| 1. |
- Andersson, Erik, et al.
(författare)
-
Ambio fit for the 2020s
- 2022
-
Ingår i: Ambio. - : Springer Nature. - 0044-7447 .- 1654-7209. ; 51:5, s. 1091-1093
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
- Artaxo, Paulo, et al.
(författare)
-
Tropical and Boreal Forest – Atmosphere Interactions : A Review
- 2022
-
Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 74:1, s. 24-163
-
Forskningsöversikt (refereegranskat)abstract
- This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments.The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction.Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink.It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.
|
|
| 3. |
- Bell, David M., et al.
(författare)
-
Particle-phase processing of α-pinene NO3 secondary organic aerosol in the dark
- 2022
-
Ingår i: Atmospheric Chemistry and Physics. - 1680-7316 .- 1680-7324. ; 22, s. 13167-13182
-
Tidskriftsartikel (refereegranskat)abstract
- The NO3 radical represents a significant nighttime oxidant which is present downstream of polluted environments. Existing studies have investigated the formation of secondary organic aerosol (SOA) from NO3 radicals, focusing on the yields, general composition, and hydrolysis of organonitrates; however, there is limited knowledge about how the composition of NO3-derived SOA evolves as a result of particle-phase reactions. Here, SOA was formed from the reaction of α-pinene with NO3 radicals generated from N2O5, and the resulting SOA was aged in the dark. The initial composition of NO3-derived α-pinene SOA was slightly dependent upon the concentration of N2O5 injected (excess of NO3 or excess of α-pinene) but was largely dominated by dimer dinitrates (C20H32N2O8-13). Oxidation reactions (e.g., C20H32N2O8 → C20H32N2O9 → C20H32N2O10) accounted for 60 %-70 % of the particle-phase reactions observed. Fragmentation reactions and dimer degradation pathways made up the remainder of the particle-phase processes occurring. The exact oxidant is not known, although suggestions are offered (e.g., N2O5, organic peroxides, or peroxynitrates). Hydrolysis of -ONO2 functional groups was not an important loss term during dark aging under the relative humidity conditions of our experiments (58 %-62 %), and changes in the bulk organonitrate composition were likely driven by evaporation of highly nitrogenated molecules. Overall, 25 %-30 % of the particle-phase composition changes as a function of particle-phase reactions during dark aging, representing an important atmospheric aging pathway.
|
|
| 4. |
- Bell, David M., et al.
(författare)
-
Particle-phase processing of α-pinene NO3 secondary organic aerosol in the dark
- 2022
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 22:19, s. 13167-13182
-
Tidskriftsartikel (refereegranskat)abstract
- The NO3 radical represents a significant night-time oxidant present in or downstream of polluted environments. There are studies that investigated the formation of secondary organic aerosol (SOA) from NO3 radicals focusing on yields, general composition, and hydrolysis of organonitrates. However, there is limited knowledge about how the composition of NO3-derived SOA evolves as a result of particle phase reactions. Here, SOA was formed from the reaction of α-pinene with NO3 radicals generated from N2O5, and the resulting SOA aged in the absence of external stimuli. The initial composition of NO3-derived α-pinene SOA was slightly dependent upon the concentration of N2O5 injected (excess of NO3 or excess of α-pinene), but was largely dominated by dimer dinitrates (C20H32N2O8-13). Oxidation reactions (e.g. C20H32N2O8 → C20H32N2O9 → C20H32N2O10 etc...) accounted for 60–70 % of the particle phase reactions observed. Fragmentation reactions and dimer degradation pathways made up the remainder of the particle-phase processes occurring. The exact oxidant is not known, though suggestions are offered (e.g. N2O5, organic peroxides, or peroxy-nitrates). Hydrolysis of −ONO2 functional groups was not an important loss term during dark aging under the relative humidity conditions of our experiments (58–62 %), and changes in the bulk organonitrate composition were likely driven by evaporation of highly nitrogenated molecules. Overall, 25–30 % of the particle-phase composition changes as a function of particle-phase reactions during dark aging representing an important atmospheric aging pathway.
|
|
| 5. |
- Bianchi, Federico, et al.
(författare)
-
Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals : A Key Contributor to Atmospheric Aerosol
- 2019
-
Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 119:6, s. 3472-3509
-
Forskningsöversikt (refereegranskat)abstract
- Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earths radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research.
|
|
| 6. |
- Bianchi, F., et al.
