| 1. |
- Hallquist, Mattias, 1969, et al.
(författare)
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Photochemical smog in China: scientific challenges and implications for air-quality policies
- 2016
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Ingår i: National Science Review. - : Oxford University Press (OUP). - 2095-5138 .- 2053-714X. ; 3:4, s. 401-403
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Tidskriftsartikel (refereegranskat)abstract
- In large areas of China severe air pollution events pose a significant threat to human health, ecosystems and climate. Current reduction of primary emissions will also affect secondary pollutants such as ozone (O3) and particulate matter (PM), but the magnitude of the effects is uncertain. Major scientific challenges are related to the formation of O3 and secondary particulate matter including Secondary Organic Aerosols (SOA). Large uncertainties also remain regarding the interactions of soot, SOA and O3 under the influence of different SO2, NOX and VOC concentrations. To improve the understanding of these secondary atmospheric interactions in China, scientific areas of central importance for photochemically induced air pollutants have been identified. In addition to the scientific challenges, results from research need to be synthesized across several disciplines and communicated to stakeholders affected by air pollution and to policy makers responsible for developing abatement strategies. Development of these science-policy interactions can benefit from experience gained under the UN ECE Convention on Long Range Transboundary Air Pollution (LRTAP)
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| 2. |
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| 3. |
- Le Breton, Michael, 1986, et al.
(författare)
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Chlorine oxidation of VOCs at a semi-rural site in Beijing: significant chlorine liberation from ClNO2 and subsequent gas- and particle-phase Cl-VOC production
- 2018
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:17, s. 13013-13030:18, s. 13013-13030
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Tidskriftsartikel (refereegranskat)abstract
- Nitryl chloride (ClNO2) accumulation at night acts as a significant reservoir for active chlorine and impacts the following day's photochemistry when the chlorine atom is liberated at sunrise. Here, we report simultaneous measurements of N2O5 and a suite of inorganic halogens including ClNO2 and reactions of chloride with volatile organic compounds (Cl-VOCs) in the gas and particle phases utilising the Filter Inlet for Gas and AEROsols time-of-flight chemical ionisation mass spectrometer (FIGAERO-ToF-CIMS) during an intensive measurement campaign 40 km northwest of Beijing in May and June 2016. A maximum mixing ratio of 2900 ppt of ClNO2 was observed with a mean campaign nighttime mixing ratio of 487 ppt, appearing to have an anthropogenic source supported by correlation with SO2, CO and benzene, which often persisted at high levels after sunrise until midday. This was attributed to such high mixing ratios persisting after numerous e-folding times of the photolytic lifetime enabling the chlorine atom production to reach 2.3 x 10(5) molecules cm(-3) from ClNO2 alone, peaking at 09:30 LT and up to 8.4 x 10(5) molecules cm(-3) when including the supporting inorganic halogen measurements. Cl-VOCs were observed in the particle and gas phases for the first time at high time resolution and illustrate how the iodide ToF-CIMS can detect unique markers of chlorine atom chemistry in ambient air from both biogenic and anthropogenic sources. Their presence and abundance can be explained via time series of their measured and steady-state calculated precursors, enabling the assessment of competing OH and chlorine atom oxidation via measurements of products from both of these mechanisms and their relative contribution to secondary organic aerosol (SOA) formation.
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| 4. |
- Le Breton, Michael, 1986, et al.
