Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN): integrated analysis and intensive winter campaign 2018

High-RH-favored multiphase reactions can significantly change the chemical composition of fine particles and thereby modify their physicochemical properties.

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McFAN experiment: An integrated analysis of the multiphase chemistry experiment in Fogs and Aerosols in the North China Plain

10.5194/egusphere-egu2020-16757 ◽

2020 ◽

Author(s):

Hang Su ◽

Nan Ma ◽

Yele Sun ◽

Jiangchuan Tao ◽

Pingqing Fu ◽

...

Keyword(s):

North China Plain ◽

North China ◽

Winter Season ◽

Direct Determination ◽

Organic Aerosol ◽

Integrated Analysis ◽

The North ◽

The North China Plain ◽

The Impact ◽

Chemistry Experiment

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physical-chemical mechanisms leading to the haze formation with a focus on the contributions of multiphase processes in aerosol and fogs. We integrated multiple platform observations with regional and box models to identify the key oxidation process producing sulfate, nitrate and secondary organic aerosols, and their impact. A new environmental chamber was deployed to conduct kinetic experiments with real atmospheric compositions in comparison to literature kinetic data from laboratory studies. The experiments were carried out for multiple years since 2017 at the Gucheng site in the center of polluted areas and have performed experiments in the winter season. The location of the site minimizes fast transition between clean and polluted air masses (e.g., in Beijing), and helps to maintain a pollution regime representative for the North China Plain. The multi-year consecutive experiments documented the trend of PM2.5 pollution and corresponding change of aerosol physical and chemical properties, and allowed to investigate newly proposed mechanisms. The preliminary results show new proofs of the key role of aqueous phase reactions in regulating the aerosol compositions during haze events.Reference:Zheng et al., Exploring the severe winter haze in Beijing: the impact of synoptic weather, regional transport and heterogeneous reactions. Atmospheric Chemistry and Physics 15, 2969-2983 (2015).Cheng et al., Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China. Science Advances 2,&#160; (2016).Li et al., Multifactor colorimetric analysis on pH-indicator papers: an optimized approach for direct determination of ambient aerosol pH. Atmos. Meas. Tech. Discuss. 2019, 1-19 (2019).Kuang et al., Distinct diurnal variation of organic aerosol hygroscopicity and its relationship with oxygenated organic aerosol. Atmos. Chem. Phys. Discuss. 2019, 1-33 (2019).&#160;

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Summertime fine particulate nitrate pollution in the North China Plain: Increasing trends, formation mechanisms, and implications for control policy

10.5194/acp-2018-89 ◽

2018 ◽

Author(s):

Liang Wen ◽

Likun Xue ◽

Xinfeng Wang ◽

Caihong Xu ◽

Tianshu Chen ◽

...

Keyword(s):

North China Plain ◽

North China ◽

Fine Particles ◽

Nitrate Pollution ◽

Effective Control ◽

Formation Mechanisms ◽

The North ◽

The North China Plain ◽

Holistic Understanding ◽

Nitrate Aerosol

Abstract. Nitrate aerosol composes a significant fraction of fine particles and plays a key role in regional air quality and climate. To obtain a holistic understanding of the nitrate pollution and its formation mechanisms over the North China Plain (NCP) – the most industrialized and polluted region in northern China, intensive field observations were conducted at three sites during summertime in 2014–2015. The measurement sites include the downtown and downwind of Ji'nan, the capital city of Shandong Province, as well as the peak of NCP – Mt. Tai (1534 m a.s.l.), and hence cover representative urban, rural and remote areas of the region. Elevated nitrate concentrations were observed at all three sites despite distinct temporal and spatial variations. The nitrate / PM2.5 and nitrate / sulfate ratios have significantly increased in Ji'nan (2005–2015) and at Mt. Tai (from 2007 to 2014), indicating the worsening situation of regional nitrate pollution. A multi-phase chemical box model (RACM/CAPRAM) was deployed and constrained by observations to elucidate the nitrate formation mechanisms. The principal formation route is the partitioning of gaseous HNO3 to aerosol phase at daytime, whilst the nocturnal nitrate formation is dominated by the heterogeneous hydrolysis of N2O5. The daytime nitrate production in the NCP region is mainly limited by the availability of NO2 and to a lesser extent O3 and NH3, and the nighttime formation is controlled by both NO2 and O3. NH3 prompts significantly the nitrate formation at daytime but plays a slightly negative role in the nighttime. Our analyses suggest that controlling NOx and O3 is an efficient way at the moment to mitigate nitrate pollution in the NCP region, where NH3 is usually in excess in summer. This study provides observational evidence of rising trend of nitrate aerosol as well as scientific support for formulating effective control strategies for regional haze in China.

