First Chemical Characterization of Refractory Black Carbon Aerosols and Associated Coatings over the Tibetan Plateau (4730 m a.s.l)

Wang, Jun Feng; Zhang, Qi; Chen, Mindong; Collier, Sonya; Zhou, Shan; Ge, Xinlei; Xu, Jianzhong; Shi, Jun; Xie, Conghui; Hu, Jianlin; Ge, Shemin; Sun, Yele; Coe, Hugh

doi:10.1021/acs.est.7b03973

Cited by 65 publications

(54 citation statements)

References 95 publications

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“…Under pollution conditions, RBC was higher than that under clean conditions, with an average value of 5.0. RBC in Beijing even exceeded 10.0 in some extremely severe pollution events, which is close to observations of remote sites (Wang et al, 2017;Massoli et al, 2015) and aged particles (Cappa et al, 2012 Figure 12 shows the evolution of RBC, the size distribution of number concentrations, and the GMD along the transport pathway from the source region to…”

Section: Evolution Of Aerosol Properties In Beijing During Haze Episodessupporting

confidence: 80%

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: Roles of regional transport and heterogeneous reactions

Du¹,

Li²,

Chen³

et al. 2018

Preprint

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Abstract. Regional transport and heterogeneous reactions played crucial roles in haze formation over a megacity cluster centered on Beijing. In this study, the updated Nested Air Quality Prediction Model System (NAQPMS) and the HYSPLIT Lagrangian trajectory model were employed to investigate the evolution of aerosols &#8211; in terms of the number concentration, size distribution, and aging degree &#8211; in Beijing during six haze episodes between November 15 and December 15, 2016, as part of the Air Pollution and Human Health&#8211;Beijing (APHH-Beijing) winter campaign of 2016. The model exhibited reasonable performance not only for mass concentrations of PM2.5 and its components in Beijing but also for the number concentration, size distribution, and aging degree. We discovered that regional transport played a nonnegligible role in haze episodes, with contributions of 14&#8201;%&#8211;31&#8201;% to the surface PM2.5 mass concentration. The contribution of regional transport to secondary inorganic aerosols was larger than that of regional transport to primary aerosols (30&#8201;%&#8211;63&#8201;% vs. 3&#8201;%&#8211;12&#8201;%). The chemical transformation of SO2 in the transport pathway from source regions to Beijing was the major form of SO42&#8722; regional transport. We also found that sulfate formed outside Beijing from SO2 that was emitted in Beijing; this sulfate was then blown back to Beijing and considerably influenced haze formation. In the transport pathway, aerosols underwent aging, which altered the mass ratio of coating to black carbon (RBC) and the size distribution of number concentrations. During the episodes, the geometric mean diameter (GMD) increased from less than 100&#8201;nm at the initial site to approximately 120&#8201;nm at the final site (Beijing), and RBC increased from 2&#8211;4 to 4&#8211;8. These changes would affect regional radiation and climate. In haze episodes with high humidity, the average contributions of gas and aqueous chemistry, heterogeneous chemistry, and primary sulfate emission were comparable. Primary emissions had the greatest impact under light to moderate pollution levels, whereas heterogeneous chemistry had a stronger effect under high pollution levels.

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Section: Evolution Of Aerosol Properties In Beijing During Haze Episodessupporting

confidence: 80%

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: Roles of regional transport and heterogeneous reactions

Du¹,

Li²,

Chen³

et al. 2018

Preprint

Self Cite

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“…7). We propose the increased underestimation during polluted conditions is likely due to enhanced condensation of secondary hygroscopic compounds (e.g., ni- trate, sulfate, SOA) on preexisting aerosols at lower temperature and or hydrophilic SOA formation under higher relative humidity at nighttime (Wu et al, 2008;Wang et al, 2016;An et al, 2019). However, such a condensation effect during nighttime is less significant (indicated by the smaller disparity between κ chem and κ gf ) than the aging effect caused by aerosol photochemical processes around noontime (J. F. .…”

Section: Aerosols Aging and Source Effects Indicated By Diurnal Cyclementioning

confidence: 97%

“…The particle mobility diameter was estimated by dividing the vacuum aerodynamic diameter from the AMS measurements by particle density. Because the uncertainty caused by the fixed density across the size range is negligible (Wang et al, 2016), here, the particle density is assumed to be 1600 kg m −3 (Zamora et al, 2019). AMS positive matrix factorization (PMF) with the PMF2.exe (v4.2) method was performed to identify various factors of organic aerosols.…”

Section: Introductionmentioning

confidence: 99%

Contrasting size-resolved hygroscopicity of fine particles derived by HTDMA and HR-ToF-AMS measurements between summer and winter in Beijing: the impacts of aerosol aging and local emissions

