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.
It is a puzzle as to why more severe haze formed during the New Year Holiday in 2020 (NYH‐20), when China was in an unprecedented state of shutdown to contain the coronavirus (COVID‐19) outbreak, ...than in 2019 (NYH‐19). We performed a comprehensive measurement and modeling analysis of the aerosol chemistry and physics at multiple sites in China (mainly in Shanghai) before, during, and after NYH‐19 and NYH‐20. Much higher secondary aerosol fraction in PM2.5 were observed during NYH‐20 (73%) than during NYH‐19 (59%). During NYH‐20, PM2.5 levels correlated significantly with the oxidation ratio of nitrogen (r2 = 0.77, p < 0.01), and aged particles from northern China were found to impede atmospheric new particle formation and growth in Shanghai. A markedly enhanced efficiency of nitrate aerosol formation was observed along the transport pathways during NYH‐20, despite the overall low atmospheric NO2 levels.
Plain Language Summary
In China, there are multiple cases (e.g., the 2008 Summer Olympics in Beijing and the 2010 World Expo in Shanghai) when combustion‐related emissions (e.g., NOx) were actively, and successfully, reduced to transiently improve air quality. During the extended Chinese Lunar New Year holiday in 2020 (between 24 January and 10 February), whole China was in an unprecedented state of shutdown, because most people were contained in their homes to reduce the spread of the novel coronavirus disease (COVID‐19). Mobility, energy demand, and industrial output remained far below their normal levels. Nevertheless, widespread haze pollution still occurred over Eastern China. To elucidate haze formation mechanisms, we performed comprehensive and continuous measurements of aerosol chemistry and physics in and out of Shanghai before, during, and after the Chinese New Year Holiday in 2019 and 2020, respectively. We argue that the synergistic effects of long‐range transport and atmospheric chemistry leading to the efficient conversion of NOx to particulate nitrate were the key of haze formation during the Chinese New Year Holiday of the COVID‐19 outbreak in Shanghai.
Key Points
Higher concentrations and distinct compositions of aerosol particles were observed during the COVID‐19 shutdown
Fast formation of secondary inorganic aerosol contributed to high aerosol mass loading
Longer‐range, regional transport facilitated and enhanced particulate nitrate formation
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.
In this study, daily PM2.5 mass and chemical composition were measure in Lin’an Reginal Background Station, Yangzte River Delta, from March 1, 2018, to February 28, 2019. Organic matter (OM) was ...found to be the most dominant component in four seasons. The proportions of nitrate in PM2.5 presented dramatically lowest in warm seasons but highest in winter, indicating that NO3− was maily driven by thermodynamics. Regional transportation in winter plays a strong impact on PM2.5 concentration, which showed the highest average mass of 60.1 μg m−3. Sulfate occupied a significant portion of PM2.5 in summer (19%), followed by spring (17%), fall (15%), and winter (12%), respectively, suggesting photochemical processes may play a dominant role in the sulfate formation. Secondary inorganic aerosol (SIA) was the dominant component (70%) in the highest polluted periods (PM2.5 > 75 μg m−3), whereas OM decreased into the lowest fraction (22%) of PM2.5. Nitrate was the most important component in SIA in the highest polluted periods with regarding winter. Source apportionment results shown that winter haze was likely strongly dominated by SIA, which was mainly affected by air masses from the North China Plain and Shang-Hangzhou direction. PM2.5 is known to play an important role in sunlight absorption and reversing to human health, continuous observation on PM2.5 species in a background site can help us to evaluate the control policy, and promote our insights to lifetime, formation pathways, health effects of PM2.5.
•Daily PM2.5 mass and chemical composition were measure in Lin’an Reginal Background Station, Yangzte River Delta, from March 1, 2018, to February 28, 2019.•Organic matter (OM) was found to be the most dominant component in four seasons.•NO3− was mainly driven by thermodynamics.•Regional transportation in winter plays a strong impact on PM2.5 concentration.•Secondary inorganic aerosol (SIA) was the dominant component in the highest polluted periods.
The chemical complexity and toxicity of volatile organic compounds (VOCs) are primarily encountered through intensive anthropogenic emissions in suburban areas. Here, pollution characteristics, ...impacts on secondary pollution formation, and health risks were investigated through continuous in-field measurements from 1-30 June 2020 in suburban Nanjing, adjacent to national petrochemical industrial parks in China. On average, the total VOCs concentration was 34.47 ± 16.08 ppb, which was comprised mostly by alkanes (41.8%) and halogenated hydrocarbons (29.4%). In contrast, aromatics (17.4%) dominated the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) with 59.6% and 58.3%, respectively. Approximately 63.5% of VOCs were emitted from the petrochemical industry and from solvent usage based on source apportionment results, followed by biogenic emissions of 22.3% and vehicle emissions of 14.2%. Of the observed 46 VOC species, hexachlorobutadiene, dibromoethane, butadiene, tetrachloroethane, and vinyl chloride contributed as high as 98.8% of total carcinogenic risk, a large fraction of which was ascribed to the high-level emissions during ozone pollution episodes and nighttime. Therefore, the mitigation of VOC emissions from petrochemical industries would be an effective way to reduce secondary pollution and potential health risks in conurbation areas.
