in European, North African, and Marine air masses from the 2010 US GEOTRACES cruise

2013 ◽  
Vol 154 ◽  
pp. 24-33 ◽  
Author(s):  
Andrew S. Wozniak ◽  
Rachel U. Shelley ◽  
Rachel L. Sleighter ◽  
Hussain A.N. Abdulla ◽  
Peter L. Morton ◽  
...  
Keyword(s):  
Organic Matter ◽  
Water Soluble ◽  
Soluble Organic Matter ◽  
North African ◽  
Air Masses ◽  
European North ◽  
Marine Air

scholarly journals Chemical composition of PM<sub>10</sub> and PM<sub>1</sub> at the high-altitude Himalayan station Nepal Climate Observatory-Pyramid (NCO-P) (5079 m a.s.l.)

2009 ◽  
Vol 9 (6) ◽  
pp. 25487-25522 ◽  
Author(s):  
S. Decesari ◽  
M. C. Facchini ◽  
C. Carbone ◽  
L. Giulianelli ◽  
M. Rinaldi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
High Altitude ◽  
Seasonal Cycle ◽  
Mineral Dust ◽  
Monsoon Season ◽  
Optically Active ◽  
Moist Convection ◽  
Anthropogenic Aerosols ◽  
High Himalayas

Abstract. We report chemical composition data for PM10 and PM1 from the Nepal Climate Observatory-Pyramid (NCO-P), the world's highest aerosol observatory, located at 5079 m a.s.l. at the foothills of Mt. Everest. Despite its high altitude, the average PM10 mass apportioned by the chemical analyses is of the order of 6 μg m−3 (i.e., 10 μg/scm), with almost a half of this mass accounted for by organic matter, elemental carbon (EC) and inorganic ions, the rest being mineral dust. Organic matter, in particular, accounted for by 2.0 μg m−3 (i.e., 3.6 μg/scm) on a yearly basis, and it is by far the major PM10 component beside mineral oxides. Non-negligible concentrations of EC were also observed (0.36 μg/scm), confirming that optically-active aerosol produced from combustion sources can be efficiently transported up the altitudes of Himalayan glaciers. The concentrations of carbonaceous and ionic aerosols follow a common time trend with a maximum in the premonsoon season, a minimum during the monsoon and a slow "ramp-up" period in the postmonsoon and dry seasons, which is the same phenomenology observed for other Nepalese Himalayan sites in previous studies. Such seasonal cycle can be explained by the seasonal variations of dry and moist convection and of wet scavenging processes characterizing the climate of north Indian subcontinent. We document the effect of orographic transport of carbonaceous and sulphate particles upslope the Himalayas, showing that the valley breeze circulation, which is almost permanently active during the out-of-monsoon season, greatly impacts the chemical composition of PM10 and PM1 in the high Himalayas and provides an efficient mechanism for bringing anthropogenic optically-active aerosols into the Asian upper troposphere (>5000 m a.s.l.). The concentrations of mineral dust are impacted to a smaller extent by valley breezes and follow a unique seasonal cycle which suggest multiple source areas in central and south-west Asia. Our findings, based on two years of observations of the aerosol chemical composition, provide clear evidence that the southern side of the high Himalayas are impacted by transport of anthropogenic aerosols which constitute the Asian brown cloud.

scholarly journals Chemical composition and source attribution of sub-micrometre aerosol particles in the summertime Arctic lower troposphere

2021 ◽  
Vol 21 (8) ◽  
pp. 6509-6539
Author(s):  
Franziska Köllner ◽  
Johannes Schneider ◽  
Megan D. Willis ◽  
Hannes Schulz ◽  
Daniel Kunkel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Organic Matter ◽  
Chemical Composition ◽  
Dicarboxylic Acids ◽  
The Arctic ◽  
Source Attribution ◽  
Arctic Boundary Layer ◽  
Air Mass ◽  
Particle Composition ◽  
Aerosol Mass

Abstract. Aerosol particles impact the Arctic climate system both directly and indirectly by modifying cloud properties, yet our understanding of their vertical distribution, chemical composition, mixing state, and sources in the summertime Arctic is incomplete. In situ vertical observations of particle properties in the high Arctic combined with modelling analysis on source attribution are in short supply, particularly during summer. We thus use airborne measurements of aerosol particle composition to demonstrate the strong contrast between particle sources and composition within and above the summertime Arctic boundary layer. In situ measurements from two complementary aerosol mass spectrometers, the Aircraft-based Laser Ablation Aerosol Mass Spectrometer (ALABAMA) and an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), are presented alongside black carbon measurements from an single particle soot photometer (SP2). Particle composition analysis was complemented by trace gas measurements, satellite data, and air mass history modelling to attribute particle properties to particle origin and air mass source regions. Particle composition above the summertime Arctic boundary layer was dominated by chemically aged particles, containing elemental carbon, nitrate, ammonium, sulfate, and organic matter. From our analysis, we conclude that the presence of these particles was driven by transport of aerosol and precursor gases from mid-latitudes to Arctic regions. Specifically, elevated concentrations of nitrate, ammonium, and organic matter coincided with time spent over vegetation fires in northern Canada. In parallel, those particles were largely present in high CO environments (> 90 ppbv). Additionally, we observed that the organic-to-sulfate ratio was enhanced with increasing influence from these fires. Besides vegetation fires, particle sources in mid-latitudes further include anthropogenic emissions in Europe, North America, and East Asia. The presence of particles in the Arctic lower free troposphere, particularly sulfate, correlated with time spent over populated and industrial areas in these regions. Further, the size distribution of free tropospheric particles containing elemental carbon and nitrate was shifted to larger diameters compared to particles present within the boundary layer. Moreover, our analysis suggests that organic matter, when present in the Arctic free troposphere, can partly be identified as low molecular weight dicarboxylic acids (oxalic, malonic, and succinic acid). Particles containing dicarboxylic acids were largely present when the residence time of air masses outside Arctic regions was high. In contrast, particle composition within the marine boundary layer was largely driven by Arctic regional processes. Air mass history modelling demonstrated that alongside primary sea spray particles, marine biogenic sources contributed to secondary aerosol formation via trimethylamine, methanesulfonic acid, sulfate, and other organic species. Our findings improve our knowledge of mid-latitude and Arctic regional sources that influence the vertical distribution of particle chemical composition and mixing state in the Arctic summer.

