Measurements of OH, HO2, complex RO2 (alkene- and aromatic-related RO2) and total RO2 radicals taken during the integrated Study of AIR Pollution PROcesses in Beijing (AIRPRO) campaign in central ...Beijing in the summer of 2017, alongside observations of OH reactivity, are presented. The concentrations of radicals were elevated, with OH reaching up to 2.8×107moleculecm-3, HO2 peaking at 1×109moleculecm-3 and the total RO2 concentration reaching 5.5×109moleculecm-3. OH reactivity (k(OH)) peaked at 89 s-1 during the night, with a minimum during the afternoon of ≈22s-1 on average. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbvh-1) under the very low NO conditions (<0.5ppbv) experienced in the afternoons, demonstrating a missing OH source consistent with previous studies under high volatile organic compound (VOC) emissions and low NO loadings. Under the highest NO mixing ratios (104 ppbv), the HO2 production rate exceeded the rate of destruction by ≈50ppbvh-1, whilst the rate of destruction of total RO2 exceeded the production by the same rate, indicating that the net propagation rate of RO2 to HO2 may be substantially slower than assumed. If just 10 % of the RO2 radicals propagate to HO2 upon reaction with NO, the HO2 and RO2 budgets could be closed at high NO, but at low NO this lower RO2 to HO2 propagation rate revealed a missing RO2 sink that was similar in magnitude to the missing OH source. A detailed box model that incorporated the latest Master Chemical Mechanism (MCM3.3.1) reproduced the observed OH concentrations well but over-predicted the observed HO2 under low concentrations of NO (<1ppbv) and under-predicted RO2 (both the complex RO2 fraction and other RO2 types which we classify as simple RO2) most significantly at the highest NO concentrations. The model also under-predicted the observed k(OH) consistently by ≈10s-1 across all NOx levels, highlighting that the good agreement for OH was fortuitous due to a cancellation of missing OH source and sink terms in its budget. Including heterogeneous loss of HO2 to aerosol surfaces did reduce the modelled HO2 concentrations in line with the observations but only at NO mixing ratios <0.3ppbv. The inclusion of Cl atoms, formed from the photolysis of nitryl chloride, enhanced the modelled RO2 concentration on several mornings when the Cl atom concentration was calculated to exceed 1×104atomscm-3 and could reconcile the modelled and measured RO2 concentrations at these times. However, on other mornings, when the Cl atom concentration was lower, large under-predictions in total RO2 remained. Furthermore, the inclusion of Cl atom chemistry did not enhance the modelled RO2 beyond the first few hours after sunrise and so was unable to resolve the modelled under-prediction in RO2 observed at other times of the day. Model scenarios, in which missing VOC reactivity was included as an additional reaction that converted OH to RO2, highlighted that the modelled OH, HO2 and RO2 concentrations were sensitive to the choice of RO2 product. The level of modelled to measured agreement for HO2 and RO2 (both complex and simple) could be improved if the missing OH reactivity formed a larger RO2 species that was able to undergo reaction with NO, followed by isomerisation reactions reforming other RO2 species, before eventually generating HO2. In this work an α-pinene-derived RO2 species was used as an example. In this simulation, consistent with the experimental budget analysis, the model underestimated the observed OH, indicating a missing OH source. The model uncertainty, with regards to the types of RO2 species present and the radicals they form upon reaction with NO (HO2 directly or another RO2 species), leads to over an order of magnitude less O3 production calculated from the predicted peroxy radicals than calculated from the observed peroxy radicals at the highest NO concentrations. This demonstrates the rate at which the larger RO2 species propagate to HO2, to another RO2 or indeed to OH needs to be understood to accurately simulate the rate of ozone production in environments such as Beijing, where large multifunctional VOCs are likely present.
Ambient particulate matter (PM) can contain a mix of
different toxic species derived from a wide variety of sources. This study
quantifies the diurnal variation and nocturnal abundance of ...16 polycyclic
aromatic hydrocarbons (PAHs), 10 oxygenated PAHs (OPAHs) and 9 nitrated PAHs
(NPAHs) in ambient PM in central Beijing during winter. Target compounds
were identified and quantified using gas chromatography–time-of-flight
mass spectrometry (GC-Q-ToF-MS). The total concentration of PAHs varied
between 18 and 297 ng m−3 over 3 h daytime filter samples and from 23
to 165 ng m−3 in 15 h night-time samples. The total concentrations of
PAHs over 24 h varied between 37 and 180 ng m−3 (mean: 97±43 ng m−3).
