| 1. |
- Eriksson, Axel, et al.
(författare)
-
Diesel soot aging in urban plumes within hours under cold dark and humid conditions
- 2017
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322.
-
Tidskriftsartikel (refereegranskat)abstract
- Fresh and aged diesel soot particles have different impacts on climate and human health. While fresh diesel soot particles are highly aspherical and non-hygroscopic, aged particles are spherical and hygroscopic. Aging and its effect on water uptake also controls the dispersion of diesel soot in the atmosphere. Understanding the timescales on which diesel soot ages in the atmosphere is thus important, yet knowledge thereof is lacking. We show that under cold, dark and humid conditions the atmospheric transformation from fresh to aged soot occurs on a timescale of less than five hours. Under dry conditions in the laboratory, diesel soot transformation is much less efficient. While photochemistry drives soot aging, our data show it is not always a limiting factor. Field observations together with aerosol process model simulations show that the rapid ambient diesel soot aging in urban plumes is caused by coupled ammonium nitrate formation and water uptake.
|
|
| 2. |
- Martinsson, Johan, et al.
(författare)
-
Carbonaceous aerosol source apportionment using the Aethalometer model - evaluation by radiocarbon and levoglucosan analysis at a rural background site in southern Sweden
- 2017
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:6, s. 4265-4281
-
Tidskriftsartikel (refereegranskat)abstract
- With the present demand on fast and inexpensive aerosol source apportionment methods, the Aethalometer model was evaluated for a full seasonal cycle (June 2014June 2015) at a rural atmospheric measurement station in southern Sweden by using radiocarbon and levoglucosan measurements. By utilizing differences in absorption of UV and IR, the Aethalometer model apportions carbon mass into wood burning (WB) and fossil fuel combustion (FF) aerosol. In this study, a small modification in the model in conjunction with carbon measurements from thermal-optical analysis allowed apportioned non-light-absorbing biogenic aerosol to vary in time. The absorption differences between WB and FF can be quantified by the absorption angstrom ngstrom exponent (AAE). In this study AAE(WB) was set to 1.81 and AAE(FF) to 1.0. Our observations show that the AAE was elevated during winter (1.36 +/- 0.07) compared to summer (1.12 +/- 0.07). Quantified WB aerosol showed good agreement with levoglucosan concentrations, both in terms of correlation (R-2 = 0 : 70) and in comparison to reference emission inventories. WB aerosol showed strong seasonal variation with high concentrations during winter (0.65 mu gm(-3), 56% of total carbon) and low concentrations during summer (0.07 mu gm(-3), 6% of total carbon). FF aerosol showed less seasonal dependence; however, black carbon (BC) FF showed clear diurnal patterns corresponding to traffic rush hour peaks. The presumed non-light-absorbing biogenic carbonaceous aerosol concentration was high during summer (1.04 mu gm(-3), 72% of total carbon) and low during winter (0.13 mu gm(-3), 8% of total carbon). Aethalometer model results were further compared to radiocarbon and levoglucosan source apportionment results. The comparison showed good agreement for apportioned mass of WB and biogenic carbonaceous aerosol, but discrepancies were found for FF aerosol mass. The Aethalometer model overestimated FF aerosol mass by a factor of 1.3 compared to radiocarbon and levoglucosan source apportionment. A performed sensitivity analysis suggests that this discrepancy can be explained by interference of non-light-absorbing biogenic carbon during winter. In summary, the Aethalometer model offers a costeffective yet robust high-time-resolution source apportionment at rural background stations compared to a radiocarbon and levoglucosan alternative.
|
|
| 3. |
- Öström, Emilie
(författare)
-
Modeling of new particle formation and growth in the atmospheric boundary layer
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric aerosols affect climate, but to what degree still remains one of the largest uncertainties in global climate models. To improve the representation of aerosols in future climate models we need a greater understanding of aerosol processes. In this thesis the process-based model ADCHEM has been used and further developed to study aerosol processes. Specifically; new particle formation and growth have been studied in boreal environments, but also over polluted marine environments.In the boreal forest, particles largely grow by condensation of oxidized organic compounds to form secondary organic aerosols (SOA). There are thousands of organic oxidation products and far from all are known, causing large uncertainties in the modeled aerosol population. Models that simulate the growth of particles must therefore make assumptions of which organic compounds, or group of compounds, that are potential condensation products and what properties they have. The modeled mass concentration of the resulting aerosol particles are dependent on the estimated saturation vapor pressures of the condensation products, but also on the further gas-phase aging of the organic oxidation products.Many models underestimate the SOA mass; one explanation could be missing gas-phase oxidation products. A newly proposed reaction pathway of monoterpenes containing endocyclic double bonds that form highly oxidized multifunctional organic molecules (HOMs) in the gas phase was implemented in the gas-phase chemistry module. The model was tested against observed HOM gas-phase composition and observed SOA formation during α-pinene ozonolysis experiments and field measurements. The model was able to reproduce the observed new particle formation events and particle growth if the HOM mechanism was included.ADCHEM was also used to study new particle formation in the marine boundary layer, to address whether particles formed over sea, or emitted anthropogenic gases over sea, have any importance on the cloud formation potential over land. If the air mass over the marine boundary layer is already polluted due to continental emissions, the importance of new particle formation over sea seems to be minor. The new particle formation and the further growth of particles are sensitive to the concentration of sulfuric acid. If strong new particle formation and rapid growth occurs close to the coast, the formed particles will act as a condensation sink for newly formed particles over land, with the potential to decrease the amount of particles that can act as cloud condensation nuclei over land.To achieve a greater understanding of aerosol processes and reduce the uncertainties in models, it is important that models are evaluated against observations at various locations and conditions. Much work remains to ensure that models give the right results for the right reasons.
|
|
| 4. |
- Öström, Emilie, et al.
(författare)
-
Modeling the role of highly oxidized multifunctional organic molecules for the growth of new particles over the boreal forest region
- 2017
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:14, s. 8887-8901
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the processes behind observed new particle formation (NPF) events and subsequent organic-dominated particle growth at the Pallas Atmosphere-Ecosystem Supersite in Northern Finland are explored with the one-dimensional column trajectory model ADCHEM. The modeled sub-micron particle mass is up to ∼75 % composed of SOA formed from highly oxidized multifunctional organic molecules (HOMs) with low or extremely low volatility. In the model the newly formed particles with an initial diameter of 1.5 nm reach a diameter of 7 nm about 2 h earlier than what is typically observed at the station. This is an indication that the model tends to overestimate the initial particle growth. In contrast, the modeled particle growth to CCN size ranges (> 50 nm in diameter) seems to be underestimated because the increase in the concentration of particles above 50 nm in diameter typically occurs several hours later compared to the observations. Due to the high fraction of HOMs in the modeled particles, the oxygen-to-carbon (O : C) atomic ratio of the SOA is nearly 1. This unusually high O : C and the discrepancy between the modeled and observed particle growth might be explained by the fact that the model does not consider any particle-phase reactions involving semi-volatile organic compounds with relatively low O : C. In the model simulations where condensation of low-volatility and extremely low-volatility HOMs explain most of the SOA formation, the phase state of the SOA (assumed either liquid or amorphous solid) has an insignificant impact on the evolution of the particle number size distributions. However, the modeled particle growth rates are sensitive to the method used to estimate the vapor pressures of the HOMs. Future studies should evaluate how heterogeneous reactions involving semi-volatility HOMs and other less-oxidized organic compounds can influence the SOA composition- and size-dependent particle growth.
|
|
