The characteristics of atmospheric brown carbon in Xi'an, inland China: sources, size distributions and optical properties

Abstract. To investigate the characteristics of atmospheric brown carbon (BrC) in the semiarid region of East Asia, PM2.5 and size-resolved particles in the urban atmosphere of Xi'an, inland China, during the winter and summer of 2017 were collected and analyzed for optical properties and chemical compositions. Methanol extracts (MeOH extracts) were more light-absorbing than water extracts (H2O extracts) in the optical wavelength of 300–600 nm and well correlated with nitrophenols, polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (r > 0.78). The light absorptions (absλ=365 nm) of H2O extracts and MeOH extracts in winter were 28±16 and 49±32 M m−1, respectively, which are about 10 times higher than those in summer, mainly due to the enhanced emissions from biomass burning for house heating. Water-extracted BrC predominately occurred in the fine mode (< 2.1 µm) during winter and summer, accounting for 81 % and 65 % of the total absorption of BrC, respectively. The light absorption and stable carbon isotope composition measurements showed an increasing ratio of absλ=365 nm-MeOH to absλ=550 nm-EC along with an enrichment of 13C in PM2.5 during the haze development, indicating an accumulation of secondarily formed BrC (e.g., nitrophenols) in the aerosol aging process. Positive matrix factorization (PMF) analysis showed that biomass burning, fossil fuel combustion, secondary formation, and fugitive dust are the major sources of BrC in the city, accounting for 55 %, 19 %, 16 %, and 10 % of the total BrC of PM2.5, respectively.

Download Full-text

The characteristics of atmospheric brown carbon in Xi'an, inland China: sources, size distributions and optical properties

10.5194/acp-2019-640 ◽

2019 ◽

Author(s):

Can Wu ◽

Gehui Wang ◽

Jin Li ◽

Jianjun Li ◽

Cong Cao ◽

...

Keyword(s):

Optical Properties ◽

Urban Atmosphere ◽

Chemical Compositions ◽

Size Distributions ◽

Brown Carbon ◽

Optical Wavelength ◽

Polycyclic Aromatic ◽

Fine Mode ◽

Semi Arid Region ◽

Oxygenated Pahs

Abstract. To investigate the characteristic of atmospheric brown carbon (BrC) in the semi-arid region of East Asia, PM2.5 and size-resolved particles in the urban atmosphere of Xi'an, inland China during the winter and summer of 2017 were collected and analyzed for optical properties and chemical compositions. Methanol extracts (MeOH-extracts) were more light-absorbing than water extracts (H2O- extracts) in the optical wavelength of 300–600 nm, and well correlated with nitrophenols, polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (R2 > 0.6). The light absorptions (absλ=365nm) of H2O- extracts and MeOH-extracts in winter were 28 ± 16 M/m and 49 ± 32 M/m, respectively, which are about 10 times higher than those in summer, mainly due to the enhanced emissions from biomass burning for house heating. Water extracted BrC predominately occurred in the fine mode (

Download Full-text

Measurement Report: Optical properties and sources of water-soluble brown carbon in Tianjin, North China: insights from organic molecular compositions

10.5194/acp-2021-1045 ◽

2022 ◽

Author(s):

Junjun Deng ◽

Hao Ma ◽

Xinfeng Wang ◽

Shujun Zhong ◽

Zhimin Zhang ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Light Absorption ◽

Radiative Forcing ◽

North China ◽

Water Soluble ◽

Formation Mechanisms ◽

Chemical Compositions ◽

Brown Carbon ◽

Near Ultraviolet

Abstract. Brown carbon (BrC) aerosols exert vital impacts on climate change and atmospheric photochemistry due to their light absorption in the wavelength range from near-ultraviolet (UV) to visible light. However, the optical properties and formation mechanisms of ambient BrC remain poorly understood, limiting the estimation of their radiative forcing. In the present study, fine aerosols (PM2.5) were collected during 2016–2017 on a day/night basis over urban Tianjin, a megacity in North China, to obtain seasonal and diurnal patterns of atmospheric water-soluble BrC. There were obvious seasonal but no evident diurnal variations in light absorption properties of BrC. In winter, BrC showed much stronger light absorbing ability since mass absorption efficiency at 365 nm (MAE365) (1.54 ± 0.33 m2 g−1), which was 1.8 times larger than that (0.84 ± 0.22 m2 g−1) in summer. Direct radiative effects by BrC absorption relative to black carbon in the UV range were 54.3 ± 16.9 % and 44.6 ± 13.9 %, respectively. In addition, five fluorescent components in BrC, including three humic-like fluorophores and two protein-like fluorophores were identified with excitation-emission matrix fluorescence spectrometry and parallel factor (PARAFAC) analysis. The lowly-oxygenated components contributed more to winter and nighttime samples, while more-oxygenated components increased in summer and daytime samples. The higher humification index (HIX) together with lower biological index (BIX) and fluorescence index (FI) suggest that the chemical compositions of BrC were associated with a high aromaticity degree in summer and daytime due to photobleaching. Fluorescent properties indicate that wintertime BrC were predominantly affected by primary emissions and fresh secondary organic aerosol (SOA), while summer ones were more influenced by aging processes. Results of source apportionments using organic molecular compositions of the same set of aerosols reveal that fossil fuel combustion and aging processes, primary bioaerosol emission, biomass burning, and biogenic and anthropogenic SOA formation were the main sources of BrC. Biomass burning contributed much larger to BrC in winter and at nighttime, while biogenic SOA contributed more in summer and at daytime. Especially, our study highlights that primary bioaerosol emission is an important source of BrC in urban Tianjin in summer.

