scholarly journals Volatility of mixed atmospheric humic-like substances and ammonium sulfate particles

2017 ◽  
Vol 17 (5) ◽  
pp. 3659-3672 ◽  
Author(s):  
Wei Nie ◽  
Juan Hong ◽  
Silja A. K. Häme ◽  
Aijun Ding ◽  
Yugen Li ◽  
...  
Keyword(s):  
Ammonium Sulfate ◽  
Volume Fraction ◽  
Eastern China ◽  
Organic Aerosols ◽  
Organic Aerosol ◽  
Yangtze River Delta ◽  
Inorganic Salts ◽  
Transfer Model ◽  
Organic Part ◽  
Mixed Samples

Abstract. The volatility of organic aerosols remains poorly understood due to the complexity of speciation and multiphase processes. In this study, we extracted humic-like substances (HULIS) from four atmospheric aerosol samples collected at the SORPES station in Nanjing, eastern China, and investigated the volatility behavior of particles at different sizes using a Volatility Tandem Differential Mobility Analyzer (VTDMA). In spite of the large differences in particle mass concentrations, the extracted HULIS from the four samples all revealed very high-oxidation states (O : C > 0.95), indicating secondary formation as the major source of HULIS in Yangtze River Delta (YRD). An overall low volatility was identified for the extracted HULIS, with the volume fraction remaining (VFR) higher than 55 % for all the regenerated HULIS particles at the temperature of 280 °C. A kinetic mass transfer model was applied to the thermodenuder (TD) data to interpret the observed evaporation pattern of HULIS, and to derive the mass fractions of semi-volatile (SVOC), low-volatility (LVOC) and extremely low-volatility components (ELVOC). The results showed that LVOC and ELVOC dominated (more than 80 %) the total volume of HULIS. Atomizing processes led to a size-dependent evaporation of regenerated HULIS particles, and resulted in more ELVOC in smaller particles. In order to understand the role of interaction between inorganic salts and atmospheric organic mixtures in the volatility of an organic aerosol, the evaporation of mixed samples of ammonium sulfate (AS) and HULIS was measured. The results showed a significant but nonlinear influence of ammonium sulfate on the volatility of HULIS. The estimated fraction of ELVOC in the organic part of the largest particles (145 nm) increased from 26 %, in pure HULIS samples, to 93 % in 1 : 3 (mass ratio of HULIS : AS) mixed samples, to 45 % in 2 : 2 mixed samples, and to 70 % in 3 : 1 mixed samples, suggesting that the interaction with ammonium sulfate tends to decrease the volatility of atmospheric organic compounds. Our results demonstrate that HULIS are important low-volatility, or even extremely low-volatility, compounds in the organic-aerosol phase. As important formation pathways of atmospheric HULIS, multiphase processes, including oxidation, oligomerization, polymerization and interaction with inorganic salts, are indicated to be important sources of low-volatility and extremely low-volatility species of organic aerosols.

scholarly journals Volatility of mixed atmospheric Humic-like Substances and ammonium sulfate particles

2016 ◽  
Author(s):  
Wei Nie ◽  
Juan Hong ◽  
Silja A. K. Häme ◽  
Aijun Ding ◽  
Yugen Li ◽  
...  
Keyword(s):  
Ammonium Sulfate ◽  
Volume Fraction ◽  
Eastern China ◽  
Organic Aerosols ◽  
Organic Aerosol ◽  
Inorganic Salts ◽  
Transfer Model ◽  
Organic Part ◽  
Multi Phase ◽  
Mixed Samples

