Enhanced secondary pollution offset reduction of primary emissions during COVID-19 lockdown in China

National Science Review, Journal Year: 2020, Volume and Issue: 8(2)

Published: June 16, 2020

To control the spread of 2019 novel coronavirus (COVID-19), China imposed nationwide restrictions on movement its population (lockdown) after Chinese New Year 2020, leading to large reductions in economic activities and associated emissions. Despite such decreases primary pollution, there were nonetheless several periods heavy haze pollution eastern China, raising questions about well-established relationship between human air quality. Here, using comprehensive measurements modeling, we show that during COVID lockdown was driven by enhancements secondary pollution. In particular, NOx emissions from transportation increased ozone nighttime NO3 radical formation, these increases atmospheric oxidizing capacity turn facilitated formation particulate matter. Our results, afforded tragic natural experiment COVID-19 pandemic, indicate mitigation depends upon a coordinated balanced strategy for controlling multiple pollutants.

Language: Английский

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The acidity of atmospheric particles and clouds

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(8), P. 4809 - 4888

Published: April 24, 2020

Abstract. Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, acidity condensed phases (aerosol particles, cloud water, and fog droplets) governs phase partitioning semivolatile gases such HNO3, NH3, HCl, organic acids bases well chemical reaction rates. It has implications for atmospheric lifetime pollutants, deposition, human health. Despite its fundamental role in processes, only recently this field seen growth number studies on particle acidity. Even with growth, many fine-particle pH estimates must be based thermodynamic model calculations since no operational techniques exist direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained limited spatial temporal coverage. Clouds fogs also generally acidic, to lesser degree than have range that quite sensitive anthropogenic emissions sulfur nitrogen oxides, ambient ammonia. Historical measurements indicate droplet changed recent decades response controls emissions, while trend data aerosol may relatively constant due nature key buffering particles. This paper reviews synthesizes current state knowledge phases, specifically droplets. includes recommendations estimating standard nomenclature, synthesis observations, new local global scale.

Language: Английский

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Estimating PM_2.5 Concentrations in the Conterminous United States Using the Random Forest Approach

Environmental Science & Technology, Journal Year: 2017, Volume and Issue: 51(12), P. 6936 - 6944

Published: May 23, 2017

To estimate PM2.5 concentrations, many parametric regression models have been developed, while nonparametric machine learning algorithms are used less often and national-scale rare. In this paper, we develop a random forest model incorporating aerosol optical depth (AOD) data, meteorological fields, land use variables to daily 24 h averaged ground-level concentrations over the conterminous United States in 2011. Random forests an ensemble method that provides predictions with high accuracy interpretability. Our results achieve overall cross-validation (CV) R2 value of 0.80. Mean prediction error (MPE) root mean squared (RMSPE) for 1.78 2.83 μg/m3, respectively, indicating good agreement between CV observations. The our is similar those reported previous studies using neural networks or on both national regional scales. addition, incorporation convolutional layers terms nearby measurements increase by ∼0.02 ∼0.06, their significant contributions accuracy. A pair different variable importance measures indicate layer AOD values among most-important predictor training process.

Language: Английский

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Persistent Heavy Winter Nitrate Pollution Driven by Increased Photochemical Oxidants in Northern China

Environmental Science & Technology, Journal Year: 2020, Volume and Issue: 54(7), P. 3881 - 3889

Published: March 3, 2020

Nitrate is an increasingly important component of fine particulate matter (PM2.5) during winter in northern China. Past emission control has been ineffective reducing nitrate. Here, we use extensive observations and a model with state-of-the-art nitrogen chemistry to identify the key factors that nitrate formation heavily polluted North China Plain (NCP). In contrast previous view weak photochemistry, show O3 OH productions are sufficiently high facilitate fast gas-phase heterogeneous conversion NOX over NCP. Increasing from higher precursor levels ROX cycling accelerate generation heavy pollution. We find 31.8% reduction emissions 2010 2017 NCP lowers surface by only 0.2% even increases some areas. This mainly due increase (by ∼30%), which subsequently increased efficiency HNO3 38.7%). Future strategies for haze should also aim lower photochemical oxidants, via larger synchronized VOCs reduction, overcome effects nonlinear photochemistry aerosol chemical feedback.

