Abstract
Severe events of wintertime particulate air pollution in Beijing (winter haze) are associated with high relative humidity (RH) and fast production of particulate sulfate from the oxidation ...of sulfur dioxide (SO
2
) emitted by coal combustion. There has been considerable debate regarding the mechanism for SO
2
oxidation. Here we show evidence from field observations of a haze event that rapid oxidation of SO
2
by nitrogen dioxide (NO
2
) and nitrous acid (HONO) takes place, the latter producing nitrous oxide (N
2
O). Sulfate shifts to larger particle sizes during the event, indicative of fog/cloud processing. Fog and cloud readily form under winter haze conditions, leading to high liquid water contents with high pH (>5.5) from elevated ammonia. Such conditions enable fast aqueous-phase oxidation of SO
2
by NO
2
, producing HONO which can in turn oxidize SO
2
to yield N
2
O.This mechanism could provide an explanation for sulfate formation under some winter haze conditions.
Secondary organic aerosol (SOA) produced by atmospheric oxidation of primary emitted precursors is a major contributor to fine particulate matter (PM
) air pollution worldwide. Observations during ...winter haze pollution episodes in urban China show that most of this SOA originates from fossil-fuel combustion but the chemical mechanisms involved are unclear. Here we report field observations in a Beijing winter haze event that reveal fast aqueous-phase conversion of fossil-fuel primary organic aerosol (POA) to SOA at high relative humidity. Analyses of aerosol mass spectra and elemental ratios indicate that ring-breaking oxidation of POA aromatic species, leading to functionalization as carbonyls and carboxylic acids, may serve as the dominant mechanism for this SOA formation. A POA origin for SOA could explain why SOA has been decreasing over the 2013-2018 period in response to POA emission controls even as emissions of volatile organic compounds (VOCs) have remained flat.
China experiences severe particulate pollution, especially in winter, and determining the characteristics of particulate matter (PM) during pollution events is imperative for understanding the ...sources and causes of the pollution. However, inconsistencies have been found in the aerosol composition, sources and secondary processing among reported studies. Modern meta-analysis was used to probe the PM chemical characteristics and processing in winter at four representative regions of China, and the first finding was that secondary aerosol formation was the major effect factor for PM pollution. The secondary inorganic species behaved differently in the four regions: sulfate, nitrate, and ammonium increased in the Beijing–Tianjin–Hebei (BTH) and Guanzhong (GZ) areas, but only nitrate increased in the Pearl River Delta (PRD) and Yangtze River Delta (YRD) regions. The increased production of secondary organic aerosol (SOA) was probably caused by aqueous-phase processing in the GZ and BTH regions and by photochemical reactions in the PRD. Finally, we suggest future AMS/ACSM observations should focus on the aerosol characteristics in rural areas in winter in China.
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•A Meta-analysis was conducted to characterize aerosol pollution in winter in China•Particulate pollution are driven by secondary formation•The SOA formation was attributed to aqueous processing in northern China•The SOA formation was attributed to photochemical reactions in the PRD region
Owing to the complex nature and dynamic behaviors of secondary organic aerosol (SOA), its ability to cause oxidative stress (known as oxidative potential, or OP) and adverse health outcomes remains ...poorly understood. In this work, we probed the linkages between the chemical composition of SOA and its OP, and investigated impacts from various SOA evolution pathways, including atmospheric oligomerization, heterogeneous oxidation, and mixing with metal. SOA formed from photooxidation of the two most common polycyclic aromatic hydrocarbons (naphthalene and phenanthrene) were studied as model systems. OP was evaluated using the dithiothreitol (DTT) assay. The oligomer-rich fraction separated by liquid chromatography dominates DTT activity in both SOA systems (52 ± 10 % for naphthalene SOA (NSOA), and 56 ± 5 % for phenanthrene SOA (PSOA)). Heterogeneous ozonolysis of NSOA was found to enhance its OP, which is consistent with the trend observed in selected individual oxidation products. DTT activities from redox-active organic compounds and metals were found to be not additive. When mixing with highly redox-active metal (Cu), OP of the mixture decreased significantly for 1,2-naphthoquinone (42 ± 7 %), 2,3-dihydroxynaphthalene (35 ± 1 %), NSOA (50 ± 6 %), and PSOA (43 ± 4 %). Evidence from proton nuclear magnetic resonance (1H NMR) spectroscopy illustrates that such OP reduction upon mixing can be ascribed to metal–organic binding interactions. Our results highlight the role of aerosol chemical composition under atmospheric aging processes in determining the OP of SOA, which is needed for more accurate and explicit prediction of the toxicological impacts from particulate matter.
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•9,484 PM2.5 organic molecules formed human serum albumin adductome, indicating internal exposure potential.•Internalizable PM2.5 fraction varied 11.9–61.3%, averaging ...26.2%.•Lignin-like and lipid-like WSOM were primarily responsible for the internal exposure potential.