Abstract. The volatility of organic aerosols remains poorly understood due to the complexity of speciation and multi-phase processes. In this study, we extracted HUmic-LIke Substances (HULIS) from four atmospheric aerosol samples collected at the SORPES station in Nanjing, eastern China, and investigated the volatility behavior of particles at different sizes using a Volatility Tandem Differential Mobility Analyzer (VTDMA). In spite of the large differences in particle mass concentrations, the extracted HULIS from the four samples all revealed very high oxidation states (O : C > 0.95), indicating secondary formation as the major source of HULIS in Yangtze River Delta (YRD). An overall low volatility was identified for the HULIS samples, with the volume fraction remaining (VFR) higher than 55 % for all the re-generated HULIS particles at the temperature of 280 °C. A kinetic mass transfer model was applied to the thermodenuder (TD) data to interpret the observed evaporation pattern of HULIS, and to derive the mass fractions of semi-volatile (SVOC), low-volatility (LVOC) and extremely low-volatility components (ELVOC). The results showed that LVOC and ELVOC dominated (more than 80 %) the total volume of HULIS. Atomizing processes led to a size dependent evaporation of regenerated HULIS particles, and resulted in more ELVOCs in smaller particles. In order to understand the role of interaction between inorganic salts and atmospheric organic mixtures in the volatility of an organic aerosol, the evaporation of mixed samples of ammonium sulfate (AS) and HULIS was measured. The results showed a significant but nonlinear influence of ammonium sulfate on the volatility of HULIS. The estimated fraction of ELVOCs in the organic part of largest particles (145 nm) increased from 26 % in pure HULIS samples to 93 % in 1 : 3 (mass ratio of HULIS : AS) mixed samples, to 45 % in 2 : 2 mixed samples, and to 70 % in 3 : 1 mixed samples, suggesting that the interaction tends to decrease the volatility of atmospheric organic molecular once condensing on ammonium sulfate containing aerosols. Our results demonstrate that HULIS are important low volatile, or even extremely low volatile, compounds in the organic aerosol phase. As important formation pathways of atmospheric HULIS, multi-phase processes, including oxidation, oligomerization, polymerization and interaction with inorganic salts, are indicated to be important sources of low volatile and extremely low volatility species of organic aerosols.

scholarly journals Insights on organic aerosol aging and the influence of coal combustion at a regional receptor site of Central Eastern China

2013 ◽  
Vol 13 (4) ◽  
pp. 10809-10858 ◽  
Author(s):  
W. W. Hu ◽  
M. Hu ◽  
B. Yuan ◽  
J. L. Jimenez ◽  
Q. Tang ◽  
...  
Keyword(s):  
High Resolution ◽  
Black Carbon ◽  
Coal Combustion ◽  
Eastern China ◽  
Organic Aerosols ◽  
Receptor Site ◽  
Organic Aerosol ◽  
Submicron Particles ◽  
Central Eastern ◽  
Photochemical Age

Abstract. In order to understand the aging and processing of organic aerosols (OA), an intensive field campaign (Campaign of Air Pollution at Typical Coastal Areas In Eastern China, CAPTAIN) was conducted in March–April at a receptor site (Changdao Island) in Central Eastern China. Multiple fast aerosol and gas measurement instruments were used during the campaign, including a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was applied to measure mass concentrations and non-refractory chemical components of submicron particles (PM1nr). The average mass concentration of PM1 (PM1nr + black carbon) was 47 ± 36 μg m−3 during the campaign and showed distinct variation depending on back trajectories and their overlap with source regions. Organic aerosol (OA) is the largest component of PM1 (30%), followed by nitrate (28%), sulfate (19%), ammonium (15%), black carbon (6%), and chloride (3%). Four OA components were resolved by Positive Matrix Factorization (PMF) of the high-resolution spectra, including low-volatility oxygenated organic aerosol (LV-OOA), semi-volatile oxygenated OA (SV-OOA), hydrocarbon-like OA (HOA) and a coal combustion OA (CCOA), reported here for the first time. The mass spectrum of CCOA has high abundance of fragments from polycyclic aromatic hydrocarbons (PAHs) (m/z 128, 152, 178 etc.). The average atomic ratio of oxygen to carbon in OA (O/C) at Changdao is 0.59, which is comparable to other field studies reported at locations downwind of large pollution sources, indicating the oxidized nature of most OA during the campaign. The evolution of OA elemental composition in the Van Krevelen diagram (H/C vs. O/C) shows a slope of −0.63, however, the OA influenced by coal combution exhibits a completely different evolution that appears dominated by physical mixing. The aging of organic aerosols vs. with photochemical age was investigated. It is shown that OA/ΔCO, as well as LV-OOA/ΔCO and SV-OOA/ΔCO, positively correlated with photochemical age. LV-OOA accounted for 73% of the OA secondary formation in the oldest plumes (photochemical age of 25 h). The kOH at Changdao by assuming SOA formation and aging as a first-order process proportional to OH was calculated to be is 5.2 × 10−12 cm3 molec−1 s−1 which is similar to those determined in recent studies of polluted air in other continents.

