Modifications on the coastal atmospheric sulfur and cloud condensation nuclei along the Eastern China seas by shipping fuel transition.

Marine fuel combustion from shipping releases SO2 and forms sulfate particles, which may alter low cloud characteristics. A series of strategies were implemented to control the sulfur content of ship fuel oil from 2018 to 2020, offering insights into the effects of the ship fuel oil transition on sulfur-related pollutants and the consequent cloud condensation nuclei (CCN) in the atmosphere. Compared to 2018 in the southeast China waters, shipping SO2 emission decreased by 78 % in 2020, resulting in a 76 % reduction in ship-related total sulfur concentration, and a decrease of 54 % in CCN number concentration under supersaturation 0.2 % (CCN0.2) contributed by shipping. The response of CCN0.2 to ship-related sulfate modification is more pronounced in relatively clean environments than polluted environments, highlighting the uneven changes in coastal CCN along the Eastern China Sea induced by the ship fuel policies. CCN can trigger the formation of cloud droplets, 2020 fuel regulation may have and will reduce the cooling radiative forcing effect with strong spatial heterogeneity. The study provides insights into the variations in coastal atmospheric sulfur-related pollutants and CCN in uneven response to changes in ship fuel oil, prompting the need for further comprehensive assessments of the climate effects resulting from potential shifts in ship fuel use in the future.

Aging effects on residential biomass burning emissions under quasi-real atmospheric conditions.

Emissions from biomass burning (BB) vastly contribute to the atmospheric trace gases and particles, which affect air quality and human health. After emission, the chemical evolution changes the mass and composition of organic aerosol (OA) in the diluted and aged plume. In this study, we used a quasi-real atmospheric smog chamber system to conduct aging experiments and investigated the multiphase oxidation of primary organic aerosol (POA) and the formation of secondary organic aerosols (SOA) in residential biomass burning plumes. We found that the emissions in the gas and particle phases were interlinked during the plume evolution. During photochemical aging, more oxidized OA was produced, and SOA formation increased by a factor of 2 due to functionalization reactions of gaseous precursors such as furans, phenols, and carbonyls. On the other hand, dark aging resulted in a lower OA mass enhancement by a factor of 1.2, with weaker oxidation from gaseous reactions. Dark aging experiments resulted in the generation of substantial quantities of nitrogen-containing organic compounds in both gas and particulate phases, while photochemical aging led to a notable increase in the concentration of gaseous carboxylic acids. Our observations show that the properties of SOA are influenced by exposure to sunlight radiation and oxidants such as OH or NO3 radicals. These results reflect the aging process of BB plumes in real-world atmospheric conditions and highlight the importance of considering various aging mechanisms.

Source characterization of volatile organic compounds in urban Beijing and its links to secondary organic aerosol formation.

Volatile organic compounds (VOCs) are precursors for ozone and secondary organic aerosol (SOA) formation, thereby playing a vital role in atmospheric chemistry and urban air quality. To characterize the relationship between VOCs and SOA, organics both in gas and particulate phases were concurrently measured in urban Beijing. The VOCs and organic aerosol (OA) were apportioned into factors with different oxidation levels by applying the factorization analysis on their detailed mass spectra. Six factors of VOCs were identified, including four primary VOCs (PVOC) factors and two secondary VOCs (SVOC) factors. The PVOC factors dominated the total VOCs when the air mass originated in the cleaner northern areas, while SVOC factors dominated for polluted southern air masses. The normalized concentrations of PVOC and primary OA factors showed consistent diurnal variations regardless of air mass directions, owing to the relatively stable local emissions during the experimental period. This contrasted with the secondary factors due to more complex transformation processes. The traffic-related VOCs and solid fuel combustion VOCs negatively correlated with SOA, implying that they may have contributed to the SOA formation through photooxidation. The VOCs in lower oxidation levels were found to have poor correlations with the less oxidized SOA, whereas they correlated strongly to the more oxidized SOA. This implied that the less oxidized SOA may be in a transition state, where its production and loss rates were balanced. These served as products of VOCs oxidation and reactants of more oxidized SOA formation, playing important roles on the VOC to SOA transformation. The identified VOC emission sources and their photochemical production of SOA should be considered in air quality policy planning.