Download Full-text

Chemical and optical properties of carbonaceous aerosols in Nanjing, eastern China: regionally transported biomass burning contribution

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-11213-2019 ◽

2019 ◽

Vol 19 (17) ◽

pp. 11213-11233 ◽

Cited By ~ 8

Author(s):

Xiaoyan Liu ◽

Yan-Lin Zhang ◽

Yiran Peng ◽

Lulu Xu ◽

Chunmao Zhu ◽

...

Keyword(s):

Optical Properties ◽

Organic Carbon ◽

Solar Energy ◽

Energy Absorption ◽

Biomass Burning ◽

Eastern China ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Southeastern China ◽

Brown Carbon

Abstract. Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the biomass burning impacts were studied during wintertime in a megacity of Nanjing, eastern China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss-K+) was found during the studied period with the concentration ranges of 22.4–1476 ng m−3, 2.1–56.2 ng m−3, 1.4–32.2 ng m−3 and 0.2–3.8 µg m−3, respectively. The significant contribution of biomass burning to water-soluble organic carbon (WSOC; 22.3±9.9 %) and organic carbon (OC; 20.9±9.3 %) was observed in this study. Backward air mass origin analysis, potential emission sensitivity of elemental carbon (EC) and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from southeastern China. The characteristic mass ratio maps of lev∕man and lev∕nss-K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p < 0.01) between biomass burning tracers (such as lev) and light absorption coefficient (babs) for water-soluble brown carbon (BrC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon and EC was estimated by a calculation based on measured light-absorbing parameters and a simulation based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300–400 nm) was 0.8±0.4 (0.2–2.3) W m−2 (figures in parentheses represent the variation range of each parameter) from the calculation and 1.2±0.5 (0.3–1.9) W m−2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20 %–30 % of the total absorption of EC aerosols. The solar energy absorption of water-soluble BrC due to biomass burning was estimated as 0.2±0.1 (0.0–0.9) W m−2, considering the biomass burning contribution to carbonaceous aerosols. Potential source contribution function model simulations showed that the solar energy absorption induced by water-soluble BrC and EC aerosols was mostly due to the regionally transported carbonaceous aerosols from source regions such as southeastern China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere.

Download Full-text

Remote sensing of soot carbon – Part 1: Distinguishing different absorbing aerosol species

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-13607-2015 ◽

2015 ◽

Vol 15 (9) ◽

pp. 13607-13656 ◽

Cited By ~ 4

Author(s):

G. L. Schuster ◽

O. Dubovik ◽

A. Arola

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Iron Oxide ◽

South America ◽

Biomass Burning ◽

Southern Africa ◽

Refractive Indices ◽

Carbonaceous Aerosols ◽

Fine Mode ◽

Soot Carbon

Abstract. We describe a method of using the aerosol robotic network (AERONET) size distributions and complex refractive indices to retrieve the relative proportion of carbonaceous aerosols and iron oxide minerals. We assume that soot carbon has a spectrally flat refractive index, and that enhanced imaginary indices at the 440 nm wavelength are caused by brown carbon or hematite. Carbonaceous aerosols can be separated from dust in imaginary refractive index space because 95% of biomass burning aerosols have imaginary indices greater than 0.0042 at the 675–1020 nm wavelengths, and 95% of dust has imaginary refractive indices of less than 0.0042 at those wavelengths. However, mixtures of these two types of particles can not be unambiguously partitioned on the basis of optical properties alone, so we also separate these particles by size. Regional and seasonal results are consistent with expectations. Monthly climatologies of fine mode soot carbon are less than 1.0% by volume for West Africa and the Middle East, but the southern Africa and South America biomass burning sites have peak values of 3.0 and 1.7%. Monthly-averaged fine mode brown carbon volume fractions have a peak value of 5.8% for West Africa, 2.1% for the Middle East, 3.7% for southern Africa, and 5.7% for South America. Monthly climatologies of iron oxide volume fractions show little seasonal variability, and range from about 1.1 to 1.7% for coarse mode aerosols in all four study regions. Finally, our sensitivity study indicates that the soot carbon retrieval is not sensitive to the component refractive indices or densities assumed for carbonaceous and iron oxide aerosols, and differs by only 15.4% when these parameters are altered from our chosen baseline values. The associated soot carbon absorption aerosol optical depth (AAOD) does not vary at all when these parameters are altered, however, because the retrieval is constrained by the AERONET optical properties.