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On the difference of aerosol hygroscopicity between high and low RH environment in the North China Plain

10.5194/egusphere-egu21-13951 ◽

2021 ◽

Author(s):

Jingnan Shi ◽

Juan Hong ◽

Nan Ma ◽

Qingwei Luo ◽

Hanbing Xu ◽

...

Keyword(s):

Chemical Composition ◽

North China Plain ◽

North China ◽

Experimental Period ◽

Formation Mechanisms ◽

Large Contribution ◽

The North ◽

The North China Plain ◽

The Difference ◽

Aerosol Hygroscopicity

Simultaneous measurements of aerosol hygroscopicity and chemical composition were performed at a suburban site in the North China Plain in winter 2018 using a self-assembled hygroscopic tandem differential mobility analyzer (H-TDMA) and a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM), respectively. During the experimental period, aerosol particles usually show an external mixture in terms of hygroscopicity, with a less hygroscopic particles mode (LH) and a more hygroscopic mode (MH). The average ensemble mean hygroscopicity parameter (&#954;mean) are 0.16, 0.18, 0.16, and 0.15 for 60, 100, 150, and 200 nm particles, respectively. Two episodes with different RH/T conditions and secondary aerosol formations are distinguished. Higher aerosol hygroscopicity is observed for all measured sizes in the high RH episode (HRH) than in the low RH episode (LRH). In LRH, &#954; decreases as the particle size increases, which may be explained by the large contribution of non- or less-hygroscopic primary compounds in large particles due to the enhanced domestic heating emissions at low temperature. The number fraction of LH mode at 200 nm even exceeds 50%. Closure analysis is carried out between the HTDMA-measured &#954; and the ACSM-derived hygroscopicity using different approximations for the hygroscopic parameters of organic compounds (&#954;org). The results indicate that &#954;org is less sensitive towards the variation of its oxidation level under HRH conditions but has a stronger O: C-dependency under LRH conditions. The difference in the chemical composition and their corresponding physical properties under different RH/T conditions reflects potentially different formation mechanisms of secondary organic aerosols at those two distinct episodes.

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Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-2525-2014 ◽

2014 ◽

Vol 14 (5) ◽

pp. 2525-2539 ◽

Cited By ~ 78

Author(s):

H. J. Liu ◽

C. S. Zhao ◽

B. Nekat ◽

N. Ma ◽

A. Wiedensohler ◽

...

Keyword(s):