The total daytime concentrations during high particulate loading
conditions for PAHs, OPAHs and NPAHs were 224, 54 and 2.3 ng m−3,
respectively. The most abundant PAHs were fluoranthene (33 ng m−3),
chrysene (27 ng m−3), pyrene (27 ng m−3), benzoapyrene (27 ng m−3), benzobfluoranthene (25 ng m−3), benzoaanthracene (20 ng m−3) and phenanthrene (18 ng m−3). The most abundant OPAHs were
9,10-anthraquinone (18 ng m−3), 1,8-naphthalic anhydride (14 ng m−3) and 9-fluorenone (12 ng m−3), and the three most abundant
NPAHs were 9-nitroanthracene (0.84 ng m−3), 3-nitrofluoranthene (0.78 ng m−3) and 3-nitrodibenzofuran (0.45 ng m−3). ∑PAHs and
∑OPAHs showed a strong positive correlation with the gas-phase
abundance of NO, CO, SO2 and HONO, indicating that PAHs and OPAHs can
be associated with both local and regional emissions. Diagnostic ratios
suggested emissions from traffic road and coal combustion were the
predominant sources of PAHs in Beijing and also revealed the main source
of NPAHs to be secondary photochemical formation rather than primary
emissions. PM2.5 and NPAHs showed a strong correlation with gas-phase
HONO. 9-Nitroanthracene appeared to undergo a photodegradation during the
daytime and showed a strong positive correlation with ambient HONO
(R=0.90, P < 0.001). The lifetime excess lung cancer risk for those
species that have available toxicological data (16 PAHs, 1 OPAH and 6 NPAHs)
was calculated to be in the range 10−5 to 10−3 (risk per million
people ranges from 26 to 2053 cases per year).
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.
The Indian megacity of Delhi suffers from some of the
poorest air quality in the world. While ambient NO2 and particulate
matter (PM) concentrations have received considerable attention in the city,
...high ground-level ozone (O3) concentrations are an often overlooked
component of pollution. O3 can lead to significant ecosystem damage and
agricultural crop losses, and adversely affect human health. During October 2018,
concentrations of speciated non-methane hydrocarbon volatile organic
compounds (C2–C13), oxygenated volatile organic compounds
(o-VOCs), NO, NO2, HONO, CO, SO2, O3, and photolysis rates,
were continuously measured at an urban site in Old Delhi. These observations
were used to constrain a detailed chemical box model utilising the Master
Chemical Mechanism v3.3.1. VOCs and NOx (NO + NO2) were varied
in the model to test their impact on local O3 production rates,
P(O3), which revealed a VOC-limited chemical regime. When only NOx
concentrations were reduced, a significant increase in P(O3) was
observed; thus, VOC co-reduction approaches must also be considered in
pollution abatement strategies. Of the VOCs examined in this work, mean
morning P(O3) rates were most sensitive to monoaromatic compounds,
followed by monoterpenes and alkenes, where halving their concentrations in
the model led to a 15.6 %, 13.1 %, and 12.9 % reduction in
P(O3), respectively. P(O3) was not sensitive to direct changes in
aerosol surface area but was very sensitive to changes in photolysis rates,
which may be influenced by future changes in PM concentrations. VOC and
NOx concentrations were divided into emission source sectors, as
described by the Emissions Database for Global Atmospheric Research (EDGAR) v5.0 Global Air Pollutant Emissions and EDGAR
v4.3.2_VOC_spec inventories, allowing for the
impact of individual emission sources on P(O3) to be investigated.
Reducing road transport emissions only, a common strategy in air pollution
abatement strategies worldwide, was found to increase P(O3), even when
the source was removed in its entirety. Effective reduction in P(O3)
was achieved by reducing road transport along with emissions from combustion
for manufacturing and process emissions. Modelled P(O3) reduced by
∼ 20 ppb h−1 when these combined sources were halved. This study
highlights the importance of reducing VOCs in parallel with NOx and PM
in future pollution abatement strategies in Delhi.
Isoprene-derived secondary organic aerosol (iSOA) is a significant
contributor to organic carbon (OC) in some forested regions, such as
tropical rainforests and the Southeastern US. However, its ...contribution to
organic aerosol in urban areas that have high levels of anthropogenic
pollutants is poorly understood. In this study, we examined the formation of
anthropogenically influenced iSOA during summer in Beijing, China. Local
isoprene emissions and high levels of anthropogenic pollutants, in
particular NOx and particulate SO42-, led to the formation of
iSOA under both high- and low-NO oxidation conditions, with significant
heterogeneous transformations of isoprene-derived oxidation products to
particulate organosulfates (OSs) and nitrooxy-organosulfates (NOSs).