(författare)
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Online gas- and particle-phase measurements of organosulfates, organosulfonates and nitrooxy organosulfates in Beijing utilizing a FIGAERO ToF-CIMS
- 2018
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:14, s. 10355-10371
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Tidskriftsartikel (refereegranskat)abstract
- A time-of-flight chemical ionization mass spectrometer (CIMS) utilizing the Filter Inlet for Gas and Aerosol (FIGAERO) was deployed at a regional site 40 km north-west of Beijing and successfully identified and measured 17 sulfur-containing organics (SCOs are organo/nitrooxy organosulfates and sulfonates) with biogenic and anthropogenic precursors. The SCOs were quantified using laboratory-synthesized standards of lactic acid sulfate and nitrophenol organosulfate (NP OS). The variation in field observations was confirmed by comparison to offline measurement techniques (orbitrap and high-performance liquid chromatography, HPLC) using daily averages. The mean total (of the 17 identified by CIMS) SCO particle mass concentration was 210 +/- 110 ng m(-3) and had a maximum of 540 ng m(-3), although it contributed to only 2 +/- 1% of the organic aerosol (OA). The CIMS identified a persistent gas-phase presence of SCOs in the ambient air, which was further supported by separate vapour-pressure measurements of NP OS by a Knudsen Effusion Mass Spectrometer (KEMS). An increase in relative humidity (RH) promoted partitioning of SCO to the particle phase, whereas higher temperatures favoured higher gas-phase concentrations. Biogenic emissions contributed to only 19% of total SCOs measured in this study. Here, C10H16NSO7, a monoterpene-derived SCO, represented the highest fraction (10 %) followed by an isoprene-derived SCO. The anthropogenic SCOs with polycyclic aromatic hydrocarbon (PAH) and aromatic precursors dominated the SCO mass loading (51 %) with C11H11SO7, derived from methyl naphthalene oxidation, contributing to 40 ng m(-3) and 0.3% of the OA mass. Anthropogenic-related SCOs correlated well with benzene, although their abundance depended highly on the photochemical age of the air mass, tracked using the ratio between pinonic acid and its oxidation product, acting as a qualitative photochemical clock. In addition to typical anthropogenic and biogenic precursors the biomass-burning precursor nitrophenol (NP) provided a significant level of NP OS. It must be noted that the contribution analysis here is only representative of the detected SCOs. There are likely to be many more SCOs present which the CIMS has not identified. Gas- and particle-phase measurements of glycolic acid suggest that partitioning towards the particle phase promotes glycolic acid sulfate production, contrary to the current formation mechanism suggested in the literature. Furthermore, the HSO4 center dot H2SO4- cluster measured by the CIMS was utilized as a qualitative marker for acidity and indicates that the production of total SCOs is efficient in highly acidic aerosols with high SO42- and organic content. This dependency becomes more complex when observing individual SCOs due to variability of specific VOC precursors.
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| 5. |
- Liu, Qianyun, et al.
(författare)
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Roadside assessment of a modern city bus fleet: Gaseous and particle emissions
- 2019
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Ingår i: Atmospheric Environment: X. - : Elsevier BV. - 2590-1621. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 The Authors In many cities worldwide, modern fleets have been introduced to reduce gaseous and particle emissions from city buses. To date, most emission studies are limited to a few vehicles, making a statistically significant assessment of control options difficult, especially under real-world driving conditions. Exhaust emissions of 234 individual city buses were measured under real-world stop-and-go traffic conditions at a bus stop in Gothenburg, Sweden. The buses comprised models fulfilling Euro III-VI and EEV (Enhanced Environmentally Friendly Vehicle) standards with different engine technologies, fuels, and exhaust after-treatment systems, and also included hybrid-electric buses (HEV). Both gaseous (NOx, CO, HC, and SO2) and size-resolved particle number (PN) and mass (PM) emission factors (EF) were calculated for vehicles using compressed natural gas (CNG), diesel (DSL), Rapeseed Methyl Ester (RME) and Hydro-treated Vegetable Oil (HVO) equipped with various after-treatment technologies, e.g., diesel particulate filter (DPF), selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) systems. The highest median EFPN was obtained from Euro VHEV-HVO-SCR buses (MdEFPN = 18×1014 # kg-1) when their combustion engines were used though 53% of their accelerations were below detection limits indicating the use of their electrical engine. The highest MdEFPM was obtained from the Euro V-DSL-SCR buses (MdEFPM = 150 mg kg-1) and the lowest from EEV-CNG buses (below detection threshold) and Euro VIHEV-HVO- SCR+EGR+DPF buses (MdEFPM = 19 mg kg-1). The highest MdEFNOx was obtained from the Euro V-RME-SCR (MdEFNOx = 30 g kg-1) and Euro VHEV-HVO-SCR buses (MdEFNOx = 24 g kg-1), and the lowest from CNG buses (MdEFNOx = 4.8 g kg-1) and Euro VIHEV-HVO-SCR+EGR+DPF buses (MdEFNOx = 7.4 g kg-1). Hybrid buses can give higher PN emissions compared to traditional diesel engines, likely due to downsized combustion engines. Replacing diesel by biodiesel fuel reduced MdEFPM significantly but increased MdEFNOx which may be due to the higher combustion temperature and oxygen contents of the fuel (for RME). Overall, the EEV-CNG buses performed the best regarding both the MdEF and low contribution to the high emitters. It was also found that a small (5%) proportion of the buses contributed significantly (14-30%) to the total emissions. Identification and monitoring the maintenance of the high emitters in the fleets should be considered for the improvement of air quality.