scholarly journals Insights on organic aerosol aging and the influence of coal combustion at a regional receptor site of central eastern China

2013 ◽  
Vol 13 (19) ◽  
pp. 10095-10112 ◽  
Author(s):  
W. W. Hu ◽  
M. Hu ◽  
B. Yuan ◽  
J. L. Jimenez ◽  
Q. Tang ◽  
...  
Keyword(s):  
High Resolution ◽  
Black Carbon ◽  
Coal Combustion ◽  
Eastern China ◽  
Organic Aerosols ◽  
Receptor Site ◽  
Organic Aerosol ◽  
Submicron Particles ◽  
Central Eastern ◽  
Photochemical Age

Abstract. In order to understand the aging and processing of organic aerosols (OA), an intensive field campaign (Campaign of Air Pollution at Typical Coastal Areas IN Eastern China, CAPTAIN) was conducted March–April at a receptor site (a Changdao island) in central eastern China. Multiple fast aerosol and gas measurement instruments were used during the campaign, including a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) that was applied to measure mass concentrations and non-refractory chemical components of submicron particles (PM1nr). The average mass concentration of PM1(PM1nr+black carbon) was 47 ± 36 μg m−3 during the campaign and showed distinct variation, depending on back trajectories and their overlap with source regions. Organic aerosol (OA) is the largest component of PM1 (30%), followed by nitrate (28%), sulfate (19%), ammonium (15%), black carbon (6%), and chloride (3%). Four OA components were resolved by positive matrix factorization (PMF) of the high-resolution spectra, including low-volatility oxygenated organic aerosol (LV-OOA), semi-volatile oxygenated OA (SV-OOA), hydrocarbon-like OA (HOA) and a coal combustion OA (CCOA). The mass spectrum of CCOA had high abundance of fragments from polycyclic aromatic hydrocarbons (PAHs) (m/z 128, 152, 178, etc.). The average atomic ratio of oxygen to carbon in OA (O / C) at Changdao was 0.59, which is comparable to other field studies reported at locations downwind of large pollution sources, indicating the oxidized nature of most OA during the campaign. The evolution of OA elemental composition in the van Krevelen diagram (H / C vs. O / C) showed a slope of −0.63; however, the OA influenced by coal combustion exhibits a completely different evolution that appears dominated by physical mixing. The aging of organic aerosols vs. photochemical age was investigated. It was shown that OA / ΔCO, as well as LV-OOA / ΔCO and SV-OOA / ΔCO, positively correlated with photochemical age. LV-OOA accounted for 73% of the OA secondary formation (SOA) in the oldest plumes (photochemical age of 25 h). The kOH at Changdao, by assuming SOA formation and aging as a first-order process proportional to OH, was calculated to be 5.2 × 10−12 cm3 molec.−1 s−1, which is similar to those determined in recent studies of polluted air in other continents.

scholarly journals The optical properties, physical properties and direct radiative forcing of urban columnar aerosols in the Yangtze River Delta, China

2018 ◽  
Vol 18 (2) ◽  
pp. 1419-1436 ◽  
Author(s):  
Bingliang Zhuang ◽  
Tijian Wang ◽  
Jane Liu ◽  
Huizheng Che ◽  
Yong Han ◽  
...  
Keyword(s):  
Optical Properties ◽  
Physical Properties ◽  
Yangtze River ◽  
Eastern China ◽  
Yangtze River Delta ◽  
River Delta ◽  
Transfer Model ◽  
Size Distributions ◽  
Haze Pollution ◽  
The Yrd

