Evaluating the sensitivity of radical chemistry and ozone formation to
ambient VOCs and NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; in Beijing

Whalley, Lisa K.; Slater, Eloise; Woodward-Massey, Robert; Ye, Chunxiang; Lee, James; Squires, Freya A.; Hopkins, James R.; Dunmore, Rachel E.; Shaw, Marvin; Hamilton, Jacqueline F.; Lewis, Alastair C.; Mehra, Archit; Worrall, Stephen D.; Bacak, Asan; Bannan, Thomas J.; Coe, Hugh; Ouyang, Bo; Jones, R. L.; Crilley, Leigh R.; Kramer, Louisa J.; Bloss, William J.; Vu, Tuan V.; Kotthaus, Simone; Grimmond, Sue; Sun, Yele; Xu, Weiqi; Yue, Siyao; Ren, Lujie; Acton, W. Joe F.; Hewitt, C. Nicholas; Wang, Xinming; Fu, Pingqing; Heard, Dwayne E.

doi:10.5194/acp-2020-785

Cited by 16 publications

(39 citation statements)

References 37 publications

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“…with the large overprediction of HO 2 in haze and non-haze events driving the overprediction of OH by a factor of 2.2 and 2.5. This highlights that the additional primary RO 2 source may be an RO 2 species that does not readily propagate to HO 2 ; this has also been discussed in Whalley et al (2020). To investigate whether the uptake of HO 2 onto the surface of aerosols could improve the agreement between measured and modelled HO 2 , the MCM-PRO2 model was modified to include the uptake of HO 2 with the uptake coefficient set equal to 0.2, as suggested by Jacob (2000), in model run MCM-PRO2-SA.…”

Section: Dependence Of Radicals Concentrations With No Xmentioning

confidence: 79%

“…The Leeds IPI was first implemented during the ICOZA campaign in Norfolk, UK, in the summer of 2015 and is described in further detail elsewhere (Woodward-Massey et al, 2020). During the APHH winter campaign the laser online (wavelength tuned to the OH transition) period lasted 300 s for both OHchem and OHwave data acquisition cycles.…”

Section: Inlet Pre-injectormentioning

confidence: 99%

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Elevated levels of OH observed in haze events during wintertime in central Beijing

et al. 2020

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Abstract. Wintertime in situ measurements of OH, HO2 and RO2 radicals and OH reactivity were made in central Beijing during November and December 2016. Exceptionally elevated NO was observed on occasions, up to ∼250 ppbv. The daily maximum mixing ratios for radical species varied significantly day-to-day over the ranges 1–8×106 cm−3 (OH), 0.2–1.5×108 cm−3 (HO2) and 0.3–2.5×108 cm−3 (RO2). Averaged over the full observation period, the mean daytime peak in radicals was 2.7×106, 0.39×108 and 0.88×108 cm−3 for OH, HO2 and total RO2, respectively. The main daytime source of new radicals via initiation processes (primary production) was the photolysis of HONO (∼83 %), and the dominant termination pathways were the reactions of OH with NO and NO2, particularly under polluted haze conditions. The Master Chemical Mechanism (MCM) v3.3.1 operating within a box model was used to simulate the concentrations of OH, HO2 and RO2. The model underpredicted OH, HO2 and RO2, especially when NO mixing ratios were high (above 6 ppbv). The observation-to-model ratio of OH, HO2 and RO2 increased from ∼1 (for all radicals) at 3 ppbv of NO to a factor of ∼3, ∼20 and ∼91 for OH, HO2 and RO2, respectively, at ∼200 ppbv of NO. The significant underprediction of radical concentrations by the MCM suggests a deficiency in the representation of gas-phase chemistry at high NOx. The OH concentrations were surprisingly similar (within 20 % during the day) in and outside of haze events, despite j(O1D) decreasing by 50 % during haze periods. These observations provide strong evidence that gas-phase oxidation by OH can continue to generate secondary pollutants even under high-pollution episodes, despite the reduction in photolysis rates within haze.