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| 6. |
- Boman, Johan, 1955, et al.
(författare)
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PM2.5 at a semi-rural site near Beijing, China
- 2023
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Ingår i: X-Ray Spectrometry. - 0049-8246. ; 52:6, s. 447-56
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Tidskriftsartikel (refereegranskat)abstract
- Breathing clean air is a human right still not accessible to everyone. In most of the world, the air is polluted, which affects both the environment and human health. To investigate the air pollution situation in a semi-rural part of northern China, particles with a diameter below 2.5 & mu;m (PM2.5) were collected in Changping, 40 km northwest of Beijing in May and June 2016. The particles were analyzed for mass, trace elements, and black carbon (BC). The mean PM2.5 mass was 49 & mu;g/m(3), ranging from 3.1 to 266 & mu;g/m(3). S, Cl, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, As, and Pb were determined by Energy Dispersive X-Ray Fluorescence (EDXRF). They constituted 4% of the PM2.5 mass, with BC adding another 3%. Enrichment factor evaluation identified S, Ni, Cu, Zn, As, and Pb as the main anthropogenic contributors to environmental impact. A pollution load index (PLI) of 0.03 showed that the site could not be considered as polluted by the trace elements in PM2.5. Positive matrix factorization (PMF) was used for source apportionment of the PM2.5 content. The PMF analysis reveals that a mixture of mineral dust, fossil fuel combustion, industries, and salts were the main sources of air pollution. The non-carcinogenic and carcinogenic health risks were assessed, and both show a small health risk in the short study period. Following the development of PM2.5 concentrations over time in this part of China shows a decreasing trend of PM2.5 pollution, which is promising for the future.
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| 7. |
- Faxon, Cameron, et al.
(författare)
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Characterization of organic nitrate constituents of secondary organic aerosol (SOA) from nitrate-radical-initiated oxidation of limonene using high-resolution chemical ionization mass spectrometry
- 2018
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18, s. 5467-5481
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Tidskriftsartikel (refereegranskat)abstract
- The gas-phase nitrate radical (NO 3 • ) initiated oxidation of limonene can produce organic nitrate species with varying physical properties. Low-volatility products can contribute to secondary organic aerosol (SOA) formation and organic nitrates may serve as a NO x reservoir, which could be especially important in regions with high biogenic emissions. This work presents the measurement results from flow reactor studies on the reaction of NO 3 • with limonene using a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) combined with a Filter Inlet for Gases and AEROsols (FIGAERO). Major condensed-phase species were compared to those in the Master Chemical Mechanism (MCM) limonene mechanism, and many non-listed species were identified. The volatility properties of the most prevalent organic nitrates in the produced SOA were determined. Analysis of multiple experiments resulted in the identification of several dominant species (including C 10 H 15 NO 6 , C 10 H 17 NO 6 , C 8 H 11 NO 6 , C 10 H 17 NO 7 , and C 9 H 13 NO 7 ) that occurred in the SOA under all conditions considered. Additionally, the formation of dimers was consistently observed and these species resided almost completely in the particle phase. The identities of these species are discussed, and formation mechanisms are proposed. Cluster analysis of the desorption temperatures corresponding to the analyzed particle-phase species yielded at least five distinct groupings based on a combination of molecular weight and desorption profile. Overall, the results indicate that the oxidation of limonene by NO 3 • produces a complex mixture of highly oxygenated monomer and dimer products that contribute to SOA formation.