Abstract. The optical and physical properties as well as the direct radiative forcings (DRFs) of fractionated aerosols in the urban area of the western Yangtze River Delta (YRD) are investigated with measurements from a Cimel sun photometer combined with a radiation transfer model. Ground-based observations of aerosols have much higher temporal resolutions than satellite retrievals. An initial analysis reveals the characteristics of the optical properties of different types of fractionated aerosols in the western YRD. The total aerosols, mostly composed of scattering components (93.8 %), have mean optical depths of 0.65 at 550 nm and refractive index of 1.44 + 0.0084i at 440 nm. The fine aerosols are approximately four times more abundant and have very different compositions from coarse aerosols. The absorbing components account for only  ∼  4.6 % of fine aerosols and 15.5 % of coarse aerosols and have smaller sizes than the scattering aerosols within the same mode. Therefore, fine particles have stronger scattering than coarse ones, simultaneously reflecting the different size distributions between the absorbing and scattering aerosols. The relationships among the optical properties quantify the aerosol mixing and imply that approximately 15 and 27.5 % of the total occurrences result in dust- and black-carbon-dominating mixing aerosols, respectively, in the western YRD. Unlike the optical properties, the size distributions of aerosols in the western YRD are similar to those found at other sites over eastern China on a climatological scale, peaking at radii of 0.148 and 2.94 µm. However, further analysis reveals that the coarse-dominated particles can also lead to severe haze pollution over the YRD. Observation-based estimations indicate that both fine and coarse aerosols in the western YRD exert negative DRFs, and this is especially true for fine aerosols (−11.17 W m−2 at the top of atmosphere, TOA). A higher absorption fraction leads directly to the negative DRF being further offset for coarse aerosols (−0.33 W m−2) at the TOA. Similarly, the coarse-mode DRF contributes to only 13.3 % of the total scattering aerosols but > 33.7 % to the total absorbing aerosols. A sensitivity analysis states that aerosol DRFs are not highly sensitive to their profiles in clear-sky conditions. Most of the aerosol properties and DRFs have substantial seasonality in the western YRD. The results further reveal the contributions of each component of the different size particles to the total aerosol optical depths (AODs) and DRFs. Additionally, these results can be used to improve aerosol modelling performance and the modelling of aerosol effects in the eastern regions of China.

scholarly journals Urban organic aerosol composition in Eastern China differs from North to South: Molecular insight from a liquid chromatography-Orbitrap mass spectrometry study

2019 ◽  
Author(s):  
Kai Wang ◽  
Ru-Jin Huang ◽  
Martin Brüggemann ◽  
Yun Zhang ◽  
Lu Yang ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Liquid Chromatography ◽  
Eastern China ◽  
Organic Aerosol ◽  
Photochemical Oxidation ◽  
Lower Latitude ◽  
Molecular Formula ◽  
Aerosol Composition ◽  
Orbitrap Mass Spectrometry ◽  
Low Degrees

Abstract. Particulate air pollution in China is influencing human health, ecosystem and climate. However, the chemical composition of particulate aerosol, especially of the organic fraction, is still not well understood. In this study, particulate aerosol samples with a diameter ≤ 2.5 μm (PM2.5) were collected in January 2014 in three cities located in Northeast, East and Southeast China, i.e., Changchun, Shanghai and Guangzhou, respectively. Organic aerosol (OA) in the PM2.5 samples was analyzed by ultrahigh performance liquid chromatography (UHPLC) coupled to high-resolution Orbitrap mass spectrometry in both negative mode (ESI−) and positive mode electrospray ionization (ESI+). After a non-target screening including molecular formula assignments, compounds were classified into five groups based on their elemental composition, i.e., CHO, CHON, CHN, CHOS and CHONS. The CHO, CHON and CHN compounds present the dominant signal abundances of 81–99.7 % in the mass spectra and the majority of these compounds were assigned to mono- and polyaromatics, suggesting that anthropogenic emissions are a large source of urban OA in all three cities. However, the chemical characteristics of these compounds varied among different cities. The degree of aromaticity and the number of polyaromatic compounds were significantly higher in samples from Changchun, which could be attributed to the large emissions from residential heating (i.e., coal combustion) during winter time in Northeast China. Moreover, the ESI− analysis showed higher H / C and O / C ratios for organic compounds in Shanghai and Guangzhou compared to samples from Changchun, indicating that OA in lower latitude regions of China experiences more intense photochemical oxidation processes. The majority of sulfur-containing compounds (CHOS and CHONS) in all cities were assigned to aliphatic compounds with low degrees of unsaturation and aromaticity. Again, samples from Shanghai and Guangzhou exhibit a larger chemical similarity but largely differ from those from Changchun.