Ultra-high-performance liquid chromatography coupled to high-resolution mass
spectrometry was combined with a rapid automated data processing technique
to quantify 31 proposed iSOA tracers in offline PM2.5 filter
extracts. The co-elution of the inorganic ions in the extracts caused matrix
effects that impacted two authentic standards differently. The average
concentration of iSOA OSs and NOSs was 82.5 ng m−3, which was around 3 times
higher than the observed concentrations of their oxygenated precursors
(2-methyltetrols and 2-methylglyceric acid). OS formation was dependant on
both photochemistry and the sulfate available for reactive uptake, as shown by a
strong correlation with the product of ozone (O3) and particulate
sulfate (SO42-). A greater proportion of high-NO OS products were
observed in Beijing compared with previous studies in less polluted
environments. The iSOA-derived OSs and NOSs represented 0.62 %
of the oxidized organic aerosol measured by aerosol mass spectrometry on average, but
this increased to ∼3 % on certain days. These results
indicate for the first time that iSOA formation in urban Beijing is strongly
controlled by anthropogenic emissions and results in extensive conversion to
OS products from heterogenous reactions.
We present high-resolution (5 km × 5 km) atmospheric chemical transport model (ACTM) simulations of the impact of newly estimated traffic-related emissions on secondary organic aerosol (SOA) ...formation over the UK for 2012. Our simulations include additional diesel-related intermediate-volatility organic compound (IVOC) emissions derived directly from comprehensive field measurements at an urban background site in London during the 2012 Clean Air for London (ClearfLo) campaign. Our IVOC emissions are added proportionally to VOC emissions, as opposed to proportionally to primary organic aerosol (POA) as has been done by previous ACTM studies seeking to simulate the effects of these missing emissions. Modelled concentrations are evaluated against hourly and daily measurements of organic aerosol (OA) components derived from aerosol mass spectrometer (AMS) measurements also made during the ClearfLo campaign at three sites in the London area. According to the model simulations, diesel-related IVOCs can explain on average ∼ 30 % of the annual SOA in and around London. Furthermore, the 90th percentile of modelled daily SOA concentrations for the whole year is 3.8 µg m−3, constituting a notable addition to total particulate matter. More measurements of these precursors (currently not included in official emissions inventories) is recommended. During the period of concurrent measurements, SOA concentrations at the Detling rural background location east of London were greater than at the central London location. The model shows that this was caused by an intense pollution plume with a strong gradient of imported SOA passing over the rural location. This demonstrates the value of modelling for supporting the interpretation of measurements taken at different sites or for short durations.
Rural observations of air quality and meteorological parameters (NOx, O3, NMHCs, SO2, PM) were made over a 2.5-year period (2016–2018) before, during and after preparations for hydraulic fracturing ...(fracking) at a shale gas exploration site near Kirby Misperton, North Yorkshire, England. As one of the first sites to apply for permits to carry out hydraulic fracturing, it has been subject to extensive regulatory and public scrutiny, as well as the focus for a major programme of long-term environmental monitoring. A baseline period of air quality monitoring (starting 2016) established the annual climatology of atmospheric composition against which a 20-week period of intensive activity on the site in preparation for hydraulic fracturing could be compared. During this ‘pre-operational phase’ of work in late 2017, the most significant effect was an increase in ambient NO (3-fold) and NOx (2-fold), arising from a combination of increased vehicle activity and operation of equipment on site. Although ambient NOx increased, air quality limit values for NO2 were not exceeded, even close to the well-site. Local ozone concentrations during the pre-operational period were slightly lower than the baseline phase due to titration with primary emitted NO. The activity on site did not lead to significant changes in airborne particulate matter or non-methane hydrocarbons. Hydraulic fracturing of the well did not subsequently take place and the on-site equipment was decommissioned and removed. Air quality parameters then returned to the original (baseline) climatological conditions. This work highlights the need to characterise the full annual climatology of air quality parameters against which short-term local activity changes can be compared. Based on this study, changes to ambient NOx appear to be the most significant air quality ahead of hydraulic fracturing. However, in rural locations, concentrations at individual sites are expected to be below ambient air quality limit thresholds.
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•First observational assessment of incremental air quality impacts of operations at a shale gas site in the UK.•Observations show due to baseline variability one annual cycle of measurements is needed to establish a local climatology.•During “pre-operational phase” NO increased 3-fold from combination of increased vehicle activity and site operations.•Although NO2 also increased, air quality limit values for NO2 were not exceeded
Twenty-nine different fuel types used in residential dwellings in northern India were collected from across Delhi (76 samples in total). Emission factors of a wide range of non-methane volatile ...organic compounds (NMVOCs) (192 compounds in total) were measured during controlled burning experiments using dual-channel gas chromatography with flame ionisation detection (DC-GC-FID), two-dimensional gas chromatography (GC x GC-FID), proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and solid-phase extraction two-dimensional gas chromatography with time-of-flight mass spectrometry (SPE-GC x GC-ToF-MS). On average, 94 % speciation of total measured NMVOC emissions was achieved across all fuel types. The largest contributors to emissions from most fuel types were small non-aromatic oxygenated species, phenolics and furanics. The emission factors (in g kg.sup.-1) for total gas-phase NMVOCs were fuelwood (18.7, 4.3-96.7), cow dung cake (62.0, 35.3-83.0), crop residue (37.9, 8.9-73.8), charcoal (5.4, 2.4-7.9), sawdust (72.4, 28.6-115.5), municipal solid waste (87.3, 56.6-119.1) and liquefied petroleum gas (5.7, 1.9-9.8).
