scholarly journals Worsening urban ozone pollution in China from 2013 to 2017 – Part 2: The effects of emission changes and implications for multi-pollutant control

2020 ◽  
Vol 20 (11) ◽  
pp. 6323-6337 ◽  
Author(s):  
Yiming Liu ◽  
Tao Wang
Keyword(s):  
Urban Areas ◽  
Nox Reduction ◽  
Nox Emission ◽  
Pollutant Emissions ◽  
Photolysis Rates ◽  
Ambient Concentrations ◽  
Reduction Of Nox ◽  
Reactive Gases ◽  
Aerosol Effects ◽  
Surface O3

Abstract. The Chinese government launched the Air Pollution Prevention and Control Action Plan in 2013, and various stringent measures have since been implemented, which have resulted in significant decreases in emissions and ambient concentrations of primary pollutants such as SO2, NOx, and particulate matter (PM). However, surface ozone (O3) concentrations have still been increasing in urban areas across the country. In a previous analysis, we examined in detail the roles of meteorological variation during 2013–2017 in the summertime surface O3 trend in various regions of China. In this study, we evaluated the effect of changes in multi-pollutant emissions from anthropogenic activities on O3 levels during the same period by using an up-to-date regional chemical transport model (WRF-CMAQ) driven by an interannual anthropogenic emission inventory. The Community Multiscale Air Quality (CMAQ) model was improved with regard to heterogeneous reactions of reactive gases on aerosol surfaces, which led to better model performance in reproducing the ambient concentrations of those gases. The model simulations showed that the maximum daily 8 h average (MDA8) O3 mixing ratio in urban areas increased by 0.46 ppbv per year (ppbv a−1) (p=0.001) from 2013 to 2017. In contrast, a slight decrease in MDA8 O3 by 0.17 ppbv a−1 (p=0.005) in rural areas was predicted, mainly attributable to the NOx emission reduction. The effects of changes in individual pollutant emissions on O3 were also simulated. The reduction of NOx emission increased the O3 levels in urban areas due to the nonlinear NOx and volatile organic compound (VOC) chemistry and decreasing aerosol effects; the slight increase in VOC emissions enhanced the O3 levels; the reduction of PM emissions increased the O3 levels by enhancing the photolysis rates and reducing the loss of reactive gases on aerosol surfaces; and the reduction of SO2 emissions resulted in a drastic decrease in sulfate concentrations, which increased O3 through aerosol effects. In contrast to the unfavorable effect of the above changes in pollutant emissions on efforts to reduce surface O3, the reduction of CO emissions did help to decrease the O3 level in recent years. The dominant cause of increasing O3 due to changes in anthropogenic emissions varied geographically. In Beijing, NOx and PM emission reductions were the two largest causes of the O3 increase; in Shanghai, the reduction of NOx and increase in VOC emissions were the two major causes; in Guangzhou, NOx reduction was the primary cause; in Chengdu, the PM and SO2 emission decreases contributed most to the O3 increase. Regarding the effects of decreasing concentrations of aerosols, the drop in heterogeneous uptake of reactive gases – mainly HO2 and O3 – was found to be more important than the increase in photolysis rates. The adverse effect of the reductions of NOx, SO2, and PM emissions on O3 abatement in Beijing, Shanghai, Guangzhou, and Chengdu would have been avoided if the anthropogenic VOCs emission had been reduced by 24 %, 23 %, 20 %, and 16 %, respectively, from 2013 to 2017. Our analysis revealed that the NOx reduction in recent years has helped to contain the total O3 production in China. However, to reduce O3 levels in major urban and industrial areas, VOC emission controls should be added to the current NOx-SO2-PM policy.

scholarly journals Worsening urban ozone pollution in China from 2013 to 2017 – Part 2: The effects of emission changes and implications for multi-pollutant control

2020 ◽  
Author(s):  
Yiming Liu ◽  
Tao Wang
Keyword(s):  
Urban Areas ◽  
Nox Reduction ◽  
Nox Emission ◽  
Pollutant Emissions ◽  
Anthropogenic Emission ◽  
Photolysis Rates ◽  
Ambient Concentrations ◽  
Reduction Of Nox ◽  
Reactive Gases ◽  
Aerosol Effects