scholarly journals Ozone formation under low solar radiation in eastern China

2019 ◽  
Author(s):  
Xuexi Tie ◽  
Xin Long ◽  
Guohui Li ◽  
Shuyu Zhao ◽  
Jianming Xu
Keyword(s):  
Solar Radiation ◽  
Eastern China ◽  
Threshold Level ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Oh Radicals ◽  
Chemical Production ◽  
The Past ◽  
Photochemical Production ◽  
Steady State Model

Abstract. PM2.5, a particulate matter with a diameter of 2.5 micrometers or less, is one of the major components of the air pollution in eastern China. In the past few years, China's government made strong efforts to reduce the PM2.5 pollutions. However, another important pollutant (ozone) becomes an important problem in eastern China. Ozone (O3) is produced by photochemistry, which requires solar radiation for the formation of O3. Under heavy PM2.5 pollution, the solar radiation is often depressed, and the photochemical production of O3 is prohibited. This study shows that during fall in eastern China, under heavy PM2.5 pollutions, there were often strong O3 photochemical productions, causing a co-occurrence of high PM2.5 and O3 concentrations. This co-occurrence of high PM2.5 and O3 is un-usual and is the main focus of this study. Recent measurements show that there were often high HONO surface concentrations in major Chinese mega cities, especially during daytime, with maximum concentrations ranging from 0.5 to 2 ppbv. It is also interesting to note that the high HONO concentrations were occurred during high aerosol concentration periods, suggesting that there were additional HONO surface sources in eastern China. Under the high daytime HONO concentrations, HONO can be photo-dissociated to be OH radicals, which enhance the photochemical production of O3. In order to study the above scientific issues, a radiative transfer model (TUV; Tropospheric Ultraviolet-Visible) is used in this study, and a chemical steady state model is established to calculate OH radical concentrations. The calculations show that by including the OH production of the photo-dissociated of HONO, the calculated OH concentrations are significantly higher than the values without including this production. For example, by including HONO production, the maximum of OH concentration under the high aerosol condition (AOD = 2.5) is similar to the value under low aerosol condition (AOD = 0.25) in the no-HONO case. This result suggests that even under the high aerosol condition, the chemical oxidizing process for O3 production can occurred, which explain the co-occurrence of high PM2.5 and high O3 in fall season in eastern China. However, the O3 concentrations were not significantly affected by the appearance of HONO in winter. This study shows that the seasonal variation of solar radiation plays important roles for controlling the OH production in winter. When the solar radiation is in a very low level in winter, it reaches the threshold level to prevent the OH chemical production, even by including the HONO production of OH. This study provides some important scientific highlights to better understand the O3 pollutions in eastern China.

scholarly journals Seasonal characteristics of fine particulate matter (PM) based on high-resolution time-of-flight aerosol mass spectrometric (HR-ToF-AMS) measurements at the HKUST Supersite in Hong Kong

2015 ◽  
Vol 15 (1) ◽  
pp. 37-53 ◽  
Author(s):  
Y. J. Li ◽  
B. P. Lee ◽  
L. Su ◽  
J. C. H. Fung ◽  
C.K. Chan
Keyword(s):  
Hong Kong ◽  
Organic Aerosols ◽  
Organic Aerosol ◽  
Resolution Time ◽  
Time Resolved ◽  
Air Mass ◽  
Aerosol Mass ◽  
Seasonal Characteristics ◽  
Autumn And Winter ◽  
Air Mass Origin