Water-soluble organic molecules (WSOMs) in inhaled PM2.5 can readily translocate from the lungs into the blood circulation, facilitating their distribution to and health effects on distant organs and tissues in the human body. Human serum albumin (HSA), the most abundant protein carrier in the blood, readily binds exogenous substances to form non-covalent adducts and subsequently transports them throughout the circulatory system, thereby indicating their internal exposure. The direct internal exposure of WSOMs in PM2.5 needs to be understood. In this study, the non-covalent HSA-WSOM adductome was developed as a dosimeter to evaluate the internal exposure potential of WSOMs in urban PM2.5. The WSOM composition was acquired from non-target high-resolution mass spectrometry analysis coupled with multiple ionizations. The binding level of HSA-WSOM non-covalent adducts was obtained from surface plasma resonance. Machine learning combined WSOM composition and the binding level of HSA-WSOM non-covalent adducts to screen bindable (also internalizable) WSOMs. The concentration of WSOM ranged from 4 to 13 μg/m3 during our observation period. Of the 17,513 mass spectral features detected, 9,484 contributed to the non-covalent adductome and possessed the internal exposure potential. 102 major contributors accounted for 90.6 % of the HSA-WSOM binding level. The fraction of internalizable WSOMs in PM2.5 varied from 11.9 % to 61.3 %, averaging 26.2 %. WSOMs that have internal exposure potential were primarily lignin-like and lipid-like substances. The HSA-WSOMs non-covalent adductome represents direct internal exposure potential, which can provide crucial insights into the molecular diagnosis of PM2.5 exposure and precise assessments of PM2.5 health effects.
Non‐methane volatile organic compounds (NMVOCs) have a significant impact on air quality in urban areas. Detecting NMVOCs emission with its proxy HCHO on urban scales from space, however, has been ...limited by the lack of discernible enhancement. Here we show clear urban HCHO plumes from 16 cities over the globe by rotating TROPOspheric Monitoring Instrument HCHO pixels according to wind directions. We fit the downwind structure of the plumes with the exponentially modified Gaussian approach to quantify urban HCHO effective production rates between 7.0 and 88.5 mol s−1. Our results are in line with total NMVOC emissions from the EDGAR inventory (r = 0.76). Our work offers a new measure of total NMVOC emissions from urban areas and highlights the potential of satellite HCHO data to provide new information for monitoring urban air quality.
Plain Language Summary
Non‐methane volatile organic compounds (NMVOCs) play an important role in urban air quality. Formaldehyde (HCHO) satellite observations have been shown to be able to reliably track and quantify NMVOC emissions at global and regional scales. Here, we use state‐of‐the‐art satellite sensors to quantify effective HCHO production rates in 16 global cities and further constrain total NMVOC emissions. Our results are broadly consistent with current emissions inventories, implying that satellites may be able to provide new information for urban air studies.
Key Points
We show clear urban HCHO plumes from 16 cities over the globe by relating satellite pixels with wind fields
We obtain urban effective HCHO production rates by fitting the downwind structure of HCHO plumes
Satellite‐based effective HCHO production rates provide potential measures of total non‐methane volatile organic compound emissions
Brown carbon (BrC) absorption impacts radiative forcing and climate change. Quantifying radiative forcing of BrC requires understanding its molecular composition and absorption characteristics. While ...organic molecules surrounding BrC may impact its absorption, their effects have not yet been investigated. This research determined matrix effect on BrC absorption by comparing individual BrC molecules and BrC within an organic matrix. Over 20,000 water‐soluble organic molecules constituted the water‐soluble BrC and associated organic matrix. The matrix enhanced aliphatic BrC absorption but suppressed aromatic BrC, especially with higher matrix O/C ratios indicating greater polarity and acidity. By directly measuring and modeling organic matrix effect on BrC, we can improve climate prediction precision and aerosol‐radiation interaction comprehension.
Plain Language Summary
In the atmosphere, organic carbon that absorb light are called brown carbon. Brown carbon can impact climate change. It is critical to understand potential factors affecting brown carbon's absorption of light. Our study proposed another potential influencing light absorbing of brown carbon, effect from organic matrix formed by co‐existing organic molecules. The matrix effect on brown carbon absorption was simulated by the absorption properties of individual molecules and the absorption contributions from the same molecules embedded within organic matrix. We found over 20,000 molecules in all samples, separating them into major contributing brown carbon molecules and co‐existing organic molecules. We found CHO and CHON formed the majority of these molecules. The organic matrix showed the different behavior to effect light absorption to different portion for organic molecules, namely aliphatic and aromatic brown carbon molecules. The brown carbon absorption was suppressed during the nighttime, with the high O/C ratio co‐existing organics. Through the direct measurement and modeling of organic matrix effect on brown carbon, the finding could improve the precision of climate predictions and enhance our comprehension of aerosol‐radiation interactions.