Abstract. The Chinese government launched the Air Pollution Prevention and Control Action Plan in 2013, and various stringent measures have since been implemented, which have resulted in significant decreases in emissions and ambient concentrations of primary pollutants such as SO2, NOx, and particulate matter (PM). However, surface ozone (O3) concentrations have still been increasing in urban areas across the country. In a previous analysis, we examined in detail the roles of meteorological variation during 2013–2017 in the summertime surface O3 trend in various regions of China. In this study, we evaluated the effect of changes in multi-pollutant emissions from anthropogenic activities on O3 concentrations during the same period, by using an up-to-date regional chemical transport model (WRF-CMAQ) driven by an interannual anthropogenic emission inventory. The CMAQ model was improved with regard to heterogeneous reactions of reactive gases on aerosol surfaces, which led to better model performance in reproducing the ambient concentrations of those gases. The model simulations showed that the maximum daily 8-hour average (MDA8) O3 concentration in urban areas increased by 0.46 ppbv per year (ppbv a-1) (p = 0.001) from 2013 to 2017. In contrast, a slight decrease in MDA8 O3 concentrations by 0.17 ppbv a-1 (p = 0.005) in rural areas was predicted, mainly attributable to the NOx emission reduction. The effects of changes in individual pollutant emissions on O3 were also simulated. The reduction of NOx emission increased the O3 concentration in urban areas due to the non-linear NOx-volatile organic compound (VOC) chemistry and decreasing aerosol effects; the slight increase in VOCs emissions enhanced the O3 concentrations; the reduction of PM emissions increased the O3 concentrations by enhancing the photolysis rates and reducing the loss of reactive gases on aerosol surfaces; and the reduction of SO2 emissions resulted in a drastic decrease in sulfate concentrations, which increased the O3 concentrations through aerosol effects. In contrast to the unfavorable effect of the above changes in pollutant emissions on efforts to reduce surface concentrations of O3, the reduction of CO emissions did help to decrease the O3 concentrations in recent years. The dominant cause of increasing O3 concentrations due to changes in anthropogenic emission varied geographically. In Beijing, NOx and PM emission reductions were the two largest causes of the O3 increase; in Shanghai, the reduction of NOx and increase in VOC emissions were the two major causes; in Guangzhou, NOx reduction was the primary cause; and in Chengdu, the PM and SO2 emission decreases contributed most to the O3 concentration increase. Regarding the effects of decreasing concentrations of aerosols, the drop in heterogeneous uptake of reactive gases – mainly HO2 and O3 – was found to be more important than the increase in photolysis rates. The adverse effect of the reductions of NOx, SO2, and PM emissions on O3 abatement in Beijing, Shanghai, Guangzhou, and Chengdu would have been avoided if the anthropogenic VOCs emission had been reduced by 24 %, 23 %, 20 %, and 16 %, respectively, from 2013 to 2017. Our analysis revealed that the NOx reduction in recent years has helped to contain the total O3 production in China. However, to reduce O3 concentrations in major urban and industrial areas, VOCs emissions control should be added to the current NOx-SO2-PM policy.

scholarly journals Measurement and model analyses of the ozone variation during 2006 to 2015 and its response to emission change in megacity Shanghai, China

2019 ◽  
Author(s):  
Jianming Xu ◽  
Xuexi Tie ◽  
Wei Gao ◽  
Yanfen Lin ◽  
Qingyan Fu
Keyword(s):  
Control Strategy ◽  
Fine Particles ◽  
Action Plan ◽  
Nox Reduction ◽  
Nox Emission ◽  
Transition Regime ◽  
Local Dispersion ◽  
Clean Air ◽  
Reduction Of Nox ◽  
Emission Change