Chemical Composition ◽

Ultrafine Particles ◽

Mass Fraction ◽

North China Plain ◽

North China ◽

The North ◽

The North China Plain ◽

Mass Fractions ◽

Particulate Mass ◽

Aerosol Hygroscopicity

Abstract. Hygroscopic growth of aerosol particles is of significant importance in quantifying the aerosol radiative effect in the atmosphere. In this study, hygroscopic properties of ambient particles are investigated based on particle chemical composition at a suburban site in the North China Plain during the HaChi campaign (Haze in China) in summer 2009. The size-segregated aerosol particulate mass concentration as well as the particle components such as inorganic ions, organic carbon and water-soluble organic carbon (WSOC) are identified from aerosol particle samples collected with a ten-stage impactor. An iterative algorithm is developed to evaluate the hygroscopicity parameter κ from the measured chemical composition of particles. During the HaChi summer campaign, almost half of the mass concentration of particles between 150 nm and 1 μm is contributed by inorganic species. Organic matter (OM) is abundant in ultrafine particles, and 77% of the particulate mass with diameter (Dp) of around 30 nm is composed of OM. A large fraction of coarse particle mass is undetermined and is assumed to be insoluble mineral dust and liquid water. The campaign's average size distribution of κ values shows three distinct modes: a less hygroscopic mode (Dp < 150 nm) with κ slightly above 0.2, a highly hygroscopic mode (150 nm < Dp < 1 μm) with κ greater than 0.3 and a nearly hydrophobic mode (Dp > 1 μm) with κ of about 0.1. The peak of the κ curve appears around 450 nm with a maximum value of 0.35. The derived κ values are consistent with results measured with a high humidity tandem differential mobility analyzer within the size range of 50–250 nm. Inorganics are the predominant species contributing to particle hygroscopicity, especially for particles between 150 nm and 1 μm. For example, NH4NO3, H2SO4, NH4HSO4 and (NH4)2SO4 account for nearly 90% of κ for particles of around 900 nm. For ultrafine particles, WSOC plays a critical role in particle hygroscopicity due to the predominant mass fraction of OM in ultrafine particles. WSOC for particles of around 30 nm contribute 52% of κ. Aerosol hygroscopicity is related to synoptic transport patterns. When southerly wind dominates, particles are more hygroscopic; when northerly wind dominates, particles are less hygroscopic. Aerosol hygroscopicity also has a diurnal variation, which can be explained by the diurnal evolution of planetary boundary layer, photochemical aging processes during daytime and enhanced black carbon emission at night. κ is highly correlated with mass fractions of SO42−, NO3− and NH4+ for all sampled particles as well as with the mass fraction of WSOC for particles of less than 100 nm. A parameterization scheme for κ is developed using mass fractions of SO42−, NO3−, NH4+ and WSOC due to their high correlations with κ, and κ calculated from the parameterization agrees well with κ derived from the particle's chemical composition. Further analysis shows that the parameterization scheme is applicable to other aerosol studies in China.

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Effects of Strategic Tillage on Soil Physicochemical Properties and Grain Yield in the North China Plain

Agronomy ◽

10.3390/agronomy10081167 ◽

2020 ◽

Vol 10 (8) ◽

pp. 1167

Author(s):

Qiuyue Liu ◽

Zhengrong Kan ◽

Cong He ◽

Hailin Zhang

Keyword(s):

Physicochemical Properties ◽

Soil Compaction ◽

Crop Production ◽

North China Plain ◽

North China ◽

Soil Depth ◽

Soil Physicochemical Properties ◽

The North ◽

The North China Plain ◽

No Till

No-till (NT) practice has been widely adopted to improve soil quality, but soil compaction and soil organic carbon (SOC) stratification under long-term NT limit crop production. Strategic tillage (ST), based on single tillage, is proposed as an attractive management practice to sustain the benefits of continuous NT and mitigate its adverse effects. Four tillage systems, including continuous rotary tillage (RT), NT, rotary tillage + subsoiling (RS), and no-till + subsoiling (NS), were implemented to investigate the effects of strategic tillage (i.e., RS and NS) on soil physical properties (compaction and aggregates), SOC, and crop yield in the North China Plain (NCP). The results showed that ST as expected decreased soil bulk density, penetration resistance, and SOC stratification compared with RT and NT at 0–20 cm soil depth (p < 0.05). At 0–10 cm soil depth, more macroaggregates (>0.25 mm) were observed in NT and NS, contributing to higher mean weight and geometric mean diameters, this compared with RT and RS. Additionally, macroaggregate associated SOC was higher, thus resulting in higher SOC storage in NT (31.4–33.4 Mg ha −1) and NS (33.3–35.4 Mg ha−1) at 0–30 cm depth (p < 0.05). Low soil compaction and high SOC in NS were beneficial for the grain yield of wheat and maize, significantly higher by 8.7–32.5% and 14.0–29.8% compared with the other treatments, respectively (p < 0.05). Based on our findings, NS seems to be a promising alternative tillage system to improve soil physicochemical properties and crop production in the NCP. More studies are therefore needed to better understand the benefit of NS.

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Recent Ground Subsidence in the North China Plain, China, Revealed by Sentinel-1A Datasets

Remote Sensing ◽

10.3390/rs12213579 ◽

2020 ◽

Vol 12 (21) ◽

pp. 3579

Author(s):

Min Shi ◽

Huili Gong ◽

Mingliang Gao ◽

Beibei Chen ◽

Shunkang Zhang ◽

...