[Investigating the Pollutants of Marine Shipping Emissions Along the East China Sea by Combining in-situ Measurements and Automatic Identification System].

Marine shipping emissions have important impacts on air quality and climate. This type of anthropogenic emission remains largely unclear due to complex vessel types and activities. A coastal site near the Ningbo-Zhoushan port along the East China Sea was selected for this study, representing one of the hotspot regions globally with the most intensive shipping activities, in combination with vessels for both domestic and international transportation. Long-term temporal variations in key gaseous and particulate pollutants were obtained at the site using in-situ measurements, and the vessel speed associated with each classified vessel type was obtained according to the automatic identification system (AIS). In combination of backward trajectories, we were able to identify the periods predominated by the surrounding vessel emissions (in warm seasons, dominated by vessels in full operation or idle mode) or influenced by continental outflow (in cold season). We found that emissions of sulphur dioxide (SO2), nitrogen oxides (NOx), and black carbon (BC) aerosol were highly correlated with high-speed vessels, whereas carbon monoxide (CO) was likely related to lower operation speed. The total particulate matter (PM) was not directly linked to vessel activities. The enhancement factor in operation mode compared to that in idle mode was approximately 1-4 for most pollutants. This direct ambient observation of the emissions from a range of mixed vessel types may provide a basis for evaluating the shipping emission inventory.

Connecting the Light Absorption of Atmospheric Organic Aerosols with Oxidation State and Polarity.

The light-absorbing organic aerosol (OA) constitutes an important fraction of absorbing components, counteracting major cooling effect of aerosols to climate. The mechanisms in linking the complex and changeable chemistry of OA with its absorbing properties remain to be elucidated. Here, by using solvent extraction, ambient OA from an urban environment was fractionated according to polarity, which was further nebulized and online characterized with compositions and absorbing properties. Water extracted high-polar compounds with a significantly higher oxygen to carbon ratio (O/C) than methanol extracts. A transition O/C of about 0.6 was found, below and above which the enhancement and reduction of OA absorptivity were observed with increasing O/C, occurring on the less polar and high polar compounds, respectively. In particular, the co-increase of nitrogen and oxygen elements suggests the important role of nitrogen-containing functional groups in enhancing the absorptivity of the less polar compounds (e.g., forming nitrogen-containing aromatics), while further oxidation (O/C > 0.6) on high-polar compounds likely led to fragmentation and bleaching chromophores. The results here may reconcile the previous observations about darkening or whitening chromophores of brown carbon, and the parametrization of O/C has the potential to link the changing chemistry of OA with its polarity and absorbing properties.

Contrasting resistance of polycyclic aromatic hydrocarbons to atmospheric oxidation influenced by burning conditions.

The oxidation of polycyclic aromatic hydrocarbons (PAHs) determines their lifetime, toxicity and consequent environmental and climate impacts. The residential solid fuel burning composes of a substantial fraction of PAH emissions; however, their oxidation rate is yet to be explicitly understood, which is complicated by the contrasting emission factors under different combustion conditions and their subsequent evolution in the atmosphere. Here we used a plume evolution chamber using ambient oxidants to simulate the evolution of residential solid fuel burning emissions under real-world solar radiation, and then to investigate the oxidation process of the emitted PAHs. Contrasting oxidation rate of PAHs was found to be influenced by particles with or without presence of substantial amount of black carbon (BC). In the flaming burning phase, which contained 46% of BC mass fraction and 8% of organic aerosol (OA) internally mixed with BC, the larger PAHs (with 4-7 rings) was rapidly oxidized 12% for every hour of evolution under solar radiation; however, the larger PAHs from smoldering phase tended to maintain unmodified during the evolution, when 95% of OA was externally mixed with only minor fraction of BC (<5%). This may be ascribed to the complex morphology of BC, allowing more exposure for the internally-mixed OA to the oxidants; in contrast with those externally-mixed OA which was prone to be coated by condensed secondary substances. This raises an important consideration about the particle mixing state in influencing the oxidation of PAHs, particularly the coating on PAHs which may extend their lifetime and environmental impacts.

