Photochemical impacts of haze pollution in an urban environment

Hollaway, Michael; Wild, Oliver; Yang, Ting; Sun, Yele; Xu, Weiqi; Xie, Conghui; Whalley, Lisa K.; Slater, Eloise; Heard, Dwayne E.; Liu, Dantong

doi:10.5194/acp-19-9699-2019

Cited by 35 publications

(23 citation statements)

References 57 publications

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“…S3 –f) in VOC-limited chemical regime of Delhi 27 – 29 . A simultaneous reduction in PM 2.5 would have also contributed to this increase in O 3 attributed to the effects of aerosols on photolysis 7 , 29 , 30 .…”

Section: Resultsmentioning

confidence: 99%

PM2.5 diminution and haze events over Delhi during the COVID-19 lockdown period: an interplay between the baseline pollution and meteorology

Dhaka

Chetna

Kumar

et al. 2020

Sci Rep

105

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Delhi, a tropical indian megacity, experiences one of the most severe air pollution in the world, linked with diverse anthropogenic and biomass burning emissions. First phase of COVID-19 lockdown in India, implemented during 25 March to 14 April 2020 resulted in a dramatic near-zeroing of various activities (e.g. traffic, industries, constructions), except the "essential services". Here, we analysed variations in the fine particulate matter (PM 2.5) over the Delhi-National Capital Region. Measurements revealed large reductions (by 40-70%) in PM 2.5 during the first week of lockdown (25-31 March 2020) as compared to the pre-lockdown conditions. However, O 3 pollution remained high during the lockdown due to non-linear chemistry and dynamics under low aerosol loading. Notably, events of enhanced pM 2.5 levels (300-400 µg m −3) were observed during night and early morning hours in the first week of April after air temperatures fell close to the dew-point (~ 15-17 °C). A haze formation mechanism is suggested through uplifting of fine particles, which is reinforced by condensation of moisture following the sunrise. The study highlights a highly complex interplay between the baseline pollution and meteorology leading to counter intuitive enhancements in pollution, besides an overall improvement in air quality during the COVID-19 lockdown in this part of the world. The pandemic due to spread of novel Corona virus, commonly known as the COVID-19, has led to partial or complete lockdown in several countries around the world. The spread of deadly virus has caused deaths estimated to more than two hundred thousand people over a period of December 2019-April 2020. However, air pollutants and COVID-19 are linked to have played a major role in huge number of deaths 1,2. In order to contain its impact in India, the first phase of complete lockdown imposed from 25 March to 14 April 2020, which was further extended till 03 May 2020. As a result, the transport, construction works, industries and other commercial activities, which could have injected pollutants or produce dust, are stopped and remained at its minimal level. Unprecedented reductions in anthropogenic activities yielded to very low values of emissions resulting in significantly improved air quality over the Delhi-National Capital Region (NCR) [up to 50% reduction in fine particle

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Section: Resultsmentioning

confidence: 99%

PM2.5 diminution and haze events over Delhi during the COVID-19 lockdown period: an interplay between the baseline pollution and meteorology

Dhaka

Chetna

Kumar

et al. 2020

Sci Rep

105

View full text Add to dashboard Cite

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“…From this basic theoretical perspective, the model bias in wintertime ozone should at least partly explain the underestimate in [NO 2 ] in our simulations. The actual NO x -O 3 relationship may deviate from Leighton's prediction because of the complicated interaction between aerosols and radiation, which can affect the photolysis of NO 2 and O 3 (Hollaway et al, 2019;. As explained in Section 3.2, low [O 3 ] can also limit nitrate production via N 2 O 5 uptake in NO x -rich air.…”

Section: Possible Causes Of Modeled Underestimate In Wintertime [O X ] In the Ncp And Their Potential Influence On No Y Chemistrymentioning

confidence: 99%

Heterogeneous Nitrate Production Mechanisms in Intense Haze Events in the North China Plain