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| 8. |
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| 9. |
- Pathak, Ravi K., et al.
(författare)
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Influence of Ozone and Radical Chemistry on Limonene Organic Aerosol Production and Thermal Characteristics
- 2012
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Ingår i: Environmental Science & Technology. - : American Chemical Society. - 0013-936X .- 1520-5851. ; 46:21, s. 11660-11669
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Tidskriftsartikel (refereegranskat)abstract
- Limonene has a strong tendency to form secondary organic aerosol (SOA) in the atmosphere and in indoor environments. Initial oxidation occurs mainly via ozone or OH radical chemistry. We studied the effect of O3 concentrations with or without a OH radical scavenger (2-butanol) on the SOA mass and thermal characteristics using the Gothenburg Flow Reactor for Oxidation Studies at Low Temperatures and a volatility tandem differential mobility analyzer. The SOA mass using 15 ppb limonene was strongly dependent on O3 concentrations and the presence of a scavenger. The SOA volatility in the presence of a scavenger decreased with increasing levels of O3, whereas without a scavenger, there was no significant change. A chemical kinetic model was developed to simulate the observations using vapor pressure estimates for compounds that potentially contributed to SOA. The model showed that the product distribution was affected by changes in both OH and ozone concentrations, which partly explained the observed changes in volatility, but was strongly dependent on accurate vapor pressure estimation methods. The model–experiment comparison indicated a need to consider organic peroxides as important SOA constituents. The experimental findings could be explained by secondary condensed-phase ozone chemistry, which competes with OH radicals for the oxidation of primary unsaturated products.
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| 10. |
- Prakash, Jai, et al.
(författare)
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Characterization, sources, and atmospheric transformation of a few key short-lived climate pollutants (SLCPs) at a rural super-site in the Indo-Gangetic Plain (IGP) of India
- 2022
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Ingår i: Environmental Science: Atmospheres. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 2, s. 517-538
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Tidskriftsartikel (refereegranskat)abstract
- The Indo-Gangetic Plain (IGP) region of India faces some of the most severe air pollution problems on Earth that threaten human health, food security, ecosystems, environmental sustainability, and the climate. The aim of this study is to identify and characterize the sources of key short-lived climate pollutants (SLCPs) - black carbon (BC), brown carbon (BrC), and ozone (O3) - as well as other pollutants [carbon monoxide (CO) and nitrogen oxides NOX = NO and NO2], and interlinked atmospheric processes of their formation and transformation at our long-term air pollution monitoring station in a remote rural IGP site, the Indo-Gangetic Plains Centre for Air Research and Education (IGP-CARE). Because of its location, measurements acquired at IGP-CARE provide otherwise new information on the key SLCPs in the IGP region at a remote and rural location. The year-long measurement data at this remote site provided new insights into the variability of SLCP concentration and interlinked atmospheric processes that affect air quality in the rural IGP region. Thirteen episodic events (E1-E13) of elevated BC and BrC concentrations were identified, which can largely be attributed to the local biomass burning activities in the neighboring rural communities. It is suggested that high concentrations of BrC were mostly primary in nature and thought to be co-emitted with BC from biomass burning. Also, secondary pollutant tropospheric O3 showed elevated concentration. O3 peaks were mostly attributed to local ozone formation. Nevertheless, on several occasions, O3 emission was also attributed to regional urban areas. This study's most important finding is that BrC concentrations were relatively high throughout the year with very pronounced diurnal variation with distinct morning and evening peaks in general and a minimum at around noon time; this is hypothesized to be associated with daytime photochemical processes. Analyses using a conditional bivariate probability function (CBPF) and potential source contribution function (PSCF) suggest that regional sources likely affected the local concentrations of SLCPs. These results partly explain the high concentrations and spatial distributions of SLCPs at the local and regional scales at the IGP-CARE site in winter and autumn. In contrast, in the summer and monsoon seasons, strong convection likely favored the dilution of pollutants.
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