scholarly journals Influence of aerosol chemical composition on N<sub>2</sub>O<sub>5</sub> uptake: airborne regional measurements in North-Western Europe

2014 ◽  
Vol 14 (13) ◽  
pp. 19673-19718 ◽  
Author(s):  
W. T. Morgan ◽  
B. Ouyang ◽  
J. D. Allan ◽  
E. Aruffo ◽  
P. Di Carlo ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Ammonium Nitrate ◽  
Water Content ◽  
Atmospheric Chemistry ◽  
Western Europe ◽  
Organic Aerosol ◽  
Atmospheric Composition ◽  
Airborne Measurements ◽  
North Western ◽  
Aerosol Chemical Composition

Abstract. Aerosol chemical composition was found to influence nighttime atmospheric chemistry during a series of airborne measurements in North-Western Europe in summer conditions, which has implications for regional air quality and climate. The uptake of dinitrogen pentoxide, γ (N2O5), to particle surfaces was found to be modulated by the amount of water content and ammonium nitrate present in the aerosol. The conditions prevalent in this study suggest that the net uptake rate of N2O5 to atmospheric aerosols was relatively efficient compared to previous studies, with γ (N2O5) values in the range 0.01–0.03. This is likely a consequence of the elevated relative humidity in the region, which promotes greater aerosol water content. Increased nitrate concentrations relative to particulate water were found to suppress N2O5 uptake. The results presented here contrast with previous ambient studies of N2O5 uptake, which have generally taken place in low-nitrate environments in the USA. Comparison of the N2O5 uptake derived from the measurements with a parameterised scheme that is based on the ratio of particulate water to nitrate yielded reasonably good agreement in terms of the magnitude and variation in uptake, provided the effect of chloride was neglected. An additional suppression of the parameterised uptake is likely required to fully capture the variation in N2O5 uptake, which could be achieved via the known suppression by organic aerosol. However, existing parameterisations representing the suppression by organic aerosol were unable to fully represent the variation in N2O5 uptake. These results provide important ambient measurement constraint on our ability to predict N2O5 uptake in regional and global aerosol models. N2O5 uptake is a potentially important source of nitrate aerosol and a sink of the nitrate radical, which is the main nocturnal oxidant in the atmosphere. The results further highlight the importance of ammonium nitrate in North-Western Europe as a key component of atmospheric composition in the region.

scholarly journals Vertical distribution of sub-micron aerosol chemical composition from North-Western Europe and the North-East Atlantic

2009 ◽  
Vol 9 (15) ◽  
pp. 5389-5401 ◽  
Author(s):  
W. T. Morgan ◽  
J. D. Allan ◽  
K. N. Bower ◽  
G. Capes ◽  
J. Crosier ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
Vertical Distribution ◽  
Western Europe ◽  
Vertical Profiles ◽  
East Atlantic ◽  
Air Masses ◽  
North East ◽  
The North ◽  
The Vertical Distribution

Abstract. A synthesis of UK based airborne in-situ measurements of aerosol properties representing air masses from North-West Europe and the North-East Atlantic is presented. The major focus of the study is the vertical distribution of sub-micron aerosol chemical composition. Vertical profiles are derived from a Quadrupole Aerosol Mass Spectrometer (Q-AMS). Background sub-micron aerosol vertical profiles are identified and are primarily composed of organic matter and sulphate aerosol. Such background conditions occurred predominantly during periods associated with long-range air mass transport across the Atlantic. These instances may serve as useful model input of aerosol to Western Europe. Increased mass concentration episodes are coincident with European outflow and periods of stagnant/recirculating air masses. Such periods are characterised by significantly enhanced concentrations of nitrate aerosol relative to those of organic matter and sulphate. Periods of enhanced ground level PM2.5 loadings are coincident with instances of high nitrate mass fractions measured on-board the aircraft, indicating that nitrate is a significant contributor to regional pollution episodes. The vertical structure of the sulphate and organic aerosol profiles were shown to be primarily driven by large-scale dynamical processes. The vertical distribution of nitrate is likely determined by both dynamic and thermodynamic processes, with chemical partitioning of gas phase precursors to the particle phase occurring at lower temperatures at the top of the boundary layer. Such effects have profound implications for the aerosol's lifetime and subsequent impacts, highlighting the requirement for accurate representation of the aerosol vertical distribution.

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