Browsing by Autor "Claudia Mohr"

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Comment on egusphere-2023-1298
(2023) Isabel Moreno; Radovan Krejčí; Jean‐Luc Jaffrezo; Gaëlle Uzu; Andrés Alástuey; Marcos Andrade; Valeria Mardóñez; Alkuin Maximilian Koenig; Diego Aliaga; Claudia Mohr
Abstract. The chemical composition of PM10 and PM2.5 was studied at the summit of Mt. Chacaltaya (5380 masl, lat.-16.346950º, lon. -68.128250º) providing a unique long-term record spanning from December 2011 to March 2020. The chemical composition of aerosol at the Chacaltaya GAW site is representative of the regional background, seasonally affected by biomass burning practices and by nearby anthropogenic emissions from the metropolitan area of La Paz – El Alto. Concentration levels are clearly influenced by seasons with minimum occurring during the wet season (December to March) and maxima occurring during the dry and transition seasons (April to November). Ions, total carbon (EC+OC) and saccharide concentrations range between 558–1785, 384–1120 and 4.3–25.5 ng m-3 for bulk PM10 and 917–2308, 519–1175 and 3.9–24.1 ng m-3 for PM2.5, respectively. Such concentrations are overall lower compared to other high-altitude stations around the globe, but higher than Amazonian remote sites (except for OC). For PM10, there is dominance of insoluble mineral matter (33–56 % of the mass), organic matter (7–34 %) and secondary inorganic aerosol (15–26 %). Chemical composition profiles were identified for different origins: EC, NO3-, NH4+, glucose, C2O4-2 for the nearby urban and rural areas; OC, EC, NO3-, K+, acetate, formiate, levoglucosan, some F- and Br- for biomass burning; MeSO3-, Na+, Mg2+, Br- for aged marine emissions from the Pacific Ocean; arabitol, mannitol, K+ for biogenic emissions; Na+, Ca2+, Mg2+ for soil dust, and SO42-, F-, and some Cl- for volcanism. Regional biomass-burning practices influence the soluble fraction of the aerosol particularly between July and September. The organic fraction is present all year round and has both anthropogenic (biomass burning and other combustion sources) and natural (primary and secondary biogenic emissions) origins, with the OC/EC mass ratio being practically constant all year round (10.5±38.9). Peruvian volcanism dominates the SO42- concentration since 2014, though it presents a strong temporal variability due to the intermittence of the sources and seasonal changes on the transport patterns. These measurements represent some of the first long-term observations of aerosol chemical composition at a continental high-altitude site in the tropical Southern hemisphere.
Comment on egusphere-2023-1298
(2023) Isabel Moreno; Radovan Krejčí; Jean‐Luc Jaffrezo; Gaëlle Uzu; Andrés Alástuey; Marcos Andrade; Valeria Mardóñez; Alkuin Maximilian Koenig; Diego Aliaga; Claudia Mohr
Abstract. The chemical composition of PM10 and PM2.5 was studied at the summit of Mt. Chacaltaya (5380 masl, lat.-16.346950º, lon. -68.128250º) providing a unique long-term record spanning from December 2011 to March 2020. The chemical composition of aerosol at the Chacaltaya GAW site is representative of the regional background, seasonally affected by biomass burning practices and by nearby anthropogenic emissions from the metropolitan area of La Paz – El Alto. Concentration levels are clearly influenced by seasons with minimum occurring during the wet season (December to March) and maxima occurring during the dry and transition seasons (April to November). Ions, total carbon (EC+OC) and saccharide concentrations range between 558–1785, 384–1120 and 4.3–25.5 ng m-3 for bulk PM10 and 917–2308, 519–1175 and 3.9–24.1 ng m-3 for PM2.5, respectively. Such concentrations are overall lower compared to other high-altitude stations around the globe, but higher than Amazonian remote sites (except for OC). For PM10, there is dominance of insoluble mineral matter (33–56 % of the mass), organic matter (7–34 %) and secondary inorganic aerosol (15–26 %). Chemical composition profiles were identified for different origins: EC, NO3-, NH4+, glucose, C2O4-2 for the nearby urban and rural areas; OC, EC, NO3-, K+, acetate, formiate, levoglucosan, some F- and Br- for biomass burning; MeSO3-, Na+, Mg2+, Br- for aged marine emissions from the Pacific Ocean; arabitol, mannitol, K+ for biogenic emissions; Na+, Ca2+, Mg2+ for soil dust, and SO42-, F-, and some Cl- for volcanism. Regional biomass-burning practices influence the soluble fraction of the aerosol particularly between July and September. The organic fraction is present all year round and has both anthropogenic (biomass burning and other combustion sources) and natural (primary and secondary biogenic emissions) origins, with the OC/EC mass ratio being practically constant all year round (10.5±38.9). Peruvian volcanism dominates the SO42- concentration since 2014, though it presents a strong temporal variability due to the intermittence of the sources and seasonal changes on the transport patterns. These measurements represent some of the first long-term observations of aerosol chemical composition at a continental high-altitude site in the tropical Southern hemisphere.