Abstract. The fine particles (PM2.5) in China decrease significantly in recent years as a result of the implement of Chinese Clean Air Action Plan since 2013, while the O3 pollution is getting worse, especially in megacities such as Beijing and Shanghai. Better understanding the elevated O3 pollution in Chinese megacities and its response to emission change is important for developing an effective emission control strategy in future. In this study, we analyze the significant increasing trend of O3 concentration from 2006 to 2015 in the megacity Shanghai with the variability of 1–1.3 ppbv yr-1. It is likely attributed to the notable reduction of NOx concentration with the decreasing rate of 1.86–2.15 ppbv yr-1 accompanied with the little change of VOCs during the same period excluding the weak trends of meteorological impacts on local dispersion (wind speed), regional transport (wind direction) and O3 photolysis (solar radiation). It is further illustrated by using a state of the art regional chemical/dynamical model (WRF-Chem) to explore the O3 variation response to the reduction of NOx emission in Shanghai. The control experiment conducted in September of 2009 shows very excellent performance for O3 and NOx simulations including both the spatial distribution pattern, and the day by day variation by comparing with 6 in-situ measurements from MIRAGE-shanghai field campaign. Sensitive experiments with 30 % reduction of NOx emission from 2009 to 2015 in Shanghai estimated by Shanghai Environmental Monitoring Center shows that the calculated O3 concentrations exhibit obvious enhancement by 4–7 ppbv in urban zones with the increasing variability of 0.96–1.06 ppbv yr-1, which is well consistent with the observed O3 trend as a result of the strong VOC-limited condition for O3 production. The large reduction of NOx combined with less change of VOCs during the past ten years promotes the O3 production in Shanghai to move towards NOx-limited regime. Further analysis of WRF-Chem experiments and O3 isopleths diagram suggests that the O3 production in downtown is still under VOC-limited regime after 2015 despite of the remarkable NOx reduction, while moves to the transition regime between NOx-limited and VOC-limited in sub-urban zones. Supposing the insignificant VOCs variation persists, the O3 concentration in downtown would keep increasing till 2020 with the further 20 % reduction of NOx emission after 2015 estimated by Shanghai Clean Air Action Plan. While there are less O3 change in other regions where the O3 production is not under VOC-limited regime. The O3 production in Shanghai will switch from VOC-limited to NOx-limited regime after 2020 except downtown area which is likely close to the transition regime. As a result the O3 concentration will decrease by 2–3 ppbv in sub-urban zones, and more than 4 ppbv in suburb response to 20 % reduction of NOx emission after 2020, whereas is not sensitive to both NOx and VOCs changes in downtown. This result reveals that the control strategy of O3 pollution is a very complex process, and needs to be carefully studied.

Humid Air NOx Reduction Effect on Liquid Fuel Combustion

2004 ◽  
Vol 126 (1) ◽  
pp. 69-74 ◽  
Author(s):  
A. G. Chen ◽  
Daniel J. Maloney ◽  
William H. Day
Keyword(s):  
Liquid Fuel ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Substantial Reduction ◽  
Combustion Process ◽  
Pollutant Emissions ◽  
Humid Air ◽  
Wide Range ◽  
Reduction Of Nox ◽  
Reduction Effect

An experimental investigation was carried out at DOE NETL on the humid air combustion process using liquid fuel to determine the effects of humidity on pollutant emissions and flame stability. Tests were conducted at pressures of up to 100 psia (690 kPa), and a typical inlet air temperature of 860°F (733 K). The emissions and RMS pressures were documented for a relatively wide range of flame temperature from 2440-3090°F (1610–1970 K) with and without added humidity. The results show more than 90% reduction of NOx through 10% humidity addition to the compressed air compared with the dry case at the same flame temperature. The substantial reduction of NOx is due to a shift in the chemical mechanisms and cannot be explained by flame temperature reduction due to added moisture since the comparison was made for the same flame temperature.

scholarly journals Quantifying errors in surface ozone predictions associated with clouds over CONUS: A WRF-Chem modeling study using satellite cloud retrievals

2017 ◽  
Author(s):  
Young-Hee Ryu ◽  
Alma Hodzic ◽  
Jerome Barre ◽  
Gael Descombes ◽  
Patrick Minnis
Keyword(s):  
Urban Areas ◽  
Surface Ozone ◽  
Horizontal Resolution ◽  
Cumulus Parameterization ◽  
Weather Research And Forecasting ◽  
Model Errors ◽  
Microphysics Scheme ◽  
Photolysis Rates ◽  
The Right ◽  
Surface O3

Abstract. Clouds play a key role in radiation and hence O3 photochemistry by modulating photolysis rates and light-dependent emissions of biogenic volatile organic compounds (BVOCs). It is not well known, however, how much error in O3 predictions can be directly attributed to that in cloud predictions. This study applies the Weather Research and Forecasting with Chemistry (WRF-Chem) at 12 km horizontal resolution with the Morrison microphysics and Grell 3D cumulus parameterization to quantify uncertainties in summertime surface O3 predictions associated with the cloudiness over contiguous United States (CONUS). To evaluate the model's own clouds and to restrain the growth of model errors, the model is driven by reanalysis atmospheric data and reinitialized every 2 days. In sensitivity simulations, cloud fields used for photochemistry are corrected based on satellite cloud retrievals. The results show that WRF-Chem predicts about 55 % of clouds in the right locations and generally underpredicts cloud optical depths. These errors in cloud predictions can lead up to 60 ppb overestimation in hourly surface O3 concentrations on some days. The average difference in summertime surface O3 concentrations derived from the modeled clouds and satellite clouds ranges from 1 to 6 ppb for the 8-h average O3 over CONUS. This represents up to ~ 40 % of the total 8-h average O3 bias under cloudy conditions in the tested model version, and the results are robust with respect to the choice of the microphysics scheme. Surface O3 concentrations are sensitive to cloud errors mainly through the calculation of photolysis rates (for ~ 80 %), and to a lesser extent to light-dependent BVOC emissions. The sensitivity of surface O3 to satellite-based cloud corrections is about 2 times larger in VOC-limited than NOX-limited regimes. Our results suggest that the benefits of accurate predictions of cloudiness would be significant in VOC-limited regions which are typical of urban areas.

