scholarly journals Supplementary material to "Aerosol optical properties calculated from size distributions, filter samples and absorption photometer data at Dome C, Antarctica and their relationships between seasonal cycles of sources"

2021 ◽  
Author(s):  
Aki Virkkula ◽  
Henrik Grythe ◽  
John Backman ◽  
Tuukka Petäjä ◽  
Maurizio Busetto ◽  
...  
Keyword(s):  
Optical Properties ◽  
Seasonal Cycles ◽  
Size Distributions ◽  
Aerosol Optical Properties ◽  
Supplementary Material ◽  
Absorption Photometer

scholarly journals Estimating cloud condensation nuclei number concentrations using aerosol optical properties: role of particle number size distribution and parameterization

2019 ◽  
Vol 19 (24) ◽  
pp. 15483-15502 ◽  
Author(s):  
Yicheng Shen ◽  
Aki Virkkula ◽  
Aijun Ding ◽  
Krista Luoma ◽  
Helmi Keskinen ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Cloud Condensation Nuclei ◽  
Size Distributions ◽  
Condensation Nuclei ◽  
Aerosol Optical Properties ◽  
Average Bias ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. The concentration of cloud condensation nuclei (CCN) is an essential parameter affecting aerosol–cloud interactions within warm clouds. Long-term CCN number concentration (NCCN) data are scarce; there are a lot more data on aerosol optical properties (AOPs). It is therefore valuable to derive parameterizations for estimating NCCN from AOP measurements. Such parameterizations have already been made, and in the present work a new parameterization is presented. The relationships between NCCN, AOPs, and size distributions were investigated based on in situ measurement data from six stations in very different environments around the world. The relationships were used for deriving a parameterization that depends on the scattering Ångström exponent (SAE), backscatter fraction (BSF), and total scattering coefficient (σsp) of PM10 particles. The analysis first showed that the dependence of NCCN on supersaturation (SS) can be described by a logarithmic fit in the range SS <1.1 %, without any theoretical reasoning. The relationship between NCCN and AOPs was parameterized as NCCN≈((286±46)SAE ln(SS/(0.093±0.006))(BSF − BSFmin) + (5.2±3.3))σsp, where BSFmin is the minimum BSF, in practice the 1st percentile of BSF data at a site to be analyzed. At the lowest supersaturations of each site (SS ≈0.1 %), the average bias, defined as the ratio of the AOP-derived and measured NCCN, varied from ∼0.7 to ∼1.9 at most sites except at a Himalayan site where the bias was >4. At SS >0.4 % the average bias ranged from ∼0.7 to ∼1.3 at most sites. For the marine-aerosol-dominated site Ascension Island the bias was higher, ∼1.4–1.9. In other words, at SS >0.4 % NCCN was estimated with an average uncertainty of approximately 30 % by using nephelometer data. The biases were mainly due to the biases in the parameterization related to the scattering Ångström exponent (SAE). The squared correlation coefficients between the AOP-derived and measured NCCN varied from ∼0.5 to ∼0.8. To study the physical explanation of the relationships between NCCN and AOPs, lognormal unimodal particle size distributions were generated and NCCN and AOPs were calculated. The simulation showed that the relationships of NCCN and AOPs are affected by the geometric mean diameter and width of the size distribution and the activation diameter. The relationships of NCCN and AOPs were similar to those of the observed ones.

scholarly journals Aerosol Optical Properties at SORPES in Nanjing, East China

2017 ◽  
Author(s):  
Yicheng Shen ◽  
Aki Virkkula ◽  
Aijun Ding ◽  
Jiaping Wang ◽  
Xuguang Chi ◽  
...  
Keyword(s):  
Optical Properties ◽  
Growth Phase ◽  
Radiative Forcing ◽  
Mass Fraction ◽  
Particle Number ◽  
Eastern China ◽  
Green Light ◽  
Seasonal Cycles ◽  
Aerosol Optical Properties ◽  
Pollution Episodes