Direct high-altitude observations of 2-methyltetrols in the gas- and particle phase in air masses from Amazonia
(Royal Society of Chemistry, 2025) Claudia Mohr; Joel A. Thornton; Manish Shrivastava; Anouck Chassaing; Ilona Riipinen; Federico Bianchi; Marcos Andrade; Cheng Wu
We present direct observations of 2-methyltetrol (C5H12O4) in the gas- and particle phase from the deployment of a Filter Inlet for Gases and Aerosols coupled to a Time-of-Flight Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) during the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA), which took place between December 2017 and June 2018 at the high-altitude Global Atmosphere Watch station Chacaltaya (CHC) located at 5240 m a s l in the Bolivian Andes. 2-Methyltetrol signals were dominant in a factor resulting from Positive Matrix Factorization (PMF) identified as influenced by Amazon emissions. We combine these observations with investigations of isoprene oxidation chemistry and uptake in an isolated deep convective cloud in the Amazon using a photochemical box model with coupled cloud microphysics and show that, likely, 2-methyltetrol is taken up by hydrometeors or formed in situ in the convective cloud, and then transported in the particle phase in the cold environment of the Amazon outflow and to the station, where it partially evaporates.
Molecular characterization and volatility of organonitrates: Latest observations from field and laboratory
(2020) Claudia Mohr; Cheng Wu; Huang Wei; Emelie Graham; Federico Bianchi; Marcos Andrade; David M. Bell
&lt;p&gt;Here we show recent results from different field and laboratory campaigns focusing on organonitrate (ON) formation, mass concentration, and physicochemical properties such as volatility. ONs are formed via volatile organic compounds (VOC) and NO&lt;sub&gt;x&lt;/sub&gt;. They are therefore key species for our understanding of the interaction between the biosphere and anthropogenic activities, and the effects of altering both VOC and NO&lt;sub&gt;x&lt;/sub&gt; emissions due to climate change and/or air quality mitigation measures. Recently, we were able to show that ONs from different precursor VOC can also contribute significantly to the growth of newly formed particles in the atmosphere to sizes where they can become active and cloud condensation nuclei (Huang et al., 2019).&lt;/p&gt;&lt;p&gt;We present direct, real-time observations of ONs in the gas and particle phase at the highest atmospheric research station in the world, Chacaltaya (5240 m a. s. l) in Bolivia. This southern hemisphere station is often located in the free troposphere during night time, and influenced by the emissions from the nearby El Alto-La Paz metropolitan area, and biogenic emissions from surrounding forests as well as from the Amazon through long-range transport. ONs were measured using a Chemical Ionization Mass Spectrometer with a Filter Inlet for Gases and Aerosols. We observed hundreds of highly functionalized ONs with different molecular composition during day- and nighttime, indicating different sources and formation processes. A large contribution of the highly functionalized ONs was found especially during new particle formation events regularly observed at this location (Rose et al., 2015). Observations from the field will be compared to results from the Nitrate Aerosol and Volatility Experiment (NArVE) at the EUROCHAMP 2020 PACS-C3 smog chamber (PSI, Switzerland), where we investigated the ON fraction, chemical composition, and volatility of secondary organic aerosol (SOA) formed via nitrate radical initiated oxidation reactions of biogenic and anthropogenic VOC.&lt;/p&gt;
Polychlorinated Alkane Profiles and Concentrations in Bolivian Andes Soils Point to a Long-Range Transport Influence
(American Chemical Society, 2026) Bo Yuan; Cheng Wu; Cynthia A. de Wit; Claudia Mohr; Marcos Andrade; Isabel Moreno; Volker Brüchert; Rienk H. Smittenberg; Matthew MacLeod