(författare)
-
The SALTENA Experiment : Comprehensive Observations of Aerosol Sources, Formation, and Processes in the South American Andes
- 2022
-
Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 103:2, s. E212-E229
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an introduction to the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5,240 m MSL in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4,000 m MSL) and La Paz (3,600 m MSL). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, airmass origin, and boundary layer-free troposphere interactions during the campaign using a 6-month high-resolution Weather Research and Forecasting (WRF) simulation coupled with Flexible Particle dispersion model (FLEXPART). We then show some of the research highlights from the campaign, including (i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz-El Alto, (ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, (iii) the characterization of the compounds involved in new particle formation, and (iv) the identification of long-range-transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere.
|
|
| 7. |
- Blichner, Sara M., 1989-, et al.
(författare)
-
Process-evaluation of forest aerosol-cloud-climate feedback shows clear evidence from observations and large uncertainty in models
- 2024
-
Ingår i: Nature Communications. - 2041-1723. ; 15
-
Tidskriftsartikel (refereegranskat)abstract
- Natural aerosol feedbacks are expected to become more important in the future, as anthropogenic aerosol emissions decrease due to air quality policy. One such feedback is initiated by the increase in biogenic volatile organic compound (BVOC) emissions with higher temperatures, leading to higher secondary organic aerosol (SOA) production and a cooling of the surface via impacts on cloud radiative properties. Motivated by the considerable spread in feedback strength in Earth System Models (ESMs), we here use two long-term observational datasets from boreal and tropical forests, together with satellite data, for a process-based evaluation of the BVOC-aerosol-cloud feedback in four ESMs. The model evaluation shows that the weakest modelled feedback estimates can likely be excluded, but highlights compensating errors making it difficult to draw conclusions of the strongest estimates. Overall, the method of evaluating along process chains shows promise in pin-pointing sources of uncertainty and constraining modelled aerosol feedbacks.
|
|
| 8. |
- Buchholz, Angela, et al.
(författare)
-
Deconvolution of FIGAERO-CIMS thermal desorption profiles using positive matrix factorisation to identify chemical and physical processes during particle evaporation
- 2020
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:13, s. 7693-7716
-
Tidskriftsartikel (refereegranskat)abstract
- The measurements of aerosol particles with a filter inlet for gases and aerosols (FIGAERO) together with a chemical ionisation mass spectrometer (CIMS) yield the overall chemical composition of the particle phase. In addition, the thermal desorption profiles obtained for each detected ion composition contain information about the volatility of the detected compounds, which is an important property for understanding many physical properties like gas-particle partitioning. We coupled this thermal desorption method with isothermal evaporation prior to the sample collection to investigate the chemical composition changes during isothermal particle evaporation and particulate-water-driven chemical reactions in alpha-pinene secondary organic aerosol (SOA) of three different oxidative states. The thermal desorption profiles of all detected elemental compositions were then analysed with positive matrix factorisation (PMF) to identify the drivers of the chemical composition changes observed during isothermal evaporation. The keys to this analysis were to use the error matrix as a tool to weight the parts of the data carrying most information (i.e. the peak area of each thermogram) and to run PMF on a combined data set of multiple thermograms from different experiments to enable a direct comparison of the individual factors between separate measurements. The PMF was able to identify instrument background factors and separate them from the part of the data containing particle desorption information. Additionally, PMF allowed us to separate the direct desorption of compounds detected at a specific elemental composition from other signals with the same composition that stem from the thermal decomposition of thermally instable compounds with lower volatility. For each SOA type, 7-9 factors were needed to explain the observed thermogram behaviour. The contribution of the factors depended on the prior isothermal evaporation. Decreased contributions from the factors with the lowest desorption temperatures were observed with increasing isothermal evaporation time. Thus, the factors identified by PMF could be interpreted as volatility classes. The composition changes in the particles due to isothermal evaporation could be attributed to the removal of volatile factors with very little change in the desorption profiles of the individual factors (i.e. in the respective temperatures of peak desorption, T-max). When aqueous-phase reactions took place, PMF was able to identify a new factor that directly identified the ions affected by the chemical processes. We conducted a PMF analysis of the FIGAERO-CIMS thermal desorption data for the first time using laboratory-generated SOA particles. But this method can be applied to, for example, ambient FIGAERO-CIMS measurements as well. There, the PMF analysis of the thermal desorption data identifies organic aerosol (OA) sources (such as biomass burning or oxidation of different precursors) and types, e.g. hydrocarbon-like (HOA) or oxygenated organic aerosol (OOA). This information could also be obtained with the traditional approach, namely the PMF analysis of the mass spectra data integrated for each thermogram. But only our method can also obtain the volatility information for each OA source and type. Additionally, we can identify the contribution of thermal decomposition to the overall signal.
|
|
| 9. |
- Buchholz, Angela, et al.