Keyword(s):

Synthetic Aperture Radar ◽

Land Subsidence ◽

North China Plain ◽

North China ◽

Synthetic Aperture ◽

Groundwater Depletion ◽

Integrated Analysis ◽

The North ◽

The North China Plain ◽

Aperture Radar

Groundwater resources have been exploited and utilized on a large scale in the North China Plain (NCP) since the 1970s. As a result of extensive groundwater depletion, the NCP has experienced significant land subsidence, which threatens geological stability and infrastructure health and exacerbates the risks of other geohazards. In this study, we employed multi-track Synthetic Aperture Radar (SAR) datasets acquired by the Sentinel-1A (S1A) satellite to detect spatial and temporal distributions of surface deformation in the NCP from 2016 to 2018 based on multi-temporal interferometric synthetic aperture radar (MT-InSAR). The results show that the overall ground displacement ranged from −165.4 mm/yr (subsidence) to 9.9 mm/yr (uplift) with a standard variance of 28.8 mm/yr. During the InSAR monitoring period, the temporal pattern of land subsidence was dominated by a decreasing tendency and the spatial pattern of land subsidence in the coastal plain exhibited an expansion trend. Validation results show that the S1A datasets agree well with levelling data, indicating the reliability of the InSAR results. With groundwater level data, we found that the distribution of subsidence in the NCP is spatially consistent with that of deep groundwater depression cones. A comparison with land use data shows that the agricultural usage of groundwater is the dominant mechanism responsible for land subsidence in the whole study area. Through an integrated analysis of land subsidence distribution characteristics, geological data, and previous research results, we found that other triggering factors, such as active faults, precipitation recharge, urbanization, and oil/gas extraction, have also impacted land subsidence in the NCP to different degrees.

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Measurement report: On the difference of aerosol hygroscopicity between high and low RH conditions in the North China Plain

10.5194/acp-2021-1010 ◽

2022 ◽

Author(s):

Jingnan Shi ◽

Juan Hong ◽

Nan Ma ◽

Qingwei Luo ◽

Yao He ◽

...

Keyword(s):

Chemical Composition ◽

North China Plain ◽

North China ◽

Rural Site ◽

Formation Processes ◽

The North ◽

The North China Plain ◽

Secondary Formation ◽

Primary Emissions ◽

Aerosol Hygroscopicity

Abstract. Atmospheric processes, including both primary emissions and secondary formation, may exert complex effects on aerosol hygroscopicity, which is of significant importance in understanding and quantifying the effect of aerosols on climate and human health. In order to explore the influence of local emissions and secondary formation processes on aerosol hygroscopicity, we investigated the hygroscopic properties of submicron aerosol particles at a rural site in the North China Plain (NCP) in winter 2018. This was conducted by simultaneous measurements of aerosol hygroscopicity and chemical composition, using a self-assembled hygroscopic tandem differential mobility analyzer (HTDMA) and a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM). The hygroscopicity results showed that the particles during the entire campaign were mainly externally mixed, with a more hygroscopic (MH) mode and a less hygroscopic (LH) particles mode. The mean hygroscopicity parameter values (κmean) derived from hygroscopicity measurements for particles at 60, 100, 150, and 200 nm were 0.16, 0.18, 0.16, and 0.15, respectively. During this study, we classified two distinct episodes with different RH/T conditions, indicative of different primary emissions and secondary formation processes. It was observed that aerosols at all measured sizes were more hygroscopic under the high RH (HRH) episode than those under the low RH (LRH) episode. During the LRH, κ decreased with increasing particle size, which may be explained by the enhanced domestic heating at low temperature, causing large emissions of non- or less-hygroscopic primary aerosols. This is particularly obvious for 200 nm particles, with a dominant number fraction (> 50 %) of LH mode particles. Using O : C-dependent hygroscopic parameters of secondary organic compounds (κSOA), closure analysis between the HTDMA_measured κ and the ACSM_derived κ was carried out. The results showed that κSOA under the LRH episode was less sensitive to the changes in organic oxidation level, while κSOA under the HRH had a relatively stronger dependency on the organic O : C. This feature suggests that the different sources and aerosol evolution processes, partly resulting from the variation in atmospheric RH/T conditions, may lead to significant changes in aerosol chemical composition, which will further influence their corresponding physical properties.