Chan

Evans

et al. 2021

JGR Atmospheres

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Studies of wintertime air quality in the North China Plain (NCP) show that particulate‐nitrate pollution persists despite rapid reduction in NOx emissions. This intriguing NOx‐nitrate relationship may originate from non‐linear nitrate‐formation chemistry, but it is unclear which feedback mechanisms dominate in NCP. In this study, we re‐interpret the wintertime observations of 17O excess of nitrate (∆17O(NO3−)) in Beijing using the GEOS‐Chem (GC) chemical transport model to estimate the importance of various nitrate‐production pathways and how their contributions change with the intensity of haze events. We also analyze the relationships between other metrics of NOy chemistry and [PM2.5] in observations and model simulations. We find that the model on average has a negative bias of −0.9‰ and −36% for ∆17O(NO3−) and [Ox,major] (≡ [O3] + [NO2] + [p‐NO3−]), respectively, while overestimating the nitrogen oxidation ratio ([NO3−]/([NO3−] + [NO2])) by +0.12 in intense haze. The discrepancies become larger in more intense haze. We attribute the model biases to an overestimate of NO2‐uptake on aerosols and an underestimate in wintertime O3 concentrations. Our findings highlight a need to address uncertainties related to heterogeneous chemistry of NO2 in air‐quality models. The combined assessment of observations and model results suggest that N2O5 uptake in aerosols and clouds is the dominant nitrate‐production pathway in wintertime Beijing, but its rate is limited by ozone under high‐NOx‐high‐PM2.5 conditions. Nitrate production rates may continue to increase as long as [O3] increases despite reduction in [NOx], creating a negative feedback that reduces the effectiveness of air pollution mitigation.

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“…In addition, reduced aerosol loadings during the prolonged shutdown could also lead to ozone enhancements through increased photolysis rates (e.g. Hollaway et al, 2019 ) and diminished uptake of hydroperoxyl radicals (HO 2 ) that remove NO from the atmosphere ( Li et al, 2019 ).…”

Section: Regional Analysis For Central and Southwestern Europementioning

confidence: 99%

Early spring near-surface ozone in Europe during the COVID-19 shutdown: Meteorological effects outweigh emission changes

Ordóñez

Garrido-Perez

García‐Herrera

2020

Science of The Total Environment

116

105

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This paper analyses the impact of the control measures during the COVID-19 lockdown in Europe (15 March–30 April 2020) on 1-h daily maximum nitrogen dioxide (NO 2 ) and maximum daily 8-h running average ozone (MDA8 O 3 ) observations obtained from the European Environment Agency's air quality database (AirBase). Daily maximum NO 2 decreased consistently over the whole continent, with relative reductions ranging from 5% to 55% with respect to the same period in 2015–2019 for 80% of the sites considered (10th – 90th percentiles). However, MDA8 O 3 concentrations showed a different pattern, decreasing over Iberia and increasing elsewhere. In particular, a large region from northwestern to central Europe experienced increases of 10–22% at urban background stations, reaching typical values of the summer season. The analysis of the expected NO 2 and O 3 concentrations in the absence of the lockdown, using generalised additive models fed by reanalysis meteorological data, shows that the low NO 2 concentrations were mostly attributed to the emission reductions while O 3 anomalies were dominated by the meteorology. The relevance of each meteorological variable depends on the location. The positive O 3 anomalies in northwestern and central Europe were mostly associated with elevated temperatures, low specific humidity and enhanced solar radiation. This pattern could be an analogue to study the limits of pollution control policies under climate change scenarios. On the other hand, the O 3 reduction in Iberia is mostly attributable to the low solar radiation and high specific humidity, although the reduced zonal wind also played a role in the proximity of the Iberian Mediterranean coast.

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Photochemical impacts of haze pollution in an urban environment

Cited by 35 publications

References 57 publications

PM2.5 diminution and haze events over Delhi during the COVID-19 lockdown period: an interplay between the baseline pollution and meteorology

PM2.5 diminution and haze events over Delhi during the COVID-19 lockdown period: an interplay between the baseline pollution and meteorology

Heterogeneous Nitrate Production Mechanisms in Intense Haze Events in the North China Plain

Early spring near-surface ozone in Europe during the COVID-19 shutdown: Meteorological effects outweigh emission changes

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