Aerosol optical properties and mixing state of black carbon in the Pearl River Delta, China

Tan, Haobo; Liu, Li; Fan, Saijun; Li, Fēi; Yin, Yan; Cai, Mingfu; Chan, Pak Wai

doi:10.1016/j.atmosenv.2016.02.003

Cited by 48 publications

(30 citation statements)

References 61 publications

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“…The conversion between these two types of diameters involves the knowledge of particle density and morphology (drag force). A recent closure study on BC mixing state in the PRD region sug- gests σ abs is dominated by coated soot particles in the range of ∼300-400 nm (Tan et al, 2016). Considering the dominant BC core distribution measured with SP2 (110 nm), the upper limit of E abs in the PRD is roughly estimated as ∼ 2 for the clear shell scenario (Fig.…”

Section: Mie-modeled Light Absorption Enhancement Factor (E Abs )mentioning

confidence: 99%

Quantifying black carbon light absorption enhancement with a novel statistical approach

Wang

2018

Atmos. Chem. Phys.

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Abstract. Black carbon (BC) particles in the atmosphere can absorb more light when coated by non-absorbing or weakly absorbing materials during atmospheric aging, due to the lensing effect. In this study, the light absorption enhancement factor, E abs , was quantified using a 1-year measurement of mass absorption efficiency (MAE) in the Pearl River Delta region (PRD). A new approach for calculating primary MAE (MAE p ), the key for E abs estimation, is demonstrated using the minimum R squared (MRS) method, exploring the inherent source independency between BC and its coating materials. A unique feature of E abs estimation with the MRS approach is its insensitivity to systematic biases in elemental carbon (EC) and σ abs measurements. The annual average E abs550 is found to be 1.50±0.48 (±1 SD) in the PRD region, exhibiting a clear seasonal pattern with higher values in summer and lower in winter. Elevated E abs in the summertime is likely associated with aged air masses, predominantly of marine origin, along with long-range transport of biomassburning-influenced air masses from Southeast Asia. Coreshell Mie simulations along with measured E abs and absorption Ångström exponent (AAE) constraints suggest that in the PRD, the coating materials are unlikely to be dominated by brown carbon and the coating thickness is higher in the rainy season than in the dry season.

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Section: Mie-modeled Light Absorption Enhancement Factor (E Abs )mentioning

confidence: 99%

Quantifying black carbon light absorption enhancement with a novel statistical approach

Wang

2018

Atmos. Chem. Phys.

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“…Man and Shih (2001) Cheng et al (2008) presented the 1-month record of aerosol optical measurements with related chemical apportionment at Xinken in the PRD region and reported a relatively low SSA at this polluted rural site. Mixing states of light-absorbing aerosols were also investigated using optical closure experiments during the campaign (Cheng et al, 2006b;Tan et al, 2016). However, long-term observations of several key aerosol optical properties (including wavelength dependencies of light scattering and absorption SSA), and studies on the relationships between optical properties and particle size as well as their quantitative linkage to multi-scale transport) have been limited in Hong Kong over the past decade.…”

Section: Introductionmentioning

confidence: 99%

Observations of aerosol optical properties at a coastal site in Hong Kong, South China

et al. 2017

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Abstract. Temporal variations in aerosol optical properties were investigated at a coastal station in Hong Kong based on the field observation from February 2012 to February 2015. At 550 nm, the average light-scattering (151 ± 100 Mm −1 ) and absorption coefficients (8.3 ± 6.1 Mm −1 ) were lower than most of other rural sites in eastern China, while the single-scattering albedo (SSA = 0.93 ± 0.05) was relatively higher compared with other rural sites in the Pearl River Delta (PRD) region. Correlation analysis confirmed that the darkest aerosols were smaller in particle size and showed strong scattering wavelength dependencies, indicating possible sources from fresh emissions close to the measurement site. Particles with D p of 200-800 nm were less in number, yet contributed the most to the light-scattering coefficients among submicron particles. In summer, both BC / CO and SO 2 / BC peaked, indicating the impact of nearby combustion sources on this site. Multi-year backward Lagrangian particle dispersion modeling (LPDM) and potential source contribution (PSC) analysis revealed that these particles were mainly from the air masses that moved southward over Shenzhen and urban Hong Kong and the polluted marine air containing ship exhausts. These fresh emission sources led to low SSA during summer months. For winter and autumn months, contrarily, BC / CO and SO 2 / BC were relatively low, showing that the site was more under influence of well-mixed air masses from long-range transport including from South China, East China coastal regions, and aged aerosol transported over the Pacific Ocean and Taiwan, causing stronger abilities of light extinction and larger variability of aerosol optical properties. Our results showed that ship emissions in the vicinity of Hong Kong could have visible impact on the light-scattering and absorption abilities as well as SSA at Hok Tsui.