Abstract. Atmospheric particulate matter (PM) remains poorly understood due to the lack of comprehensive measurements at high time resolution for tracking its dynamic features and the lack of long-term observation for tracking its seasonal variability. Here, we present highly time-resolved and seasonal compositions and characteristics of non-refractory components in PM with a diameter less than 1 μm (NR-PM1) at a suburban site in Hong Kong. The measurements were made with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at the Hong Kong University of Science and Technology (HKUST) Air Quality Research Supersite for 4 months, with one in each season of the year. The average NR-PM1 concentration of ~ 15 μg m−3 is higher than those AMS measurements made in South Korea and Japan, but lower than those in North China, the Yangtze River Delta and the nearby Pearl River Delta. The seasonal dependence of the total NR-PM1 monthly averaged concentrations was small, but that of the fractions of the species in NR-PM1 was significant. Site characteristic plays an important role in the relative fractions of species in NR-PM1 and our results are generally consistent with measurements at other non-urban sites in this regard. Detailed analyses were conducted on the AMS data in the aspects of (1) species concentrations, (2) size distributions, (3) degree of oxygenation of organics, and (4) positive matrix factorization (PMF)-resolved organic factors in a seasonal context, as well as with air mass origin from back-trajectory analysis. Sulfate had the highest fraction in NR-PM1 (> 40%), and the surrogates of secondary organic species – semi-volatile oxygenated organic aerosol (SVOOA) and low-volatility oxygenated organic aerosol (LVOOA) – prevailed (~ 80%) in the organic portion of NR-PM1. Local contributions to the organic portion of NR-PM1 at this suburban site was strongly dependent on season. The hydrocarbon-like organic aerosol (HOA) factor related to local traffic emissions contributed > 10% to organic aerosols in spring and summer but only 6–7% in autumn and winter. The cooking organic aerosol (COA) factor contributed > 10% to organic aerosols in winter. With the aid of highly time-resolved data, diurnal patterns of the degree of oxygenation of organic aerosols were used to determine the sources and formation processes of the least understood organic portion of PM. The oxygen-to-carbon atomic ratio (O : C) and average carbon oxidation state OS C) showed little variation in autumn and winter, when the long-range transport of oxidized organics dominated, whereas they peaked in the afternoon in spring and summer, when locally produced secondary organic aerosol prevailed. Air mass origin, in contrast, had a strong influence on both NR-PM1 concentrations and the fractions of species in NR-PM1. The findings of the current study provide a better understanding of the role of air mass origin in the seasonal characteristics of the PM composition and the relative importance of local vs. transported organic aerosols in this region.

Numerical Simulation of Heat Transfer in Laminar Natural Convection of Mixed Newtonian-Non-Newtonian and Pure Non-Newtonian Nanofluids in a Square Enclosure

2021 ◽  
pp. 1-44
Author(s):  
Ajay Vallabh ◽  
P.S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Base Fluid ◽  
Volume Fraction ◽  
Numerical Study ◽  
Transfer Model ◽  
Nanoparticle Concentration ◽  
Left Wall ◽  
Square Enclosure ◽  
First Case

Abstract This paper presents a steady-state heat transfer model for the natural convection of mixed Newtonian-Non-Newtonian (Alumina-Water) and pure Non-Newtonian (Alumina-0.5 wt% Carboxymethyl Cellulose (CMC)/Water) nanofluids in a square enclosure with adiabatic horizontal walls and isothermal vertical walls, the left wall being hot and the right wall cold. In the first case the nanofluid changes its Newtonian character to Non-Newtonian past 2.78% volume fraction of the nanoparticles. In the second case the base fluid itself is Non-Newtonian and the nanofluid behaves as a pure Non-Newtonian fluid. The power-law viscosity model has been adopted for the non-Newtonian nanofluids. A finite-difference based numerical study with the Stream function-Vorticity-Temperature formulation has been carried out. The homogeneous flow model has been used for modelling the nanofluids. The present results have been extensively validated with earlier works. In Case I the results indicate that Alumina-Water nanofluid shows 4% enhancement in heat transfer at 2.78% nanoparticle concentration. Following that there is a sharp decline in heat transfer with respect to that in base fluid for nanoparticle volume fractions equal to and greater than 3%. In Case II Alumina-CMC/Water nanofluid shows 17% deterioration in heat transfer with respect to that in base fluid at 1.5% nanoparticle concentration. An enhancement in heat transfer is observed for increase in hot wall temperature at a fixed volume fraction of nanoparticles, for both types of nanofluid.

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