Download Full-text

Exploring the observational constraints on the simulation of brown carbon

10.5194/acp-2017-655 ◽

2017 ◽

Author(s):

Xuan Wang ◽

Colette L. Heald ◽

Jiumeng Liu ◽

Rodney J. Weber ◽

Pedro Campuzano-Jost ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Transport Model ◽

Model Simulation ◽

Radiative Transfer Model ◽

Transfer Model ◽

Observational Constraints ◽

Radiative Effect ◽

Brown Carbon ◽

Direct Measurements

Abstract. Organic aerosols (OA) that strongly absorbs solar radiation in the near-UV are referred to as brown carbon (BrC). However the sources, evolution, and optical properties of BrC remain highly uncertain, and contribute significantly to uncertainty in the estimate of the global direct radiative effect (DRE) of aerosols. Previous modeling studies of BrC optical properties and DRE have been unable to fully evaluate model performance due to the lack of direct measurements of BrC absorption. In this study, we develop a global model simulation (GEOS-Chem) of BrC and test it against BrC absorption measurements from two aircraft campaigns in the continental U.S. (SEAC4RS and DC3). To our knowledge, this is the first study to compare simulated BrC absorption with direct ambient measurements. We show that the BrC absorption properties from biomass burning estimated based on previous laboratory measurements overestimate the aircraft measurements of ambient BrC absorption. In addition, applying a photochemical scheme to simulate bleaching/degradation of BrC improves model skill. The airborne observations are consistent with a mass absorption coefficient (MAC) of freshly emitted biomass burning OA of 0.57 m2 g−1 at 365 nm with an absorption Ångström exponents (AAE) = 3.1 for 300 & 600 wavelengths pair, coupled with a 1 day whitening e-folding time. Using the GEOS-Chem chemical transport model integrated with the RRTMG radiative transfer model, we estimate that the top-of-atmosphere all-sky direct radiative effect (DRE) of OA is −0.350 Wm−2, 10 % higher than that without consideration of BrC absorption. Therefore, our best estimate of the absorption DRE of BrC is +0.042 Wm−2. We suggest that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical whitening.

Download Full-text

Molecular markers of biomass burning and primary biological aerosols in urban Beijing: size distribution and seasonal variation

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-3623-2020 ◽

2020 ◽

Vol 20 (6) ◽

pp. 3623-3644 ◽

Cited By ~ 3

Author(s):

Shaofeng Xu ◽

Lujie Ren ◽

Yunchao Lang ◽

Shengjie Hou ◽

Hong Ren ◽

...

Keyword(s):

Molecular Markers ◽

Biomass Burning ◽

Aerosol Particles ◽

Fungal Spores ◽

Chemical Compositions ◽

Plant Debris ◽

Urban Aerosols ◽

Biological Aerosols ◽

Coarse Mode ◽

Fine Mode

Abstract. Biomass burning and primary biological aerosol particles account for an important part of urban aerosols. Floods of studies have been conducted on the chemical compositions of fine aerosols (PM2.5) in megacities where the haze pollution is one of the severe environmental issues in China. However, little is known about their size distributions in atmospheric aerosols in the urban boundary layer. Here, size-segregated aerosol samples were collected in Beijing during haze and clear days from April 2017 to January 2018. Three anhydrosugars, six primary saccharides and four sugar alcohols in these samples were identified and quantified by gas chromatography/mass spectrometry (GC/MS). Higher concentrations of a biomass burning tracer, levoglucosan, were detected in autumn and winter than in other seasons. Sucrose, glucose, fructose, mannitol and arabitol were more abundant in the bloom and glowing seasons. A particularly high level of trehalose was found in spring, which was largely associated with the Asian dust outflows. Anhydrosugars, xylose, maltose, inositol and erythritol are mainly present in the fine mode (<2.1 µm), while the others showed the coarse-mode preference. The concentrations of measured tracers of biomass burning particles and primary biological particles in the haze events were higher than those in the non-hazy days, with enrichment factors of 2–10. Geometric mean diameters (GMDs) of molecular markers of biomass burning and primary biological aerosols showed that there was no significant difference in the coarse mode (>2.1 µm) between the haze and non-haze samples, while a size shift towards large particles and large GMDs in the fine fraction (<2.1 µm) was detected during the hazy days, which highlights that the stable meteorological conditions with high relative humidity in urban Beijing may favor the condensation of organics onto coarse particles.The contributions of reconstructed primary organic carbon (POC) by tracer-based methods from plant debris, fungal spores and biomass burning to aerosol OC in the total-mode particles were in the ranges of 0.09 %–0.30 % (on average 0.21 %), 0.13 %–1.0 % (0.38 %) and 1.2 %–7.5 % (4.5 %), respectively. This study demonstrates that the contribution of biomass burning was significant in Beijing throughout the whole year with the predominance in the fine mode, while the contributions of plant debris and fungal spores dominated in spring and summer in the coarse mode, especially in sizes >5.8 µm. Our observations demonstrate that the sources, abundance and chemical composition of urban aerosol particles are strongly size dependent in Beijing, which is important to better understand the environmental and health effects of urban aerosols and should be considered in air quality and climate models.

Download Full-text