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“…In comparison, the absorption coefficient of EP-5 (468.7 Mm −1 ) was about 94.7 times higher than that of EP-4 (1.3 Mm 1 ), more than 8 times the BC ratio. It was supposed that BC was internally mixed with other aerosols in the EP-5, which led to the considerable increase in absorption coefficient (Tan et al, 2016). However, models estimated an enhancement of BC forcing up to a factor of 2.9 when BC is internally mixed with other aerosols, compared with externally mixed scenarios (Jacobson, 2001), which was much lower than this case.…”

Section: Optical Properties Related To Morphological Types Of Aerosolsmentioning

confidence: 64%

“…Our observations were agreement with the previous studies reported by (Wang et al, 2009b;Xia et al, 2006), which shows that aerosol particles under hazy weather conditions generate a positive heating effect on the atmosphere. During the foggy days of EP-3 episode, the high PM 10 concentration and AOD caused a significant increase in scattering coefficient (Tan et al, 2016). Furthermore, metal-bearing particles and soot were internally associated with some coatings, including Srich, N-rich and K-rich particles.…”

Section: Optical Properties Related To Morphological Types Of Aerosolsmentioning

confidence: 98%

“…On the other hand, under the conditions of high atmospheric relative humidity (RH), the initially hydrophobic soot particles can become associated with hygroscopic materials, leading to increased scattering due to particle growth. In an extreme case, the coating material can cause the absorbing fractal soot to collapse, potentially changing optical behaviour, which further complicates this picture Langridge et al, 2012;Lei et al, 2014;Tan et al, 2016). Such changes cause both positive and negative effects on the interplay between the direct and indirect aerosol effects, making overall prediction of the radiative forcing difficult.…”

Section: Introductionmentioning

confidence: 99%

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Real-time aerosol optical properties, morphology and mixing states under clear, haze and fog episodes in the summer of urban Beijing

et al. 2017

Atmos. Chem. Phys.

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Abstract. Elucidating the relationship between characteristics of aerosol particles and optical absorption is important to deepen the understanding of atmospheric chemistry. Aerosol particles play significant roles in climate forcing via their optical absorption properties. However, the relationship between characteristics of aerosol particles and optical absorption remains poorly understood. Aerosol optical properties and morphologies were measured by a transmission electron microscope (TEM), cavity ring-down spectrometer (CRDS), a nephelometer and an Aethalometer in a urban site of Beijing from 24 May to 22 June. Five episodes were categorized according to the meteorological conditions and composition. The results showed that the clear episode (EP-2 and EP-4) featured as the low aerosol optical depth (AOD = 0.72) and fewer pollutants compared with haze (1.14) and fog (2.92) episodes and the particles are mostly externally mixed. The high Ångström exponent (> 2.0) suggests that coarse particles were scarcely observed in EP-2 due to the washout of a previous heavy rain, whereas they were widespread in EP-4 (Ångström exponent = 0.04), which had some mineral particles introduced from the north. In contrast, industry-induced haze (EP-1) and biomass-burning-induced haze (EP-5) were both affected by the south air mass. Compared with the EP-2 and EP-4, the AOD values and the size distribution of particles during EP-1 and EP-5 were much greater because of relatively high particle concentrations. All of the particles were classified into nine categories, i.e. S-rich, N-rich, mineral, K-rich, soot, tar ball, organic, metal and fly ash, on the basis of TEM analysis. In contrast to the EP-1, a large fraction of soot, which sticks to KCl, sulfate or nitrate particles, was detected during EP-5. Additionally, evident enhancement of light absorption was observed during the EP-5, which was mainly ascribed to both black carbon (BC) acceleration and other absorbing substances. However, soot was found mostly internally mixed with sulfate and nitrate during a soot fog episode (EP-3), resulting in evident enhancement of light absorption. The larger size distribution was likely to be caused by both hygroscopic growth and collision between particles during the aging. About 28 % of particles were internally mixed during the foggy days, which favoured the light absorption. The comparison of all the episodes provides a deeper insight into how mixing states influence the aerosol extinction properties and also a clue as to how to control air pollution in the crop burning seasons.

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Aerosol optical properties and mixing state of black carbon in the Pearl River Delta, China

Cited by 48 publications

References 61 publications

Quantifying black carbon light absorption enhancement with a novel statistical approach

Quantifying black carbon light absorption enhancement with a novel statistical approach

Observations of aerosol optical properties at a coastal site in Hong Kong, South China

Real-time aerosol optical properties, morphology and mixing states under clear, haze and fog episodes in the summer of urban Beijing

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