Evolution of Aerosol Optical Properties from Wood Smoke in Real Atmosphere Influenced by Burning Phase and Solar Radiation.

Emissions of light-absorbing black carbon (BC) and organic aerosol (OA) from biomass burning are presented as complex mixtures, which introduce challenges in modeling their absorbing properties. In this study, we chose typical residential wood burning emission and used a novel designed chamber to investigate the early stage evolution of plumes from different burning phases under real ambient conditions. The detailed mixing state between BC and OA was evaluated, on the basis of which optical modeling was performed to achieve a closure of aerosol-absorbing properties. Intensive secondary OA (SOA) formation was observed under solar radiation. OA from flaming conditions showed a higher absorptivity than from smoldering conditions, as OA is mostly internally and externally mixed with BC, respectively. For flaming (smoldering), the imaginary refractive index of OA (kOA) was initially at 0.03 ± 0.01 (0.001) and 0.15 ± 0.02 (0.05 ± 0.02) at λ = 781 and 405 nm, respectively, with a half-decay time of 2-3 h in light but a <40% decrease under dark within 5 h. The production of less-absorbing SOA in the first 1-2 h and possible subsequent photobleaching of chromophores contributed to the decrease of kOA. The enhanced abundance but decreased absorptivity of coatings on BC resulted in a relatively maintainable absorptivity of BC-containing particles during evolution.

Ambient marine shipping emissions determined by vessel operation mode along the East China Sea.

Marine shipping emissions exert important air quality and climate impacts. This study characterized the ambient pollutants predominant by emissions from a variety of marine vessel types near the mid-latitude East China Sea. Two discernible primary shipping emissions were identified by factorization analysis on detailed mass spectra of organic aerosol (OA), as emissions in maneuvering and cruise, highly linked with NOx (and less oxidized OA, black carbon, BC) or CO (and more oxidized OA), respectively. Using radio-recorded quantities and activities of 3566 vessels mixed with slow and high-speed diesel engines, we found emission of NOx or BC per vessel was positively correlated with vessel speed, while CO emission peaked at moderate speed. The approach here based on vessel operation mode directly linked the vessel activities to ambient concentrations of pollutants from marine shipping emission, and may synthesize the complex vessel types in shipping emission inventory.

Comparison of air pollutants and their health effects in two developed regions in China during the COVID-19 pandemic.

Air pollution attributed to substantial anthropogenic emissions and significant secondary formation processes have been reported frequently in China, especially in Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD). In order to investigate the aerosol evolution processes before, in, and after the novel coronavirus (COVID-19) lockdown period of 2020, ambient monitoring data of six air pollutants were analyzed from Jan 1 to Apr 11 in both 2020 and 2019. Our results showed that the six ambient pollutants concentrations were much lower during the COVID-19 lockdown due to a great reduction of anthropogenic emissions. BTH suffered from air pollution more seriously in comparison of YRD, suggesting the differences in the industrial structures of these two regions. The significant difference between the normalized ratios of CO and NO2 during COVID-19 lockdown, along with the increasing PM2.5, indicated the oxidation of NO2 to form nitrate and the dominant contribution of secondary processes on PM2.5. In addition, the most health risk factor was PM2.5 and health-risked based air quality index (HAQI) values during the COVID-19 pandemic in YRD in 2020 were all lower than those in 2019. Our findings suggest that the reduction of anthropogenic emissions is essential to mitigate PM2.5 pollution, while O3 control may be more complicated.