Humid Air NOx Reduction Effect on Liquid Fuel Combustion

2002 ◽  
Author(s):  
Alexander G. Chen ◽  
Daniel J. Maloney ◽  
William H. Day
Keyword(s):  
Liquid Fuel ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Substantial Reduction ◽  
Combustion Process ◽  
Pollutant Emissions ◽  
Humid Air ◽  
Wide Range ◽  
Reduction Of Nox ◽  
Reduction Effect

An experimental investigation was carried out at DOE NETL on the humid air combustion process using liquid fuel to determine the effects of humidity on pollutant emissions and flame stability. Tests were conducted at pressures of up to 100 psia (690 kPa), and a typical inlet air temperature of 860 °F (733 K). The emissions and RMS pressures were documented for a relatively wide range of flame temperature from 2440–3090 °F (1610 − 1970 K) with and without added humidity. The results show more than 90 percent reduction of NOx through 10 percent humidity addition to the compressed air compared with the dry case at the same flame temperature. The substantial reduction of NOx is due to a shift in the chemical mechanisms and cannot be explained by flame temperature reduction due to added moisture since the comparison was made for the same flame temperature.

Worsening urban ozone pollution in China from 2013 to 2017: The roles of meteorology and anthropogenic emission

2020 ◽  
Author(s):  
Yiming Liu ◽  
Tao Wang
Keyword(s):  
Urban Areas ◽  
Biogenic Emissions ◽  
Anthropogenic Emission ◽  
Ozone Pollution ◽  
The Past ◽  
Ozone Concentrations ◽  
Photolysis Rates ◽  
Aerosol Effects ◽  
Vocs Emission ◽  
Ozone Levels

<p>China has suffered from increasing levels of ozone pollution in urban areas despite the implementation of various stringent emission reduction measures since 2013. In this study, we conducted numerical experiments with an up-to-date regional chemical transport model to assess the roles of changes in meteorology and anthropogenic emission in summer ozone variations from 2013 to 2017 over China. The model can faithfully reproduce the observed meteorological parameters and air pollutant concentrations and capture the increasing trend in the surface maximum daily 8-hour average (MDA8) ozone (O<sub>3</sub>) from 2013 to 2017. An increase of 0.46 ppbv a<sup>-1</sup> (p=0.001) and a slight decrease of 0.17 ppbv a<sup>-1</sup> (p=0.005) in MDA8 O<sub>3</sub> levels were simulated from 2013 to 2017 in urban and rural areas, respectively. The meteorological influence on the ozone trend varied by region and by year and could be comparable with or even larger than the impact of changes in anthropogenic emissions. The variation in biogenic emissions during summer varied across regions and was mainly affected by temperature. China’s midlatitude areas (25°N to 40°N) experienced a significant decrease in MDA8 O<sub>3</sub> due to a decline in biogenic emissions, while higher temperatures in northern (north of 40°N) and southern (south of 25°N) China after 2013 led to an increase in MDA8 O<sub>3</sub> concentrations via an increase in biogenic emissions. We assessed the effects of changes in individual meteorological factors on ozone levels from 2013 to 2017. The results show that the wind field change made a significant contribution to the increase in surface ozone over China by transporting the ozone downward from the upper troposphere and the lower stratosphere. The long-range transport of ozone and its precursors outside the modeling domain also contributed to the increase in MDA8 O<sub>3</sub> on the Tibetan Plateau. The effects of changes in individual pollutant emissions on ozone were simulated. The reduction of NO<sub>x</sub> emission increased ozone in urban areas due to non-linear NO<sub>x</sub>-VOCs chemistry and decreased aerosol effects; the slight increase in VOCs emission enhanced ozone levels; the reduction of particulate matter(PM) emission increased ozone concentrations by enhancing the photolysis rates and reducing the loss of reactive gases on aerosol surfaces; the reduction of SO<sub>2</sub> emission resulted in a drastic decrease in sulfate concentrations which increase ozone levels through the aerosol effects. In contrast, the reduction of CO emissions helped decrease ozone levels in the past years. On the effects of decreasing levels of aerosol, the drop in heterogeneous uptake of reactive gasses, mainly HO<sub>2</sub> and O<sub>3</sub>, was found to be more important than the increase in photolysis rates. The adverse effect on ozone of the reductions of NO<sub>x</sub>, SO<sub>2</sub> and PM emissions would have been avoided with ~20% reduction of VOCs emission from 2013 to 2017. Our analysis revealed that the NO<sub>x</sub> reduction in the past years has helped to contain the total ozone production in China. However, in order to decrease ozone concentrations in major urban and industrial areas, VOCs emission control should be added to the current NO<sub>x</sub>-SO<sub>2</sub>-PM policy.</p>

