ORCID Profile
0000-0001-7084-3861
Current Organisation
University of Basel
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Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.ENVPOL.2017.09.016
Abstract: During the 2016 Hangzhou G20 Summit, the chemical composition of submicron particles (PM
Publisher: American Chemical Society (ACS)
Date: 07-10-2023
Publisher: Elsevier BV
Date: 06-2021
Publisher: Copernicus GmbH
Date: 30-09-2022
Publisher: American Geophysical Union (AGU)
Date: 03-07-2021
DOI: 10.1029/2021GL093465
Abstract: We investigated the photosensitizing properties of secondary organic aerosol (SOA) formed during the hydroxyl radical (OH) initiated oxidation of naphthalene. This SOA was injected into an aerosol flow tube and exposed to UV radiation and gaseous volatile organic compounds or sulfur dioxide (SO 2 ). The aerosol particles were observed to grow in size by photosensitized uptake of d‐limonene and β‐pinene. In the presence of SO 2 , a photosensitized production (0.2–0.3 µg m −3 h −1 ) of sulfate was observed at all relative humidity (RH) levels. Some sulfate also formed on particles in the dark, probably due to the presence of organic peroxides. The dark and photochemical pathways exhibited different trends with RH, unraveling different contributions from bulk and surface chemistry. As naphthalene and other polycyclic aromatics are important SOA precursors in the urban and suburban areas, these dark and photosensitized reactions are likely to play an important role in sulfate and SOA formation.
Publisher: Elsevier BV
Date: 09-2021
Publisher: American Geophysical Union (AGU)
Date: 16-09-2022
DOI: 10.1029/2022GL098035
Abstract: 28 snowpack s les were collected across northern Xinjiang, northwestern China in January 2018. 16 of these liquid snowmelt s les, 15 with pH 6.8 and one with the highest nitrate anion (NO 3 − ) concentration, were selected to investigate the photochemical gaseous nitrous acid (HONO) production rate (P(HONO) (g) ), which was observed to range from 4.0 to 180.9 ppt min −1 at room temperature. Surprisingly, the ratio of HONO production rate and NO 3 − concentration (P(HONO) (g) /[NO 3 ˉ]) was significantly higher than those obtained from the photolysis of aqueous NO 3 − solutions with similar pH, due to the complex organic compounds present in the snowmelt s les, enhancing HONO formation or the coexistence of other photochemical HONO sources. We also found that P(HONO) (g) was highly correlated with the pH of snowmelt s les, which were significantly lower in rural/remote areas than those from urban/industrial sites, suggesting a significant influence of anthropogenic activities on pH and P(HONO) (g) of snowmelt.
Publisher: Copernicus GmbH
Date: 27-02-2023
Abstract: Abstract. In this study, we developed an approach that integrated multiple patterns of timescale for box modeling (MCMv3.3.1) to better understand the O3–precursor relationship at multiple sites and through continuous observations. A 5-month field c aign was conducted in the summer of 2019 to investigate the ozone formation chemistry at three sites in a major prefecture-level city (Zibo) in Shandong Province of northern China. It was found that the relative incremental reactivity (RIR) of major precursor groups (e.g., anthropogenic volatile organic compounds (AVOCs), NOx) was overall consistent in terms of timescales changed from wider to narrower (four patterns: 5-month, monthly, weekly, and daily) at each site, though the magnitudes of RIR varied at different sites. The time series of the photochemical regime (using RIRNOx / RIRAVOC as an indicator) in weekly or daily patterns further showed a synchronous temporal trend among the three sites, while the magnitude of RIRNOx / RIRAVOC was site-to-site dependent. The derived RIR ranking (top 10) of in idual AVOC species showed consistency between three patterns (i.e., 5-month, monthly, and weekly). It was further found that the c aign-averaging photochemical regimes showed overall consistency in the sign but non-negligible variability among the four patterns of timescale, which was mainly due to the embedded uncertainty in the model input dataset when averaging in idual daily patterns into different timescales. This implies that utilizing narrower timescales (i.e., daily pattern) is useful for deriving reliable and robust O3–precursor relationships. Our results highlight the importance of quantifying the impact of different timescales to constrain the photochemical regime, which can formulate more accurate policy-relevant guidance for O3 pollution control.
Publisher: Elsevier BV
Date: 09-2020
Publisher: Springer Science and Business Media LLC
Date: 09-02-2022
DOI: 10.1038/S41612-022-00233-X
Abstract: Secondary organic aerosol (SOA) represents a major fraction of atmospheric fine particles. Both biogenic and anthropogenic volatile organic compounds (VOCs) can contribute to SOA through (photo-) oxidation. However, the current understanding of their combined, interactive effect on SOA formation and composition is still limited, challenging the accuracy in assessing global SOA budget, sources, and climate effect. Here we combine laboratory experiments and modelling to show that isoprene can suppress SOA formation from photo-oxidation of anthropogenic aromatics (toluene and p -xylene) with the presence of NO x , and similar SOA suppression phenomena are observed when replacing isoprene with propene. We find that the decreased SOA in such mixed-VOC conditions can be largely attributed to OH scavenging effect, resulting in reduced consumption of parent aromatics. However, various changes in SOA oxidation state (i.e., O/C) and oxidation pathways (i.e., more carbonyls formation) are observed following addition of isoprene, and the SOA chemical composition may not be similar to any single parent hydrocarbon, which implies the existence of complex interactions between the degradation chemistry for alkenes and aromatics. Under the conditions of this work, the OH scavenging effect is largely determined by gas-phase chemistry, which is expected to be widespread in binary or more complex systems in ambient air. More broadly, we infer that the global budget of anthropogenic SOA and its corresponding radiative forcing could be affected by biogenic emission of isoprene, particularly in urban environments with appreciable vegetation coverage.