Aqueous production of secondary organic aerosol from fossil-fuel emissions in winter Beijing haze.

Secondary organic aerosol (SOA) produced by atmospheric oxidation of primary emitted precursors is a major contributor to fine particulate matter (PM2.5) 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.

Real-time non-refractory PM1 chemical composition, size distribution and source apportionment at a coastal industrial park in the Yangtze River Delta region, China.

This study present real-time measurements of the chemical composition and particle number size distributions (PNSD) of submicron particulate matter (PM1) in winter at a coastal industrial park in the Yangtze River Delta region of China. Positive matrix factorization (PMF) analysis identified three PNSD factors and three organic aerosol (OA) factors. Contributions and potential source regions of these factors were investigated for four typical periods during the PM1 formation and dissipation process. Results show that the relative contributions from aged 250 nm- factor, fresh 35 nm- and 80 nm- factors were strongly affected by local fresh emissions and regional new particle formation. The non-refractory PM1 measured by Aerodyne aerosol chemical speciation monitor is indicative of the chemical composition of aged 250 nm-factor, but not fresh 35 nm- and 80 nm-factors. The contributions of NO3- and SO42- to NR-PM1 were largely dictated by whether the air mass trajectory went over the sea or the continent. NO3- was abundant (up to 44% of NR-PM1) in cold and dry continental air masses, while SO42- formation (up to 39% of NR-PM1) was preferred in humid and warm marine air masses. Among the three OA source factors, more-oxidized oxygenated OA (MO-OOA) was the most abundant OA factor (44-66% of total OA) throughout the entire field campaign, while an enhanced contribution of 39% from hydrocarbon-like OA (HOA) was observed prior to heavy pollution period. On average, secondary components SO42-, NO3-, NH4+, MO-OOA and less-oxidized oxygenated OA (LO-OOA) contributed 90 ± 7% of NR-PM1, while primary components HOA and Cl- accounted for the remaining 10 ± 7%.

Fast sulfate formation from oxidation of SO2 by NO2 and HONO observed in Beijing haze.

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 (SO2) emitted by coal combustion. There has been considerable debate regarding the mechanism for SO2 oxidation. Here we show evidence from field observations of a haze event that rapid oxidation of SO2 by nitrogen dioxide (NO2) and nitrous acid (HONO) takes place, the latter producing nitrous oxide (N2O). 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 SO2 by NO2, producing HONO which can in turn oxidize SO2 to yield N2O.This mechanism could provide an explanation for sulfate formation under some winter haze conditions.

Characterization of Size-Resolved Hygroscopicity of Black Carbon-Containing Particle in Urban Environment.

The hygroscopic properties of BC-containing particles (BCc) are important to determine their wet scavenging, atmospheric lifetime, and interactions with clouds. Such information is still lacking in the real world because of the challenges in isolating BCc from other aerosols to be directly characterized. In this study, the size-resolved chemical components of BCc including the refractory BC core and associated coatings were measured by a soot particle-aerosol mass spectrometer in suburban Nanjing. The size-resolved hygroscopicity parameter of BCc (κBCc) was obtained based on this full chemical characterization of BCc. We found increased inorganic fraction and more oxidized organic coatings with thicker coatings, which modified κBCc besides the determinant of particle size. The bulk κBCc was observed to range from 0.11 to 0.34. The size-resolved κBCc consistently showed minima at coated diameter (Dcoated) of 100 nm, parametrized as κ(x) = 0.28-0.35 × exp(-0.004 × x), x = Dcoated. Under critical supersaturations (SS) of 0.1% and 0.2%, the D50 values of BCc were 200 ± 20 and 135 ± 18 nm, respectively. On average 33 ± 16% and 59 ± 20% of BCc in number could be activated at SS = 0.1% and 0.2%, respectively. These results provide constraints on surface CCN sources for the light-absorbing BC-containing particles.