scholarly journals Solid Selective Catalytic Reduction: A Promising Approach towards Reduction of NOx Emission from Exhaust of CI Engines

2021 ◽  
Vol 20 (4) ◽  
Author(s):  
M. K. Yadav ◽  
A. K. Srivastava
Keyword(s):  
Diesel Engine ◽  
Selective Catalytic Reduction ◽  
Diesel Engines ◽  
Urban Areas ◽  
Catalytic Reduction ◽  
Nox Emission ◽  
Engine Exhaust ◽  
Diesel Engine Exhaust ◽  
Reduction Of Nox ◽  
Ci Engines

The rising rate of pollution in urban areas has become a worldwide concern in recent years. Diesel engines are considered one of the largest contributors to environmental pollution caused by exhaust emissions, and they are responsible for several health problems as well. Diesel engines contain carbon monoxide, carbon dioxide, unburned hydrocarbons, and oxides of nitrogen. The reduction of Nitric oxides (NOx) emission from diesel engine exhaust is currently being researched by automotive manufacturers. After much research, selective catalytic reduction (SCR) technology was discovered to be effective in reducing nitrogen oxide emission from diesel engine exhaust. This paper is an attempt to explore the problems associated with the use of selective catalytic reduction (SCR) and compares selective catalytic reduction (SCR) with the latest technology named solid selective catalytic reduction (SSCR) for efficient reduction of NOx emission from the exhaust of diesel engines. The issue of contamination, malfunctioning, and freezing of diesel exhaust fluid (DEF) at low temperatures are the major problems associated with the application of SCR. It is observed that by controlling the quantity of ammonia slip, SSCR can give better performance in the reduction of NOx emission from the exhaust of diesel engines.

Reduction of NOx in a Regenerative Industrial Furnace With the Addition of Methanol in the Fuel

2004 ◽  
Vol 126 (2) ◽  
pp. 159-165 ◽  
Author(s):  
Q. Jiang ◽  
C. Zhang ◽  
J. Jiang
Keyword(s):  
Mixture Fraction ◽  
Nox Reduction ◽  
Combustion Process ◽  
Nox Emission ◽  
Moment Closure ◽  
Combustion Model ◽  
Industrial Furnace ◽  
Reduction Of Nox ◽  
Closure Method ◽  
Probability Density Function Pdf

The analysis of the combustion process and NOx emission in a gas-fired regenerative industrial furnace has been carried out numerically. The effect of the additive, methanol CH3OH, to the fuel on the NOx emission is studied. A moment closure method with the assumed β Probability Density Function (PDF) for the mixture fraction is used to model the turbulent non-premixed combustion process in the furnace. The combustion model is based on the assumption of instantaneous full chemical equilibrium. The P-1 model is chosen as the radiation model, and the Weighted-Sum-of-Gray-Gases Model is used to calculate the absorption coefficient. The numerical results showed that the use of CH3OH is effective in the reduction of NOx in a regenerative industrial furnace. The mechanism of NOx reduction by the use of CH3OH is also discussed.

scholarly journals Quantifying errors in surface ozone predictions associated with clouds over the CONUS: a WRF-Chem modeling study using satellite cloud retrievals