Language: Английский

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Changes in Aerosol Chemistry From 2014 to 2016 in Winter in Beijing: Insights From High‐Resolution Aerosol Mass Spectrometry

Journal of Geophysical Research Atmospheres, Journal Year: 2018, Volume and Issue: 124(2), P. 1132 - 1147

Published: Dec. 22, 2018

Abstract Air quality has been continuously improved in recent years Beijing, yet severe haze episodes still frequently occur winter. Here we deployed an Aerodyne high‐resolution aerosol mass spectrometer two winter seasons during the same period to investigate changes chemistry from 2014 2016 Beijing. Compared 2014, submicron (PM 1 ) species showed ubiquitous increases concentrations by 10–130% 2016, of which nitrate largest increase among all leading a much higher NO 3 /SO 4 ratio (1.36 ± 0.90) than (0.72 0.59). This result highlights increasing role particulate matter pollution Aerosol composition and size distributions also changed significantly. Secondary inorganic elevated contributions ~10% associated with corresponding decreases organic (OA). Positive matrix factorization OA illustrated significant both primary emissions secondary production. While cooking decreased substantially 25% 15% contribution biomass burning slightly increased instead. Although contributed similarly winters (49% vs. 53%), observed (~50%) photochemically related oxygenated oxidized OA, oxygen‐to‐carbon ratios indicating enhanced photochemical production 2016. Aqueous‐phase however was relatively similar winters. Further analysis demonstrated that varied differently across different relative humidity levels.

Language: Английский

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Rapid transition in winter aerosol composition in Beijing from 2014 to 2017: response to clean air actions

Atmospheric chemistry and physics, Journal Year: 2019, Volume and Issue: 19(17), P. 11485 - 11499

Published: Sept. 12, 2019

Abstract. The clean air actions implemented by the Chinese government in 2013 have led to significantly improved quality Beijing. In this work, we combined situ measurements of chemical components submicron particles (PM1) Beijing during winters 2014 and 2017 a regional transport model investigate impact on aerosol chemistry quantify relative contributions anthropogenic emissions, meteorological conditions, changes composition from 2017. We found that average PM1 concentration winter decreased 49.5 % (from 66.2 33.4 µg m−3). Sulfate exhibited much larger decline than nitrate ammonium, which rapid transition sulfate-driven nitrate-driven pollution wintertime. Organic (OA), especially coal combustion OA, black carbon also showed large decreasing rates, indicating effective emission control biomass burning. sulfate contribution increased fraction were highly consistent with faster reductions sulfur dioxide (SO2) due phasing out compared reduction nitrogen oxides emissions estimated bottom-up inventory. simulations these estimates reproduced suggested reduced its surrounding regions played dominant role. variations conditions contributed less 2014–2017 emissions. Finally, speculated precursor possibly altered formation mechanisms based ambient observations. observed explosive growth at humidity (RH) greater 50 was delayed higher RH 70 2017, likely caused suppressed through heterogeneous reactions decrease SO2 Thermodynamic concentrations lowered water content, particle acidity, ammonium fraction. results study demonstrate response stringent identify are major driver, could help further guide strategies China.

Language: Английский

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Effect of changing NO<sub><i>x</i></sub> lifetime on the seasonality and long-term trends of satellite-observed tropospheric NO<sub>2</sub> columns over China

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(3), P. 1483 - 1495

Published: Feb. 7, 2020

Abstract. Satellite observations of tropospheric NO2 columns are extensively used to infer trends in anthropogenic emissions nitrogen oxides (NOx≡NO+NO2), but this may be complicated by NOx lifetime. Here we use 2004–2018 from the Ozone Monitoring Instrument (OMI) satellite-based instrument (QA4ECV and POMINO v2 retrievals) examine seasonality over central–eastern China, interpret results with GEOS-Chem chemical transport model. The show a factor 3 increase summer winter, which explain as reflecting longer lifetime winter than (21 h versus 5.9 2017). 2005–2018 OMI closely follow Multi-resolution Emission Inventory for China (MEIC), rise 2005–2011 period 25 % decrease since. We find no significant trend summer, supporting emission reported MEIC. is steeper entire period, attribute at lower emissions. Half sink N2O5 hydrolysis, counterintuitively becomes more efficient due less titration ozone night. formation organic nitrates also an increasing volatile compounds (VOCs) do not.