High-altitude terrain may intersect the upper atmospheric boundary layer and exhibit distinct environmental dynamics. We investigated the anthropogenic pollutants polychlorinated alkanes (PCAs, also known as chlorinated paraffins) in surface soils along a transect from the La Paz-El Alto metropolitan area in Bolivia (3200-4100 masl) to the upper slopes of Mount Chacaltaya (>5200 masl), around 16 km away. Concentrations of PCAs in urban soils (750-5,230 ng/g organic carbon [OC]) decreased exponentially with increasing distance from the urban boundary, declining to ∼150 ng/g OC at elevations below 4,700 masl. Beyond 4,700 masl concentrations increased again, reaching levels comparable to those in the urban area, 1,670-4,300 ng/g OC, above 5,000 masl. Given that pollutant concentrations typically decline with distance from their source, this altitudinal trend, together with a pronounced shift in PCA forensic fingerprints near 4,700 masl, strongly suggests contributions from sources beyond the local metropolitan area. Carbon and nitrogen isotope signatures in organic carbon further support long-range transport as a source, consistent with previous modeling and observations that the upper slopes of Mount Chacaltaya predominantly receive air masses and organic carbon from distant regions via transport in the free troposphere. Our observation that pollutant levels in high-altitude areas are comparable to those in the metropolis of 1.8-million inhabitants underscores the efficiency of long-range atmospheric transport.
Source region cluster analysis in the high-altitude measuring site of Chacaltaya with WRF and FLEXPART
(2020) Diego Aliaga; Victoria A. Sinclair; Qiaozhi Zha; Marcos Andrade; Claudia Mohr; Radovan Krejčí
&lt;p&gt;Measuring aerosol at high altitude sites is useful as it enables sampling of the free troposphere over long time frames. However, in order to draw conclusions from station measurement data, we need to determine which air mass sources are present at any given sampling time. This task is challenging at mountain sites, due to complex topography which in turn drives complex meteorology. Between December 2017 and May 2018, the Southern hemisphere high ALTitude Experiment on particle Nucleation And growth (SALTENA) campaign was conducted at Chacaltaya in Bolivia at 5240 m a.s.l. The data set obtained in this campaign contains records of nearly all relevant aerosol characteristics and aerosol precursors. To identify the source regions of the observed air masses we performed high resolution (down to 1 km) simulations with the Weather Research and Forecasting Model (WRF). The WRF model output is then used to as input to the Lagrangian particle dispersion model (FLEXPART). FLEXPART simulations are initialised every hour and 20 thousand particles are released per hour and track backwards in time for 96 hours. The FLEXPART footprint output is regridded onto a log-polar cylindrical grid where we perform a &amp;#8216;K-means&amp;#8217; cluster analysis on the 3D cells defined by the grid. The cells are clustered based on the time series of their source receptor relationship (i.e. emission sensitivities), producing regions (clusters) resolved not only in the horizontal but also the vertical domain. Our results show that regions located close to the station (&lt;100km) have a low but persistent influence with diurnal variations and close contact to the surface. Mid-range regions (100-800km) have the highest influence with a higher percentage of air masses from the free troposphere. Long-range regions (&gt;800km) have a higher influence than the short-range regions but lower than the middle-range regions. Most of the air masses from these long-range regions come from the free troposphere. With this method we have successfully resolved the various air mass influences at the measurement site. The high meteorological resolution and the stochastic nature of FLEXPART are seminal for capturing the transport pathways.&lt;/p&gt;
Tropical tropospheric aerosol sources and chemical composition observed at high altitude in the Bolivian Andes
(Copernicus Publications, 2024) Isabel Moreno; Radovan Krejčí; Jean‐Luc Jaffrezo; Gaëlle Uzu; Andrés Alástuey; Marcos Andrade; Valeria Mardóñez; Alkuin Maximilian Koenig; Diego Aliaga; Claudia Mohr
Abstract. The chemical composition of PM10 and non-overlapping PM2.5 was studied at the summit of Mt. Chacaltaya (5380 m a.s.l., lat. −16.346950°, long. −68.128250°) providing a unique long-term record spanning from December 2011 to March 2020. The chemical composition of aerosol at the Chacaltaya Global Atmosphere Watch (GAW) site is representative of the regional background, seasonally affected by biomass burning practices and by nearby anthropogenic emissions from the metropolitan area of La Paz–El Alto. Concentration levels are clearly influenced by seasons with minima occurring during the wet season (December to March) and maxima occurring during the dry and transition