Key Points
Organic molecules co‐existing around brown carbon constituted the organic matrix
The organic matrix enhanced aliphatic but suppressed aromatic brown carbon absorption
Higher matrix O/C ratios indicating greater polarity and acidity especially suppressed aromatic brown carbon absorption
Abstract The recovery of the ozone layer relies on decreasing atmospheric mixing ratios of ozone-depleting substances (ODSs), including chlorofluorocarbons (CFCs). A significant decline in the mixing ...ratio of trichlorofluoromethane (CFC-11 or CCl 3 F ), the second most abundant CFC, has been observed since the mid-1990s. However, a slowdown in the decline after 2012 indicates a rise in emissions, particularly in Eastern Asia. Ground-based observations are lacking in southeastern China, limiting a thorough evaluation of CFC-11 levels and emissions in this region. A new Advanced Global Atmospheric Gases Experiment background station was established at Xichong (XCG), Shenzhen, China, to provide high-frequency continuous in situ observations. The annual mean CFC-11 mixing ratio, recorded from May 2022 to April 2023, is 221.64 ± 2.29 ppt. When compared with a monthly (MHD) or daily (MLO) observation, this value is found to be 0.45% to 5.36% higher than the northern hemispheric background. With the inverse modeling and interspecies correlation method, we estimate CFC-11 emissions in southeastern China between 1.23 ± 0.25 Gg yr −1 and 1.58 ± 0.21 Gg yr −1 , in line with the bottom-up estimation of 1.50 Gg yr −1 . Results indicate that CFC-11 emissions in the Pearl River Delta region have returned to levels before 2010, aligning with regional and global trends. Observations from XCG would compensate for the deficiency of CFC-11 measurements in southeastern China, paving the road for ODS studies in this region and beyond.
The contributions of chemical composition and emission sources to aerosol optical properties were evaluated for a coastal city in southern China. The average dry light scattering coefficient ...(bscat,dry) and light absorption coefficient (babs) were 32.5 ± 15.5 Mm−1 and 8.8 ± 4.7 Mm−1, respectively. Diurnal cycles in bscat,dry and babs were observed with peak values in the morning and at night. Both bscat,dry and babs varied with wind speeds and directions, and thus affected by transport pathways. Chemical composition data for 12-h PM2.5 samples were used with the revised IMPROVE algorithm and a Hybrid Environmental Receptor Model to evaluate aerosol composition and source contributions to dry light extinction (bext,dry = bscat,dry + babs), respectively. Ammonium sulfate and organic matter were the dominant contributors to bext,dry, followed by elemental carbon, sea salt, fine soil, and ammonium nitrate. The six PM2.5 sources identified were secondary sulfate source, biomass burning, marine emission, fugitive dust, traffic-related emission, and shipping emission. Marine emission and secondary sulfate source were the largest contributors of bext,dry during the daytime and nighttime, respectively. Backward trajectory analysis further explored the impact of potential sources to bext,dry at Sanya from surrounding regions. The results of our study would be useful for improving models of radiative effects from different sources in this area.
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•The lower bscat,dry and babs were consistent with better air quality at Sanya.•Ammonium sulfate and organic matter contributed most to bext,dry.•Source contributions to bext,dry changed from the daytime to the nighttime.•Much higher contribution of biomass burning to bext,dry was found from Southeast Asia.
In the photochemical denitrogenation of 1,4‐diaryl‐2,3‐diazabicyclo2.2.1heptane (AZ6) bearing sterically hindered substituents, a curious new absorption band at about 450 nm was observed under ...low‐temperature matrix conditions, together with the previously well‐characterized planar singlet diradical pl‐1DR6 with λmax=≈580 nm. The 450 nm species was electron paramagnetic resonance (EPR)‐silent. Instead of generating the planar diradical pl‐1DR6 and the precursor azoalkane AZ6 upon warming, the ring‐closed bicyclo2.1.0pentane derivative SB6, that is, the AZ6 denitrogenation product was identified. Based on product analysis, low‐temperature spectroscopic observations, high‐level quantum‐mechanical computations, viscosity effect, and laser‐flash photolysis, the puckered singlet diradicaloid puc‐1DR6 was assigned to the new 450 nm absorption. The latter was detected experimentally at the same time as the planar singlet diradical pl‐1DR6. Sterically demanding substituents as well as viscosity impediments were essential for the detection of the experimentally hitherto unknown puckered singlet cyclopentane‐1,3‐diyl diradicaloid puc‐1DR6, that is, the third isomer in homolysis. The present findings should stimulate future work on the mechanistically fascinating stereoselectivity documented in the formation of bicyclo2.1.0pentanes during the 2,3‐diazabicyclo2.2.1heptane denitrogenation.
Translation
Frozen intermediate: The experimentally hitherto unknown puckered singlet cyclopentane‐1,3‐diyl diradicaloid, that is, the third isomer in azoalkane denitrogenation has been observed experimentally for the first time (see figure). Careful selection of appropriate bulky substituents and low‐temperature reaction conditions enabled the direct spectral observation of this elusive intermediate.
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