et al. 2020

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Abstract. The effects of aerosols on visibility through scattering and absorption of light and on climate through altering cloud droplet concentration are closely associated with their hygroscopic properties. Here, based on field campaigns in winter and summer in Beijing, we compare the size-resolved hygroscopic parameter (κgf) of ambient fine particles derived by an HTDMA (hygroscopic tandem differential mobility analyzer) to that (denoted as κchem) calculated by an HR-ToF-AMS (high-resolution time-of-flight aerosol mass spectrometer) measurements using a simple rule with the hypothesis of uniform internal mixing of aerosol particles. We mainly focus on contrasting the disparity of κgf and κchem between summer and winter to reveal the impact of atmospheric processes/emission sources on aerosol hygroscopicity and to evaluate the uncertainty in estimating particle hygroscopicity with the hypothesis. We show that, in summer, the κchem for 110, 150, and 200 nm particles was on average ∼10 %–12 % lower than κgf, with the greatest difference between the values observed around noontime when aerosols experience rapid photochemical aging. In winter, no apparent disparity between κchem and κgf is observed for those >100 nm particles around noontime, but the κchem is much higher than κgf in the late afternoon when ambient aerosols are greatly influenced by local traffic and cooking sources. By comparing with the observation from the other two sites (Xingtai, Hebei and Xinzhou, Shanxi) of north China, we verify that atmospheric photochemical aging of aerosols enhances their hygroscopicity and leads to 10 %–20 % underestimation in κchem if using the uniform internal mixing assumption. The effect is found more significant for these >100 nm particles observed in remote or clean regions. The lower κchem likely resulted from multiple impacts of inappropriate application of the density and hygroscopic parameter of organic aerosols in the calculation, as well as influences from chemical interaction between organic and inorganic compounds on the overall hygroscopicity of mixed particles. We also find that local/regional primary emissions, which result in a large number of externally mixed BC (black carbon) and POA (primary organic aerosol) in urban Beijing during traffic rush hour time, cause a 20 %–40 % overestimation of the hygroscopic parameter. This is largely due to an inappropriate use of density of the BC particles that is closely associated with its morphology or the degree of its aging. The results show that the calculation can be improved by applying an effective density of fresh BC (0.25–0.45 g cm−3) in the mixing rule assumption. Our study suggests that it is critical to measure the effective density and morphology of ambient BC, in particular in those regions with influences of rapid secondary conversion/aging processes and local sources, so as to accurately parameterize the effect of BC aging on particle hygroscopicity.

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“…The chemical composition of black-carbon-containing particles, including the refractory BC and coating compositions, is measured by a soot particle mass spectrometer (SP-AMS) (Onasch et al, 2012a;Wang et al, 2017). The results from SP-AMS measurement during the APHH (Air Pollution and Human Health) project are detailed in Wang et al (2019).…”

Section: Bc Chemical Compositionmentioning

confidence: 99%

Contrasting physical properties of black carbon in urban Beijing between winter and summer

et al. 2019

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Abstract. Black carbon (BC) is known to have major impacts on both human health and climate. The populated megacity represents the most complex anthropogenic BC emissions where the sources and related impacts are very uncertain. This study provides source attribution and characterization of BC in the Beijing urban environment during the joint UK–China APHH (Air Pollution and Human Health) project, in both winter (November–December 2016) and summer (May–June 2017). The size-resolved mixing state of BC-containing particles was characterized by a single-particle soot photometer (SP2) and their mass spectra was measured by a soot particle aerosol mass spectrometer (SP-AMS). The refractory BC (rBC) mass loading was around a factor of 2 higher in winter relative to summer, and more variable coatings were present, likely as a result of additional surface emissions from the residential sector and favourable condensation in the cold season. The characteristics of the BC were relatively independent of air mass direction in summer, whereas in winter air masses from the Northern Plateau were considerably cleaner and contained less-coated and smaller BC, but the BC from the Southern Plateau had the largest core size and coatings. We compare two online source apportionment methods using simultaneous measurements made by the SP2, which measures physical properties of BC, and the chemical approach using the positive matrix factorization (PMF) of mass spectra from the SP-AMS for the first time. A method is proposed to isolate the BC from the transportation sector using a mode of small BC particles (core diameter Dc<0.18 µm and coating thickness ct < 50 nm). This mode of BC highly correlated with NOx concentration in both seasons (∼14 ng m−3 BC ppb−1 NOx) and corresponded with the morning traffic rush hour, contributing about 30 % and 40 % of the total rBC mass (35 % and 55 % in number) in winter and summer respectively. The BC from coal burning or biomass burning was characterized by moderate coatings (ct = 50–200 nm) contributing ∼20 %–25 % of rBC mass. Large uncoated BC particles (Dc>0.18 µm and ct < 50 nm) were more likely to be contributed by coal combustion, as these particles were not present in urban London. This mode was present in Beijing in both winter (∼30 %–40 % rBC mass) and summer (∼40 % rBC mass) but may be dominated by the residential and industrial sector respectively. The contribution of BC thickly coated with secondary species (ct > 200 nm) to the total rBC mass increased with pollution level in winter but was minor in summer. These large BC particles importantly enhanced the absorption efficiency at high pollution levels – in winter when PM1 > 100 µg m−3 or BC > 2 µg m−3, the absorption efficiency of BC increased by 25 %–70 %. The reduction of emissions of these large BC particles and the precursors of the associated secondary coating will be an effective way of mitigating the heating effect of BC in urban environments.

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First Chemical Characterization of Refractory Black Carbon Aerosols and Associated Coatings over the Tibetan Plateau (4730 m a.s.l)

Cited by 65 publications

References 95 publications

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: Roles of regional transport and heterogeneous reactions

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: Roles of regional transport and heterogeneous reactions

Contrasting size-resolved hygroscopicity of fine particles derived by HTDMA and HR-ToF-AMS measurements between summer and winter in Beijing: the impacts of aerosol aging and local emissions

Contrasting physical properties of black carbon in urban Beijing between winter and summer

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