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Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-20885-2013 ◽

2013 ◽

Vol 13 (8) ◽

pp. 20885-20922 ◽

Cited By ~ 5

Author(s):

H. J. Liu ◽

C. S. Zhao ◽

B. Nekat ◽

N. Ma ◽

A. Wiedensohler ◽

...

Keyword(s):

Chemical Composition ◽

Ultrafine Particles ◽

Mass Fraction ◽

North China Plain ◽

North China ◽

Aerosol Particles ◽

The North ◽

The North China Plain ◽

Mass Fractions ◽

Particulate Mass

Abstract. Hygroscopic growth of aerosol particles is of significant importance in quantifying the aerosol radiative effect in the atmosphere. In this study, hygroscopic properties of ambient particles are investigated based on particle chemical composition at a suburban site in the North China Plain during the HaChi campaign (Haze in China) in summer 2009. The size-segregated aerosol particulate mass concentration as well as the particle components such as inorganic ions, organic carbon and water-soluble organic carbon (WSOC) is identified from aerosol particle samples collected with a 10-stage impactor. An iterative algorithm is developed to evaluate the hygroscopicity parameter κ from the measured particle chemical compositions. During the HaChi summer campaign, almost half of the mass concentration of particles between 150 nm and 1 μm is contributed by inorganic species. Organic matter (OM) is abundant in ultrafine particles, and 77% of the particulate mass with diameter (Dp) around 30 nm is composed of OM. A large fraction of coarse particle mass is undetermined and is assumed to be insoluble mineral dust and liquid water. The campaign average size distribution of κ values shows three distinct modes: the less hygroscopic mode (Dp < 150 nm) with κ slightly above 0.2, the highly hygroscopic mode (150 nm 1 μm) with κ about 0.1. The peak of the κ curve appears around 450 nm with a maximum value of 0.35. The derived κ values are consistent with results measured with a High Humidity Tandem Differential Mobility Analyzer within the size range of 50 nm to 250 nm. Inorganics are the predominant species contributing to particle hygroscopicity, especially for particles between 150 nm and 1 μm. For example, NH4NO3, H2SO4, NH4HSO4 and (NH4)2SO4 account for nearly 90% of κ for particles around 900 nm. For ultrafine particles, WSOC plays a critical role in particle hygroscopicity due to the predominant mass fraction of OM in ultrafine particles. 52% of κ is contributed by WSOC for particles around 30 nm. Aerosol particles are more hygroscopic during daytime, which can result from the diurnal evolution of planetary boundary layer, photochemical aging process during daytime and enhanced elemental carbon emission at night. κ is highly correlated with mass fractions of SO42−, NO3− and NH4+ for all sampled particles as well as with the mass fraction of WSOC for particles less than 100 nm. A parameterization scheme of κ is developed using mass fractions of SO42−, NO3−, NH4+ and WSOC due to their high correlations with κ, and κ calculated from parameterization agrees well with κ derived from the particle chemical composition. Further analysis shows that the parameterization scheme is applicable to other aerosol studies in China.

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Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN): integrated analysis and intensive winter campaign 2018

10.5194/egusphere-egu21-8388 ◽

2021 ◽

Author(s):

Guo Li ◽

Hang Su ◽

Uwe Kuhn ◽

Guangjie Zheng ◽

Ulrich Pöschl ◽

...

Keyword(s):