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Section: Dependence Of Radicals Concentrations With No Xmentioning

confidence: 79%

Section: Inlet Pre-injectormentioning

confidence: 99%

Elevated levels of OH observed in haze events during wintertime in central Beijing

et al. 2020

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“…However, in Beijing, the extreme suppression of NO concentrations in the afternoon drives the chemistry from a regime in which > 95 % of the RO 2 is reacting with NO during the morning to one in which less than 70 % is reacting with NO by the mid-afternoon. HO 2 concentrations were measured by FAGE during the campaign (Whalley et al, 2020). Concentrations peaked in the mid-afternoon (i.e.…”

Section: Box Modellingmentioning

confidence: 99%

Low-NO atmospheric oxidation pathways in a polluted megacity

et al. 2021

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Abstract. The impact of emissions of volatile organic compounds (VOCs) to the atmosphere on the production of secondary pollutants, such as ozone and secondary organic aerosol (SOA), is mediated by the concentration of nitric oxide (NO). Polluted urban atmospheres are typically considered to be “high-NO” environments, while remote regions such as rainforests, with minimal anthropogenic influences, are considered to be “low NO”. However, our observations from central Beijing show that this simplistic separation of regimes is flawed. Despite being in one of the largest megacities in the world, we observe formation of gas- and aerosol-phase oxidation products usually associated with low-NO “rainforest-like” atmospheric oxidation pathways during the afternoon, caused by extreme suppression of NO concentrations at this time. Box model calculations suggest that during the morning high-NO chemistry predominates (95 %) but in the afternoon low-NO chemistry plays a greater role (30 %). Current emissions inventories are applied in the GEOS-Chem model which shows that such models, when run at the regional scale, fail to accurately predict such an extreme diurnal cycle in the NO concentration. With increasing global emphasis on reducing air pollution, it is crucial for the modelling tools used to develop urban air quality policy to be able to accurately represent such extreme diurnal variations in NO to accurately predict the formation of pollutants such as SOA and ozone.

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“…Average traffic volume on artery roads peaked at ∼ 3100 vehicles h −1 (07:00 LT) with a minimum average flow of ∼ 250 vehicles h −1 (03:00 LT). In 2002, the dominant tree species in Beijing were Sophora japonica, Populus tomentosa and Juniperus chinensis (Yang et al, 2005). Large-scale tree planting occurred between 2012 and 2015, increasing forest cover by 10 %, with the main species planted being Pinus tabuli-formis, Sophora japonica, Fraxinus chinensis, Salix spp.…”

Section: Site Descriptionmentioning

confidence: 99%

Surface–atmosphere fluxes of volatile organic compounds in Beijing

et al. 2020

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Abstract. Mixing ratios of volatile organic compounds (VOCs) were recorded in two field campaigns in central Beijing as part of the Air Pollution and Human Health in a Chinese Megacity (APHH) project. These data were used to calculate, for the first time in Beijing, the surface–atmosphere fluxes of VOCs using eddy covariance, giving a top-down estimation of VOC emissions from a central area of the city. The results were then used to evaluate the accuracy of the Multi-resolution Emission Inventory for China (MEIC). The APHH winter and summer campaigns took place in November and December 2016 and May and June 2017, respectively. The largest VOC fluxes observed were of small oxygenated compounds such as methanol, ethanol + formic acid and acetaldehyde, with average emission rates of 8.31 ± 8.5, 3.97 ± 3.9 and 1.83 ± 2.0 nmol m−2 s−1, respectively, in the summer. A large flux of isoprene was observed in the summer, with an average emission rate of 5.31 ± 7.7 nmol m−2 s−1. While oxygenated VOCs made up 60 % of the molar VOC flux measured, when fluxes were scaled by ozone formation potential and peroxyacyl nitrate (PAN) formation potential the high reactivity of isoprene and monoterpenes meant that these species represented 30 % and 28 % of the flux contribution to ozone and PAN formation potential, respectively. Comparison of measured fluxes with the emission inventory showed that the inventory failed to capture the magnitude of VOC emissions at the local scale.

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Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO<sub>x</sub> in Beijing

Cited by 16 publications

References 37 publications

Elevated levels of OH observed in haze events during wintertime in central Beijing

Elevated levels of OH observed in haze events during wintertime in central Beijing

Low-NO atmospheric oxidation pathways in a polluted megacity

Surface–atmosphere fluxes of volatile organic compounds in Beijing

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Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO&lt;sub&gt;x&lt;/sub&gt; in Beijing

Cited by 16 publications

References 37 publications

Elevated levels of OH observed in haze events during wintertime in central Beijing

Elevated levels of OH observed in haze events during wintertime in central Beijing

Low-NO atmospheric oxidation pathways in a polluted megacity

Surface–atmosphere fluxes of volatile organic compounds in Beijing

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Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO<sub>x</sub> in Beijing