Publisher: MDPI AG
Date: 08-05-2022
Abstract: Although carbonyl compounds are a key species with atmospheric oxidation capacity, their concentrations and sources have not been sufficiently characterized in various atmospheres, especially in desert areas. In this study, atmospheric carbonyl compounds were measured from 16 May to 15 June 2018 in Tazhong in the central Taklimakan Desert, Xinjiang Uygur Autonomous Region, China. Concentrations, chemical compositions, and sources of carbonyl compounds were investigated and compared with those of different environments worldwide. The average concentration of total carbonyls during the s ling period was 11.79 ± 4.03 ppbv. Formaldehyde, acetaldehyde, and acetone were the most abundant carbonyls, with average concentrations of 6.08 ± 2.37, 1.68 ± 0.78, and 2.52 ± 0.68 ppbv, respectively. Strong correlations between formaldehyde and other carbonyls were found, indicating same or similar sources and sinks. A hybrid single-particle Lagrangian integrated trajectory was used to analyze 72 h back trajectories. The values of C1/C2 (formaldehyde to acetaldehyde, 3.22–4.59) and C2/C3 (acetaldehyde to propionaldehyde, 15.00–17.03) from different directions and distances of the trajectories were consistent with the characteristics of a remote area. Relative to various environments, the carbonyl concentration in the Tazhong desert site was lower than that in urban areas and higher than that in suburban and remote areas, implying contributions from local primary and secondary sources. The obtained data can be used to improve the source and sink estimation of carbonyls at the regional scale.
Publisher: CSIRO Publishing
Date: 2018
DOI: 10.1071/EN18005
Abstract: Environmental contextChemical mechanisms are an important component of predictive air quality models that are developed using smog chambers. In smog chamber experiments, UV l s are often used to simulate sunlight, and the choice of l can influence the obtained data, leading to differences in model predictions. We investigate the effect of various UV l s on the prediction accuracy of a key mechanism in atmospheric chemistry. AbstractA new smog chamber was constructed at CSIRO following the decommissioning of the previous facility. The new chamber has updated instrumentation, is 35 % larger, and has been designed for chemical mechanism and aerosol formation studies. To validate its performance, characterisation experiments were conducted to determine wall loss and radical formation under irradiation by UV l s. Two different types of blacklights commonly used in indoor chambers are used as light sources, and the results using these different l s are investigated. Gas-phase results were compared against predictions from the latest version of the SAPRC chemical mechanism. The SAPRC mechanism gave accurate results for hydrocarbon reaction and oxidation formation for propene and o-xylene experiments, regardless of the light source used, with variations in ozone concentrations between experiment and modelled results typically less than 10 % over 6-h irradiation. The SAPRC predictions for p-xylene photooxidation showed overprediction in the rate of oxidation, although no major variations were determined in mechanism results for different blacklight sources. Additionally, no significant differences in the yields of aerosol arising from new particle formation were discernible regardless of the light source used under these conditions.
Publisher: Elsevier BV
Date: 04-2020
Publisher: MDPI AG
Date: 05-12-2019
Abstract: A field s ling c aign of volatile organic compounds (VOCs) was conducted during ozone polluted days at three sites of botanic gardens (HP), industrial areas (XS), and traffic residential mixed areas (ZH) in Hangzhou. The s ling was performed using stainless steel canisters from 6:00 to 20:00 synchronously with a time interval of 2 h on 17 May, 26 June, 20 July, 24 August, and 26 September 2018. A total of 107 species of VOCs for each s le were quantified using two standard gases with a pre-concentrator coupled by GC/MS. The Positive Matrix Factorization (PMF) model was used to identify the major VOC sources and assess their contribution to VOC concentrations. The effects of VOCs on O3 formation were investigated, based on propylene-equivalent concentrations (Prop-E), ozone formation potential (OFP), and Smog Production Model (SPM). It was found that the concentration of ozone during the s ling days tended to be highest in the downwind area while the concentrations of VOCs and NO2 in HP were rather low. The most reactive species were isoprene, ethylene, m-xylene, toluene, and propylene. The average total VOC volume mixing ratios in HP, XS, and ZH were 32.00, 36.63, and 50.34 ppbv, respectively. Bimodal profiles of propane and n-butane were exhibited in ZH while unimodal diurnal variation of isoprene was performed in HP. Liquefied petroleum gas/natural gas (LPG/NG) usage, aged background, and secondary source were identified as the major contributors to total VOCs in Hangzhou, accounting for 19.65%, 15.53%, and 18.93%, respectively.