Intense new particle formation (NPF) events were observed in the coastal atmosphere
during algae growth and farming season at Xiangshan gulf of the east China coast. High
nucleation-mode iodine ...concentrations measured by ultra-performance liquid chromatography
coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) confirmed that
the NPF events were induced by iodine species. Our study provides important information
on iodine speciation, size distributions, and its role in NPF in the context of heavy air
pollution in China's coastal areas. For the first time, we identified 5 inorganic iodine
species, 45 organic iodine compounds (35 molecular formulas), and a group of
iodide–organic adducts in aerosols. The concentrations and size distributions of iodine
species down to 10 nm were measured during the iodine-induced NPF, continental NPF, and
non-NPF days at the coastal site and compared to those at an inland site. The iodine in
the above four aerosol sample types were characterized by iodate, aromatic iodine
compounds, iodoacetic acid or iodopropenoic acid, and iodide–organic adducts,
respectively. Iodide and organic iodine compounds were found in the nucleation-mode
particles; however, it is still not clear whether they contributed to nucleation or just
new particle growth. Wild algae, as well as farmed algae, could be an important NPF
source in China's coastal areas.
Coastal new particle formation (NPF) may be complicated due to the influence of both continental and marine air masses. Here we presented the result of particle number size distribution and NPF event ...measurements at a coastal industrial park of eastern China from 2018 to 2019. The highest nucleation-mode particle number concentration (daytime maximum: 4.9 × 103 cm−3) and NPF frequency (8% of the observation days) were observed in the continental-marine air masses that originated from North China Plain and traveled along the coastline before arriving at the coastal site. The formation rates of 2 nm particles (J2) at this coastal site are similar to those reported in the urban environments around the world, probably due to the influence of local industrial emission. Ion to total particle number concentration ratios in 2–7 nm and 7–20 nm were 1.5% and 12%, respectively, during the NPF periods. Neutral new particle formation pathway thus dominated over ion-mediated pathway at this coastal site. Our observation also showed that number concentration and formation rate of neutral new particles decreased monotonically with particle size, while those of charged new particles increased with particle size. Such difference points to additional formation and loss mechanisms of charged particles, such as ion-aerosol attachment and ion-ion recombination in the atmosphere. The behavior of appearance time-based growth rates, however, are similar for neutral and charged particles.
•Continental-marine air mass was favorable for new particle formation at the coastal site.•Formation rate of neutral particles decreased with particle size, while that of charged particles increased with size.•Neutral pathway dominated over ion-mediated pathway during the coastal NPF events.
Iodine-initiated new particle formation (I-NPF) has long been recognized in coastal hotspot regions. However, no prior work has studied the exact chemical composition of organic compounds and their ...role in coastal I-NPF. Here we present an important complementary study to the ongoing laboratory and field research on iodine nucleation in the coastal atmosphere. Oxidation and NPF experiments with vapor emissions from real-world coastal macroalgae were simulated in a bag reactor. On the basis of comprehensive mass spectrometry measurements, we reported for the first time a variety of volatile precursors and their oxidation products in gas and particle phases in such a highly complex system. Organic compounds overwhelmingly dominated over iodine in the new particle growth initiated by iodine species. The identity and transformation mechanisms of organic compounds were proposed in this study to provide a more complete story of coastal NPF from low-tide macroalgal emission.
p53 is the guardian of the genome integrity and the degradation of p53 protein is mediated by MDM2. Here we report that USP3 interacts with p53 and regulates p53 stability. Depletion of USP3 lead to ...accelerated degradation of p53 in normal cells thereby enhanced cell proliferation and transformation. Reconstitution of wildtype USP3, but not the USP3 C168S mutant, restored the stability of p53 protein and inhibited cell proliferation and transformation. These findings suggest that USP3 is an important regulator of p53 and regulates normal cell transformation.
•USP3 is a deubiquitinase for p53 and antagonizes Mdm2.•USP3 stabilizes p53 protein under normal condition.•Loss of USP3 accelerates cell proliferation and transformation.
Restrictions on emission controls were implemented in China to cope with the outbreak of the Coronavirus Disease 2019 (COVID-19), providing a chance to study the impacts of anthropogenic emissions on ...air quality. Subsequently, three-year measurements of PM2.5 chemical composition and light absorption were conducted in a typical megacity (Suzhou) of the Yangtze River Delta in China from 2019 to 2021. The annual observation period was divided into four different stages: Normal Days, Chinese New Year, Lockdown, and Work Resumption. Our results show that the concentrations of PM2.5 composition (e.g., SO42−, NO3−, OC, and EC) and gas species (e.g., SO2, NO2, and CO) gradually decreased from 2019 to 2021, associated with emission reduction. During the four stages, the COVID-19 lockdown period had the lowest concentrations of PM2.5, indicating that strict emission control could significantly improve the air quality. The significant increase in O3 during the COVID-19 lockdown period is likely due to the reduced NO emission from the traffic. The Normal Days in 2020 had the highest mass loadings of SO42−, NO3−, NH4+, OC, and EC, while the mass concentrations of SO42−, NO3−, NH4+, Cl−, and Na+ in the Lockdown were the lowest. Meanwhile, aerosol light absorption has decreased yearly, and significant decreases in light absorption were observed during the COVID-19 lockdown. The high values of Absorption Ångström exponent (AAE) observed in Suzhou (ranging from 1.3 to 1.4), indicated that brown carbon played critical contributions to the light absorption. The mass concentration and fraction of fuel fossil were significantly higher than that of biomass burning during the entire campaign. The remarkable decline of fuel fossil BC during the COVID-19 lockdown can be attributed to the closure of factories and the reduction of vehicle emissions. The potential contribution source function analysis suggests a notable regional variation in the sources of fossil fuel and biomass combustion. Our results highlight that strict emission control could provide a positive direction for air pollution mitigation campaigns.
•Strict emission control is effective in mitigating air pollution (i.e., light absorption and concentration of PM2.5) in the YRD region.•BrC accounted for 37% of the aerosol absorption at 370 nm during the COVID-19 lockdown in 2020.•The contribution of fossil fuel sources in BC was significantly higher than that of biomass burning pre and post the COVID-19 lockdown.
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