seasons (April to November). Ions, total carbon (EC + OC), and saccharide interquartile ranges for concentrations are 558–1785, 384–1120, and 4.3–25.5 ng m−3 for bulk PM10 and 917–2308, 519–1175, and 3.9–24.1 ng m−3 for PM2.5, respectively, with most of the aerosol seemingly present in the PM2.5 fraction. Such concentrations are overall lower compared to other high-altitude stations around the globe but higher than Amazonian remote sites (except for OC). For PM10, there is dominance of insoluble mineral matter (33 %–56 % of the mass), organic matter (7 %–34 %), and secondary inorganic aerosol (15 %–26 %). Chemical composition profiles were identified for different origins: EC, NO3-, NH4+, glucose, and C2O42- for the nearby urban and rural areas; OC, EC, NO3-, K+, acetate, formate, levoglucosan, and some F− and Br− for biomass burning; MeSO3-, Na+, Mg2+, K+, and Ca2+ for aged marine emissions from the Pacific Ocean; arabitol, mannitol, and glucose for biogenic emissions; Na+, Ca2+, Mg2+, and K+ for soil dust; and SO42-, F−, and some Cl− for volcanism. Regional biomass burning practices influence the soluble fraction of the aerosol between June and November. The organic fraction is present all year round and has both anthropogenic (biomass burning and other combustion sources) and natural (primary and secondary biogenic emissions) origins, with the OC/EC mass ratio being practically constant all year round (10.5 ± 5.7, IQR 8.1–13.3). Peruvian volcanism has dominated the SO42- concentration since 2014, though it presents strong temporal variability due to the intermittence of the sources and seasonal changes in the transport patterns. These measurements represent some of the first long-term observations of aerosol chemical composition at a continental high-altitude site in the tropical Southern Hemisphere.
Tropical tropospheric aerosol sources and chemical composition observed at high-altitude in the Bolivian Andes
(2023) Isabel Moreno; Radovan Krejčí; Jean‐Luc Jaffrezo; Gaëlle Uzu; Andrés Alástuey; Marcos Andrade; Valeria Mardóñez; Alkuin Maximilian Koenig; Diego Aliaga; Claudia Mohr
Abstract. The chemical composition of PM10 and PM2.5 was studied at the summit of Mt. Chacaltaya (5380 masl, lat.-16.346950º, lon. -68.128250º) providing a unique long-term record spanning from December 2011 to March 2020. The chemical composition of aerosol at the Chacaltaya GAW site is representative of the regional background, seasonally affected by biomass burning practices and by nearby anthropogenic emissions from the metropolitan area of La Paz – El Alto. Concentration levels are clearly influenced by seasons with minimum occurring during the wet season (December to March) and maxima occurring during the dry and transition seasons (April to November). Ions, total carbon (EC+OC) and saccharide concentrations range between 558–1785, 384–1120 and 4.3–25.5 ng m-3 for bulk PM10 and 917–2308, 519–1175 and 3.9–24.1 ng m-3 for PM2.5, respectively. Such concentrations are overall lower compared to other high-altitude stations around the globe, but higher than Amazonian remote sites (except for OC). For PM10, there is dominance of insoluble mineral matter (33–56 % of the mass), organic matter (7–34 %) and secondary inorganic aerosol (15–26 %). Chemical composition profiles were identified for different origins: EC, NO3-, NH4+, glucose, C2O4-2 for the nearby urban and rural areas; OC, EC, NO3-, K+, acetate, formiate, levoglucosan, some F- and Br- for biomass burning; MeSO3-, Na+, Mg2+, Br- for aged marine emissions from the Pacific Ocean; arabitol, mannitol, K+ for biogenic emissions; Na+, Ca2+, Mg2+ for soil dust, and SO42-, F-, and some Cl- for volcanism. Regional biomass-burning practices influence the soluble fraction of the aerosol particularly between July and September. The organic fraction is present all year round and has both anthropogenic (biomass burning and other combustion sources) and natural (primary and secondary biogenic emissions) origins, with the OC/EC mass ratio being practically constant all year round (10.5±38.9). Peruvian volcanism dominates the SO42- concentration since 2014, though it presents a strong temporal variability due to the intermittence of the sources and seasonal changes on the transport patterns. These measurements represent some of the first long-term observations of aerosol chemical composition at a continental high-altitude site in the tropical Southern hemisphere.