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 04-2018
DOI: 10.1016/J.SCITOTENV.2017.11.180
Abstract: Ammonia (NH
Publisher: Taiwan Association for Aerosol Research
Date: 2017
Publisher: Elsevier BV
Date: 08-2022
DOI: 10.1016/J.CHEMOSPHERE.2022.134608
Abstract: China has implemented two national clean air actions in 2013-2017 and 2018-2020, respectively, with the aim of reducing primary emissions and hence improving air quality at a national level. It is important to examine the effectiveness of such emission reductions and assess the resulting changes in air quality. However, such evaluation is difficult as meteorological factors can lify, or obscure the changes of air pollutants, in addition to the emission reduction. In this study, we applied the random forest machine learning technique to decouple meteorological influences from emissions changes, and examined the deweathered trends of air pollutants in 12 Chinese mega-cities during 2013-2020. The observed concentrations of all criteria pollutants except O
Publisher: Elsevier BV
Date: 02-2017
Publisher: Elsevier BV
Date: 08-2020
Publisher: American Chemical Society (ACS)
Date: 11-02-2022
Abstract: Systemic inflammation is a key mechanism in the development of cardiovascular diseases induced by exposure to fine particles (particles with aerodynamic diameter ≤2.5 μm [PM
Publisher: MDPI AG
Date: 10-01-2020
Abstract: As atmospheric fresh soot particles age, they become coated with other chemical species. This transforms their physicochemical properties and affects their optical characteristics, which is of great importance to air quality, the environment and climate change. One of the predominantly occurring states of soot particles in the ambient environment is the core-shell mixing state. In this study, we used the core-shell model to calculate the optical absorption, scattering and extinction efficiency, absorption proportion and absorption exponent of coated soot particles. We then investigated the effects of different core sizes (D0), incident wavelengths (λ), coating materials and coating thicknesses on these optical characteristics. Absorption efficiency and absorption proportion of soot particles decreased as the coating became thicker, at core sizes of D0 = 20, 50 and 100 nm and λ = 405, 532 and 781 nm, regardless of the type of coating material. As the coating thickness increased, the absorption exponent (β) of inorganic-coated soot particles tended to rise and then fall, while the β value of organic-coated soot particles kept increasing. Our results advance our scientific understanding of the interaction of optical properties with chemical composition, mixing state, and aging processes of soot particles in the atmosphere.
Publisher: Proceedings of the National Academy of Sciences
Date: 03-04-2023
Abstract: Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O 3 and NO 3 radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air–water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces. The measured OH production rates in atmospherically relevant droplets are comparable to or significantly higher than those from known aqueous bulk sources, especially in the dark. As aqueous droplets are ubiquitous in the troposphere, this interfacial source of OH radicals should significantly impact atmospheric multiphase oxidation chemistry, with substantial implications on air quality, climate, and health.
Publisher: Zhejiang University Press
Date: 2018
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.ENVPOL.2019.04.045
Abstract: Haze formation involves many interacting factors, such as secondary aerosol formation, unfavourable synoptic conditions and regional transport. The interaction between these factors complicates scientific understanding of the mechanism behind haze formation. In this study, we investigated the factors resulting in haze events in Longyou, a city located in a basin in China. Aerosol s les of PM
Publisher: American Chemical Society (ACS)
Date: 21-07-2020
Publisher: Copernicus GmbH
Date: 30-09-2022
DOI: 10.5194/ACP-2022-592
Abstract: Abstract. In this study, we developed an approach that integrating multiple patterns of time scale for box modeling (MCMv3.3.1) to better understand the O3-precursor relationship through multiple-site and continuous observations. A five-month field c aign was conducted in the summer of 2019 to investigate the ozone formation chemistry at three sites in a major prefecture-level city (Zibo) in Shandong province of northern China. It was found that the relative incremental reactivity (RIR) of major precursor groups (e.g., anthropogenic volatile organic compound (AVOC), NOx) were overall consistent along with time scale (four patterns: five-month, monthly, weekly, and daily) varied from wider to narrower, though the magnitude of RIR varied at each site. The time series of the photochemical regime (using RIRNOx/RIRAVOC as indicator) in weekly or daily patterns further showed varied magnitude but a synchronous temporal trend among the three sites. The derived RIR ranking (top 10) of in idual AVOC species showed consistency at three averaged patterns (i.e., five-month, monthly, and weekly). It was further found that the c aign-averaging photochemical regimes showed overall consistency but non-negligible variability among the four patterns of time scale, which was mainly due to the embedded uncertainty in model input dataset when averaging in idual daily pattern into different timescales. This implies that integrating multiple patterns of time scale is useful to derive reliable and robust O3-precursor relationship. Our results highlight the importance of quantifying the impact of different time scales to constrain the photochemical regime, which can formulate more accurate policy-relevant guidance for O3 pollution control.
Publisher: Elsevier BV
Date: 11-2017
Publisher: Elsevier BV
Date: 02-2023
Location: No location found
Location: Austria
No related grants have been discovered for Kangwei Li.