Abstract. Aerosol optical properties (AOPs) and supporting parameters – particle number size distributions, mass concentrations and trace gases (NOx and NOy) – were measured at SORPES, a regional background station in Nanjing, China from June 2013 to May 2015. The aerosol was highly scattering: the average scattering coefficient was σsp = 410 ± 320 Mm−1, the absorption coefficient σap = 26 ± 19 Mm−1 and the single-scattering albedo SSA = 0.93 ± 0.03 for the green light. The SSA in Nanjing appears to be slightly higher than published values from several other sites in China and elsewhere. The average Ångström exponent of absorption (AAE) for the wavelength range 370–950 nm was 1.04 and the AAE range 0.7–1.4. These AAE values can be explained with different amounts of non-absorbing coating on pure BC cores and different core sizes so the data does not suggest any significant contribution to absorption by brown carbon. The AOPs had typical seasonal cycles with high σsp and σap in winter and lower in summer: the averages were σsp = 545 ± 425 Mm−1 and σap = 36 ± 24 Mm−1 in winter and σsp = 364 ± 294 Mm−1 and σap = 20 ± 13 Mm−1 in summer. The intensive AOPs had no clear seasonal cycles, the variations of them were rather related to the evolution of pollution episodes. The diurnal cycles of the intensive AOPs were clear and in in agreement with the cycle of the particle number size distribution. The diurnal cycle of SSA was similar to that of the air photochemical age, suggesting that the darkest aerosol originated from fresh traffic emissions. A Lagrangian retroplume analysis showed that the sources of high σsp and σap are mainly in eastern China. Synoptic weather dominated the cycle of AOPs in a temporal scale of 2–7 days. During pollution episodes, modeled PBLH decreased, whereas PM2.5 concentrations, σsp and σap typically increased gradually and remained high during several days but decreased faster, sometimes by even more than an order of magnitude within some hours. During the growth phase of the pollution episodes the intensive AOPs evolved clearly. The mass scattering efficiency MSE of of PM2.5 grew during the extended pollution episodes from ~4 m2 g−1 to ~6 m2 g−1 and the mass fraction of BCe decreased from ~10 % to ~2 % during the growth phase of the episodes. Particle growth resulted in b decreasing from more than 0.16 to less than 0.10, SSA growing from less than 0.9 to more than 0.95 and radiative forcing efficiency RFE growing from less than −26 W m−2 τ−1 to more than −24 W m−2 τ−1. In other words, the darker aerosol – the aerosol that had a higher BC mass fraction – had a more negative radiative forcing efficiency, i.e., they have the property of cooling the atmosphere more efficiently per unit optical depth than the aerosol with the higher SSA and a lower BC mass fraction. This counterintuitive result is due to the size of the particles: the upscatter fraction of small particles is higher than that of the big ones which more than compensates the darkness of them. The RFE probability distribution at SORPES was clearly more narrow than at a clean background site which is in agreement with a published RFE climatology.

scholarly journals Aerosol optical properties at SORPES in Nanjing, east China

2018 ◽  
Vol 18 (8) ◽  
pp. 5265-5292 ◽  
Author(s):  
Yicheng Shen ◽  
Aki Virkkula ◽  
Aijun Ding ◽  
Jiaping Wang ◽  
Xuguang Chi ◽  
...  
Keyword(s):  
Optical Properties ◽  
Growth Phase ◽  
Radiative Forcing ◽  
Particle Number ◽  
Eastern China ◽  
Green Light ◽  
Particle Growth ◽  
Seasonal Cycles ◽  
Aerosol Optical Properties ◽  
Pollution Episodes

Abstract. Aerosol optical properties (AOPs) and supporting parameters – particle number size distributions, PM2.5 mass concentrations, and the concentrations of trace gases (NOx and NOy) – were measured at SORPES, a regional background station in Nanjing, China from June 2013 to May 2015. The aerosol was highly scattering: the average scattering coefficient was σsp=403 ± 314 Mm−1, the absorption coefficient σap=26 ± 19 Mm−1, and the single-scattering albedo SSA = 0.93 ± 0.03 for green light. The SSA in Nanjing appears to be slightly higher than published values from several other sites in China and elsewhere. The average Ångström exponent of absorption (AAE) for the wavelength range 370–950 nm was 1.04 and the AAE range was 0.7–1.4. These AAE values can be explained with different amounts of non-absorbing coating on pure black carbon (BC) cores and different core sizes rather than contribution by brown carbon. The AOPs had typical seasonal cycles with high σsp and σap in winter and low ones in summer: the averages were σsp=544 ± 422 and σap=36 ± 24 Mm−1 in winter and σsp=342 ± 281 and σap=20 ± 13 Mm−1 in summer. The intensive AOPs had no clear seasonal cycles, the variations in them were rather related to the evolution of pollution episodes. The diurnal cycles of the intensive AOPs were clear and in agreement with the cycle of the particle number size distribution. The diurnal cycle of SSA was similar to that of the air photochemical age, suggesting that the darkest aerosol originated from fresh traffic emissions. A Lagrangian retroplume analysis showed that the potential source areas of high σsp and σap are mainly in eastern China. Synoptic weather phenomena dominated the cycle of AOPs on a temporal scale of 3–7 days. During pollution episodes, modeled boundary layer height decreased, whereas PM2.5 concentrations and σsp and σap typically increased gradually and remained high during several days but decreased faster, sometimes by even more than an order of magnitude within some hours. During the growth phase of the pollution episodes the intensive AOPs evolved clearly. The mass scattering efficiency MSE of PM2.5 grew during the extended pollution episodes from ∼ 4 to ∼ 6 m2 g−1 and the mass fraction of BCe decreased from ∼ 10 to ∼ 3 % during the growth phase of the episodes. Particle growth resulted in the backscatter fraction decreasing from more than 0.16 to less than 0.10, SSA growing from less than 0.9 to more than 0.95, and radiative forcing efficiency (RFE) changing from less than −26 W m−2 to more than −24 W m−2, which means that the magnitude of RFE decreased. The RFE probability distribution at SORPES was clearly narrower than at a clean background site which is in agreement with a published RFE climatology.

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