The impact of heterogeneous uptake of HO2 on aerosol surfaces on radical concentrations and the O3 production regime in Beijing in summertime was investigated. The uptake coefficient of HO2 onto ...aerosol surfaces, γHO2, was calculated for the AIRPRO campaign in Beijing, in summer 2017, as a function of measured aerosol soluble copper concentration, Cu2+eff, aerosol liquid water content, ALWC, and particulate matter concentration, PM. An average γHO2 across the entire campaign of 0.070±0.035 was calculated, with values ranging from 0.002 to 0.15, and found to be significantly lower than the value of γHO2=0.2, commonly used in modelling studies. Using the calculated γHO2 values for the summer AIRPRO campaign, OH, HO2 and RO2 radical concentrations were modelled using a box model incorporating the Master Chemical Mechanism (v3.3.1), with and without the addition of γHO2, and compared to the measured radical concentrations. The rate of destruction analysis showed the dominant HO2 loss pathway to be HO2 + NO for all NO concentrations across the summer Beijing campaign, with HO2 uptake contributing <0.3 % to the total loss of HO2 on average. This result for Beijing summertime would suggest that under most conditions encountered, HO2 uptake onto aerosol surfaces is not important to consider when investigating increasing O3 production with decreasing PM across the North China Plain. At low NO, however, i.e. <0.1 ppb, which was often encountered in the afternoons, up to 29 % of modelled HO2 loss was due to HO2 uptake on aerosols when calculated γHO2 was included, even with the much lowerγHO2 values compared to γHO2= 0.2, a result which agrees with the aerosol-inhibited O3 regime recently proposed by Ivatt et al. (2022). As such it can be concluded that in cleaner environments, away from polluted urban centres where HO2 loss chemistry is not dominated by NO but where aerosol surface area is high still, changes in PM concentration and hence aerosol surface area could still have a significant effect on both overall HO2 concentration and the O3 production regime.Using modelled radical concentrations, the absolute O3 sensitivity to NOx and volatile organic compounds (VOCs) showed that, on average across the summer AIRPRO campaign, the O3 production regime remained VOC-limited, with the exception of a few days in the afternoon when the NO mixing ratio dropped low enough for the O3 regime to shift towards being NOx-limited. The O3 sensitivity to VOCs, the dominant regime during the summer AIRPRO campaign, was observed to decrease and shift towards a NOx-sensitive regime both when NO mixing ratio decreased and with the addition of aerosol uptake. This suggests that if NOx continues to decrease in the future, ozone reduction policies focussing solely on NOx reductions may not be as efficient as expected if PM and, hence, HO2 uptake to aerosol surfaces continue to decrease. The addition of aerosol uptake into the model, for both the γHO2 calculated from measured data and when using a fixed value of γHO2=0.2, did not have a significant effect on the overall O3 production regime across the campaign. While not important for this campaign, aerosol uptake could be important for areas of lower NO concentration that are already in a NOx-sensitive regime.
The abundance of volatile organic compounds (VOCs) found in homes depends on many factors such as emissions, ventilation and the oxidative environment and these are evolving over time, reflecting ...changes in chemical use, behaviour and building design/materials. The concentrations of VOCs in 25 UK homes of varying ages, design and occupancy were quantified using continuous indoor air sampling over five days. Air was collected through low flow (1 mL min
) constant flow restrictors into evacuated 6 L internally silica-treated canisters until the canisters reached atmospheric pressure. This was followed by thermal desorption-gas chromatography and high mass accuracy time-of-flight mass spectrometry (TD-GC-TOF/MS). A fully quantitative analysis was performed on the eight most abundant hydrocarbon-based VOCs found. Despite differences in building characteristics and occupant numbers 94% of the homes had d-limonene or α-pinene as the most abundant VOCs. The variability seen across the 25 homes in concentrations of monoterpenes indoors was considerably greater than that of species such as isoprene, benzene, toluene and xylenes. The variance in VOCs indoors appeared to be strongly influenced by occupant activities such as cleaning with 5-day average concentrations of d-limonene ranging from 18 μg m
to over 1400 μg m
, a peak domestic value that is possibly the highest yet reported in the literature.
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