[Effects of Reduced Water and Diurnal Warming on Winter-Wheat Biomass and Soil Respiration].

Field experiments were conducted in winter wheat-growing season to investigate the effect of reduced water and diurnal warming on wheat biomass and soil respiration. The experimental treatments included the control (CK), 30% reduced water (W), diurnal warming (T, enhanced 2 degrees C), and the combined treatment (TW, 30% reduced water plus diurnal warming 2 degrees C). Soil respiration rate was measured using a static chamber-gas chromatograph technique. The results showed that in the winter wheat-growing season, compared to CK, T and TW treatments significantly increased shoot biomass by 46.0% (P = 0.002) and 19.8% (P = 0.032) during the elongation-booting stage, respectively. T and TW treatments also significantly increased the harvested shoot biomass by 19.8% (P = 0.050) and 34.6% (P = 0.028), respectively. On the other hand, W treatment had no significant effect on shoot biomass, and W, T, and TW treatments didn't significantly change the root biomass. T and W treatments had no significant effect on the mean respiration rate (MRR) of soil (P > 0.05). TW treatment significantly decreased soil MRR by 22.4% (P = 0.049). We also found T treatment decreased the temperature sensitivity coefficients of soil respiration (Q10). The results of our study suggested that compared to the single treatment (reduced water or diurnal warming), the combined treatment (reduced water plus diurnal warming) may have different effects on agroecosystem.

[Impacts of elevated ozone concentration on N2O emission from arid farmland].

To investigate the impact of elevated surface ozone (O3) concentration on nitrous oxide (N2O) emission from arid farmland, field experiments were carried out during winter-wheat and soybean growing seasons under the condition of simulating O3 concentrations, including free air (CK), 100 nL x L(-1) O3 concentration (T1), and 150 nL x L(-1) O3 concentration (T2). N2O emission fluxes were measured by static dark chamber-gas chromatograph method. The results showed that the accumulative amount of N2O (AAN) were decreased by 37.8% (P = 0.000 ) and 8.8% (P = 0.903 ) under T1 and T2 treatments, respectively, in the turning-green stage of winter wheat. In the elongation-booting stage, ANN were decreased by 15.0% (P = 0.217) and 39.1% (P = 0.000) under T1 and T2 treatments, respectively. ANN were decreased by 18.9% (P = 0.138) and 25.6% (P = 0.000) under T1 and T2 treatments, respectively, during the whole winter-wheat growing season. No significant impact of elevated O3 concentration on N2O emission from soil-soybean system was found due to the less rainfall during the soybean growing season, drought had a stronger stress on soybean than O3 concentration. The results of this study suggested that elevated O3 concentration could reduce N2O emission from arid farmland.

[Effects of conservation tillage on soil CO2 and N2O emission during the following winter-wheat season].

In order to study the effect of conservation tillage on soil CO2 and N2O emissions in the following crop-growing season, field experiments were conducted in the winter wheat-growing season. Four treatments were conventional tillage (T), no-tillage with no straw cover (NT), no-tillage with straw cover (NTS), and conventional tillage with straw incorporation (TS), respectively. The CO2 and N2O fluxes were measured using a static chamber-gas chromatograph technique. The results showed that in the following winter wheat-growing season, conservation tillage did not change the seasonal pattern of CO2 and N2O emission fluxes from soil, and had no significant effect on crop biomass. Conservation tillage significantly reduced the accumulative amount of CO2 and N2O. Compared with the T treatment, the accumulative amount of CO2 under TS, NT, and NTS treatments were reduced by 5.95% (P = 0.132), 12.94% (P = 0.007), and 13.91% (P = 0.004), respectively, and the accumulative amount of N2O were significantly reduced by 31.23% (P = 0.000), 61.29% (P = 0.000), and 33.08% (P = 0.000), respectively. Our findings suggest that conservation tillage significantly reduced CO2 and N2O emission from soil in the following winter wheat-growing season.