Language: Английский

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Contribution of Wildland-Fire Smoke to US PM_2.5 and Its Influence on Recent Trends

Environmental Science & Technology, Journal Year: 2019, Volume and Issue: 53(4), P. 1797 - 1804

Published: Jan. 25, 2019

Seasonal-mean concentrations of particulate matter with diameters smaller than 2.5 μm (PM2.5) have been decreasing across the United States (US) for several decades, large reductions in spring and summer eastern US. In contrast, summertime-mean PM2.5 western US has not significantly decreased. Wildfires, a source summertime US, increasing frequency burned area recent decades. Increases extreme events attributable to wildland fires observed wildfire-prone regions, but it is unclear how these increases impact trends seasonal-mean PM2.5. Using two distinct methods, (1) interpolated surface observations combined satellite-based smoke plume estimates (2) GEOS-Chem chemical transport model (CTM), we identify (2006-2016) smoke, nonsmoke, total We observe significant decreases nonsmoke influenced find summer-mean fire-prone although are statistically due interannual variability abundance smoke. These results indicate that without influence fires, would expect improvements fine particle pollution likely weaker those

Language: Английский

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The global impacts of COVID-19 lockdowns on urban air pollution

Elementa Science of the Anthropocene, Journal Year: 2021, Volume and Issue: 9(1)

Published: Jan. 1, 2021

The coronavirus-19 (COVID-19) pandemic led to government interventions limit the spread of disease which are unprecedented in recent history; for example, stay at home orders sudden decreases atmospheric emissions from transportation sector. In this review article, current understanding influence emission reductions on pollutant concentrations and air quality is summarized nitrogen dioxide (NO2), particulate matter (PM2.5), ozone (O3), ammonia, sulfur dioxide, black carbon, volatile organic compounds, carbon monoxide (CO). first 7 months following onset pandemic, more than 200 papers were accepted by peer-reviewed journals utilizing observations ground-based satellite instruments. Only about one-third literature incorporates a specific method meteorological correction or normalization comparing data lockdown period with prior reference despite importance doing so interpretation results. We use stringency index (SI) as an indicator severity measures show how key pollutants change SI increases. observed decrease NO2 increasing general agreement inventories that account lockdown. Other compounds such O3, PM2.5, CO also broadly covered. Due chemistry O3 PM2.5 concentrations, their responses may not be linear respect primary pollutants. At most sites, we found increased, whereas decreased slightly, SI. Changes other understudied. highlight future research needs emerging sets preview state atmosphere world targeted permanent emissions. Finally, emphasize need effects meteorology, trends, when determining concentrations.

Language: Английский

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Multiphase Oxidation of Sulfur Dioxide in Aerosol Particles: Implications for Sulfate Formation in Polluted Environments

Environmental Science & Technology, Journal Year: 2021, Volume and Issue: 55(8), P. 4227 - 4242

Published: March 24, 2021

Atmospheric oxidation of sulfur dioxide (SO2) forms sulfate-containing aerosol particles that impact air quality, climate, and human ecosystem health. It is well-known in-cloud SO2 frequently dominates over gas-phase on regional global scales. Multiphase involving particles, fog, cloud droplets has been generally thought to scale with liquid water content (LWC) so multiphase would be negligible for due their low LWC. However, recent field evidence, particularly from East Asia, shows fast sulfate formation prevails in cloud-free environments are characterized by high loadings. By assuming the kinetics chemistry most atmospheric models do not capture this phenomenon. Therefore, blossomed past decade, many processes proposed bridge difference between modeled observed mass This review summarizes advances fundamental understanding SO2, a focus environmental conditions affect rate, experimental challenges, mechanisms results individual reaction pathways, future research directions. Compared dilute conditions, paper highlights differences arise at molecular level extremely solute strengths present particles.

Language: Английский

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