North China Plain ◽

North China ◽

Chem Phys ◽

High Humidity ◽

The North ◽

The North China Plain ◽

Low Humidity ◽

Haze Formation ◽

Chemistry Experiment

In the recent decade, frequently occurring severe haze events in the North China Plain (NCP) have triggered numerous studies on the underlying formation mechanisms, and the contribution of multiphase chemistry on haze formation becomes one of the focal points. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes in aerosols and fogs. We integrated observations on multiple platforms with regional and box model simulations to identify and characterize the key oxidation processes producing sulfate, nitrate and secondary organic aerosols. An outdoor twin-chamber system was deployed to conduct kinetic experiments under real atmospheric conditions in comparison to literature kinetic data from laboratory studies. The experiments were spanning multiple years since 2017 and an intensive field campaign was performed in the winter of 2018. The location of the site minimizes fast transition between clean and polluted air masses, and regimes representative for the North China Plain were observed at the measurement location in Gucheng near Beijing. The consecutive multi-year experiments document recent trends of PM2.5 pollution and corresponding changes of aerosol physical and chemical properties, enabling in-depth investigations of established and newly proposed chemical mechanisms of haze formation. This study is mainly focusing on the data obtained from the winter campaign 2018. To investigate multiphase chemistry, the results are presented and discussed by means of three characteristic cases: low humidity, high humidity and fog. We find a strong relative humidity dependence of aerosol chemical compositions, suggesting an important role of multiphase chemistry. Compared with the low humidity period, both PM1 and PM2.5 show higher mass fraction of secondary inorganic aerosols (SIA, mainly as nitrate, sulfate and ammonium) and secondary organic aerosols (SOA) during high humidity and fog episodes. The changes in aerosol composition further influence aerosol physical properties, e.g., with higher aerosol hygroscopicity parameter k and single scattering albedo SSA under high humidity and fog cases. The campaign-averaged aerosol pH is 5.1 &#177; 0.9, of which the variation is mainly driven by the aerosol water content (AWC) concentrations. Overall, the McFAN experiment provides new evidence of the key role of multiphase reactions in regulating aerosol chemical composition and physical properties in polluted regions.References:<ul><li>Y. Cheng, et al., Sci. Adv., 2016, 2, e1601530.</li> <li>G. J. Zheng, et al., Atmos. Chem. Phys., 2015, 15, 2969-2983.</li> <li>W. Tao, et al., Atmos. Chem. Phys., 2020, 20, 11729-11746.</li> <li>H. Su, et al., Acc. Chem. Res., 53, 2034-2043.</li> <li>G. Zheng, et al., Science, 2020, 369, 1374-377.</li> <li>G. Li, et al., Faraday Discussions, 2021, DOI: 10.1039/D0FD00099J.</li> </ul>

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Bimodal distribution of size-resolved particle effective density in a rural environment in the North China Plain

10.5194/acp-2021-463 ◽

2021 ◽

Author(s):

Yaqing Zhou ◽

Nan Ma ◽

Qiaoqiao Wang ◽

Zhibin Wang ◽

Chunrong Chen ◽

...

Keyword(s):

Chemical Composition ◽

North China Plain ◽

North China ◽

Geometric Mean ◽

Bimodal Distribution ◽

Effective Density ◽

The North ◽

The North China Plain ◽

Early Afternoon ◽

The Impact

Abstract. Effective density is one of the most important physical properties of atmospheric particles. It is closely linked to particle chemical composition and morphology, and could provide special information on particle emissions and aging processes. In this study, size-resolved particle effective density was measured with a combined DMA-CPMA-CPC system in Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) in autumn 2019. With a new developed flexible Gaussian fit algorithm, frequent (77–87 %) bimodal distribution of particle effective density is identified, with a low-density mode (named sub-density mode) accounting for 22–27 % of total observed particles. The prevalence of the sub-density mode is closely related to fresh black carbon (BC) emissions. The geometric mean for the main-density mode (eff,main) increases from 1.18 g cm−3 (50 nm) to 1.37 g cm−3 (300 nm) due to larger fraction of high-density components and more significant restructuring effect at large particle sizes, but decreases from 0.89 g cm−3 (50 nm) to 0.62 g cm−3 (300 nm) for the sub-density mode (eff,sub) ascribed to the agglomerate effect. eff,main and eff,sub show similar diurnal cycles with peaks in the early afternoon, mainly attributed to the increasing mass fraction of high material density components associated with secondary aerosol production, especially of secondary inorganic aerosol (SIA). To investigate the impact of chemical composition, bulk particle effective density was calculated based on measured chemical composition (ρeff,ACSM) and compared with the average effective density at 300 nm (eff,tot,300 nm). The best agreement between the two densities is achieved when assuming a BC effective density of 0.60 g cm−3. The particle effective density is highly dependent on SIA and BC mass fractions. The influence of BC on the effective density is even stronger than SIA, implying the importance and necessity of including BC in the estimate of effective density for ambient particles.

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