2018 ◽  
Vol 18 (10) ◽  
pp. 7509-7525 ◽  
Author(s):  
Young-Hee Ryu ◽  
Alma Hodzic ◽  
Jerome Barre ◽  
Gael Descombes ◽  
Patrick Minnis
Keyword(s):  
Urban Areas ◽  
Surface Ozone ◽  
Horizontal Resolution ◽  
Cumulus Parameterization ◽  
Weather Research And Forecasting ◽  
Photolysis Rates ◽  
Volatile Organic ◽  
Atmospheric Data ◽  
The Right ◽  
Surface O3

Abstract. Clouds play a key role in radiation and hence O3 photochemistry by modulating photolysis rates and light-dependent emissions of biogenic volatile organic compounds (BVOCs). It is not well known, however, how much error in O3 predictions can be directly attributed to error in cloud predictions. This study applies the Weather Research and Forecasting with Chemistry (WRF-Chem) model at 12 km horizontal resolution with the Morrison microphysics and Grell 3-D cumulus parameterization to quantify uncertainties in summertime surface O3 predictions associated with cloudiness over the contiguous United States (CONUS). All model simulations are driven by reanalysis of atmospheric data and reinitialized every 2 days. In sensitivity simulations, cloud fields used for photochemistry are corrected based on satellite cloud retrievals. The results show that WRF-Chem predicts about 55 % of clouds in the right locations and generally underpredicts cloud optical depths. These errors in cloud predictions can lead to up to 60 ppb of overestimation in hourly surface O3 concentrations on some days. The average difference in summertime surface O3 concentrations derived from the modeled clouds and satellite clouds ranges from 1 to 5 ppb for maximum daily 8 h average O3 (MDA8 O3) over the CONUS. This represents up to ∼ 40 % of the total MDA8 O3 bias under cloudy conditions in the tested model version. Surface O3 concentrations are sensitive to cloud errors mainly through the calculation of photolysis rates (for ∼ 80 %), and to a lesser extent to light-dependent BVOC emissions. The sensitivity of surface O3 concentrations to satellite-based cloud corrections is about 2 times larger in VOC-limited than NOx-limited regimes. Our results suggest that the benefits of accurate predictions of cloudiness would be significant in VOC-limited regions, which are typical of urban areas.

scholarly journals Response of atmospheric composition to COVID-19 lockdown measures during spring in the Paris region (France)

2021 ◽  
Vol 21 (22) ◽  
pp. 17167-17183
Author(s):  
Jean-Eudes Petit ◽  
Jean-Charles Dupont ◽  
Olivier Favez ◽  
Valérie Gros ◽  
Yunjiang Zhang ◽  
...  
Keyword(s):  
Air Quality ◽  
Urban Areas ◽  
Pollutant Emissions ◽  
Atmospheric Composition ◽  
Carbonaceous Aerosols ◽  
Low Carbon ◽  
Atmospheric Pollutant ◽  
Ambient Concentrations ◽  
The Impact ◽  
Mitigation Policies

Abstract. Since early 2020, the COVID-19 pandemic has led to lockdowns at national scales. These lockdowns resulted in large cuts of atmospheric pollutant emissions, notably related to the vehicular traffic source, especially during spring 2020. As a result, air quality changed in manners that are still currently under investigation. The robust quantitative assessment of the impact of lockdown measures on ambient concentrations is however hindered by weather variability. In order to circumvent this difficulty, an innovative methodology has been developed. The Analog Application for Air Quality (A3Q) method is based on the comparison of each day of lockdown to a group of analog days having similar meteorological conditions. The A3Q method has been successfully evaluated and applied to a comprehensive in situ dataset of primary and secondary pollutants obtained at the SIRTA observatory, a suburban background site of the megacity of Paris (France). The overall slight decrease of submicron particulate matter (PM1) concentrations (−14 %) compared to business-as-usual conditions conceals contrasting behaviors. Primary traffic tracers (NOx and traffic-related carbonaceous aerosols) dropped by 42 %–66 % during the lockdown period. Further, the A3Q method enabled us to characterize changes triggered by NOx decreases. Particulate nitrate and secondary organic aerosols (SOAs), two of the main springtime aerosol components in northwestern Europe, decreased by −45 % and −25 %, respectively. A NOx relationship emphasizes the interest of NOx mitigation policies at the regional (i.e., city) scale, although long-range pollution advection sporadically overcompensated for regional decreases. Variations of the oxidation state of SOA suggest discrepancies in SOA formation processes. At the same time, the expected ozone increase (+20 %) underlines the negative feedback of NO titration. These results provide a quasi-comprehensive observation-based insight for mitigation policies regarding air quality in future low-carbon urban areas.

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