(författare)
-
Insights into the O : C-dependent mechanisms controlling the evaporation of alpha-pinene secondary organic aerosol particles
- 2019
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:6, s. 4061-4073
-
Tidskriftsartikel (refereegranskat)abstract
- The volatility of oxidation products of volatile organic compounds (VOCs) in the atmosphere is a key factor to determine if they partition into the particle phase contributing to secondary organic aerosol (SOA) mass. Thus, linking volatility and measured particle composition will provide insights into SOA formation and its fate in the atmosphere. We produced alpha-pinene SOA with three different oxidation levels (characterized by average oxygen-to-carbon ratio; (O:C) over bar = 0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the particle volatility by isothermal evaporation in clean air as a function of relative humidity (RH < 2 %, 40 %, and 80 %) and used a filter-based thermal desorption method to gain volatility and chemical composition information. We observed reduced particle evaporation for particles with increasing <(O:C )over bar> ratio, indicating that particles become more resilient to evaporation with oxidative aging. Particle evaporation was increased in the presence of water vapour and presumably particulate water; at the same time the resistance of the residual particles to thermal desorption was increased as well. For SOA with (O:C ) over bar = 0.96, the unexpectedly large increase in mean thermal desorption temperature and changes in the thermogram shapes under wet conditions (80 % RH) were an indication of aqueous phase chemistry. For the lower (O:C ) over bar cases, some water-induced composition changes were observed. However, the enhanced evaporation under wet conditions could be explained by the reduction in particle viscosity from the semi-solid to liquid-like range, and the observed higher desorption temperature of the residual particles is a direct consequence of the increased removal of high-volatility and the continued presence of low-volatility compounds.
|
|
| 10. |
- Cai, Jing, et al.
(författare)
-
Characterization of offline analysis of particulate matter with FIGAERO-CIMS
- 2023
-
Ingår i: Atmospheric Measurement Techniques (AMT). - : Copernicus GmbH. - 1867-8610 .- 1867-8548 .- 1867-1381. ; 16:5, s. 1147-1165
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the molecular composition of organic aerosol (OA) constituents improve our understanding of sources, formation processes, and physicochemical properties of OA. One instrument providing such data at a time resolution of minutes to hours is the chemical ionization time-of-flight mass spectrometer with filter inlet for gases and aerosols (FIGAERO-CIMS). The technique collects particles on a filter, which are subsequently desorbed, and the evaporated molecules are ionized and analyzed in the mass spectrometer. However, long-term measurements using this technique and/or field deployments at several sites simultaneously require substantial human and financial resources. The analysis of filter samples collected outside the instrument (offline) may provide a more cost-efficient alternative and makes this technology available for the large number of particle filter samples collected routinely at many different sites globally. Filter-based offline use of the FIGAERO-CIMS limits this method, albeit to particle-phase analyses, which is likely at a reduced time resolution compared to online deployments. Here we present the application and assessment of offline FIGAERO-CIMS, using Teflon and quartz fiber filter samples that were collected in autumn 2018 in urban Beijing. We demonstrate the feasibility of the offline application with a “sandwich” sample preparation for the over 900 identified organic compounds with (1) high signal-to-noise ratios, (2) high repeatability, and (3) linear signal response to the filter loadings. Comparable overall signals were observed between the quartz fiber and Teflon filters for 12 and 24h samples but with larger signals for semi-volatile compounds for the quartz fiber filters, likely due to adsorption artifacts. We also compare desorption profile (thermogram) shapes for the two filter materials. Thermograms are used to derive volatility qualitatively based on the desorption temperature at which the maximum signal intensity of a compound is observed (Tmax). While we find that Tmax can be determined with high repeatability (±5.7∘C) from the duplicate tests for one filter type, we observe considerable differences in Tmax between the quartz and Teflon filters, warranting further investigation into the thermal desorption characteristics of different filter types. Overall, this study provides a basis for expanding OA molecular characterization by FIGAERO-CIMS to situations where and when deployment of the instrument itself is not possible.
|
|
