Do Absorbing Aerosols or Scattering Aerosols Dominate the Impact of Aerosols on Ozone via Influencing Photolysis Rates?

Abstract. The impact of Mexico City (MCMA) emissions is examined by studying its effects on air quality, photochemistry, and on ozone production regimes by combining model products and aircraft observations from the MILAGRO experiment during March 2006. The modeled influence of MCMA emissions to enhancements in surface level NOx, CO, and O3 concentrations (10–30% increase) are confined to distances <200 km, near surface. However, the extent of the influence is significantly larger at higher altitudes. Broader MCMA impacts (some 900 km Northeast of the city) are shown for specific outflow conditions in which enhanced ozone, NOy, and MTBE mixing ratios over the Gulf of Mexico are linked to MCMA by source tagged tracers and sensitivity runs. This study shows that the "footprint" of MCMA on average is fairly local, with exception to reactive nitrogen, which can be transported long range in the form of PAN, acting as a reservoir and source of NOx with important regional ozone formation implications. The simulated effect of MCMA emissions of anthropogenic aerosol on photochemistry showed a maximum regional decrease of 40% in J[NO2→NO+O], and resulting in the reduction of ozone production by 5–10%. Observed ozone production efficiencies are evaluated as a function of distance from MCMA, and by modeled influence from MCMA. These tend to be much lower closer to MCMA, or in those points where modeled contribution from MCMA is large. This research shows that MCMA emissions do effect on regional air quality and photochemistry, both contributing large amounts of ozone and its precursors, but with caveat that aerosol concentrations hinder formation of ozone to its potential due to its reduction in photolysis rates.

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Absorption coefficient of urban aerosol in Nanjing, west Yangtze River Delta, China

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-13633-2015 ◽

2015 ◽

Vol 15 (23) ◽

pp. 13633-13646 ◽

Cited By ~ 15

Author(s):

B. L. Zhuang ◽

T. J. Wang ◽

J. Liu ◽

Y. Ma ◽

C. Q. Yin ◽

...

Keyword(s):

Absorption Coefficient ◽

Urban Area ◽

Yangtze River ◽

Temporal Variations ◽

Yangtze River Delta ◽

River Delta ◽

Near Surface ◽

Absorbing Aerosols ◽

The Impact ◽

532 Nm

Abstract. Absorbing aerosols can significantly modulate short-wave solar radiation in the atmosphere, affecting regional and global climate. The aerosol absorption coefficient (AAC) is an indicator that assesses the impact of absorbing aerosols on radiative forcing. In this study, the near-surface AAC and absorption Ångström exponent (AAE) in the urban area of Nanjing, China, are characterized on the basis of measurements in 2012 and 2013 using the seven-channel Aethalometer (model AE-31, Magee Scientific, USA). The AAC is estimated with direct and indirect corrections, which result in consistent temporal variations and magnitudes of AAC at 532 nm. The mean AAC at 532 nm is about 43.23 ± 28.13 M m−1 in the urban area of Nanjing, which is much lower than that in Pearl River Delta and the same as in rural areas (Lin'an) in Yangtze River Delta. The AAC in the urban area of Nanjing shows strong seasonality (diurnal variations); it is high in cold seasons (at rush hour) and low in summer (in the afternoon). It also shows synoptic and quasi-2-week cycles in response to weather systems. Its frequency distribution follows a typical log-normal pattern. The 532 nm AAC ranging from 15 to 65 M m−1 dominates, accounting for more than 72 % of the total data samples in the entire study period. Frequent high pollution episodes, such as those observed in June 2012 and in winter 2013, greatly enhanced AAC and altered its temporal variations and frequency distributions. These episodes are mostly due to local emissions and regional pollution. Air masses flowing from northern China to Nanjing can sometimes be highly polluted and lead to high AAC at the site. AAE at 660/470 nm from the Schmid correction (Schmid et al., 2006) is about 1.56, which might be more reasonable than from the Weingartner correction (Weingartner et al., 2003). Low AAEs mainly occur in summer, likely due to high relative humidity (RH) in the season. AAC increases with increasing AAE at a fixed aerosol loading. The RH–AAC relationship is more complex. Overall, AAC peaks at RH values of around 40 % (1.3 < AAE < 1.6), 65 % (AAE < 1.3 and AAE > 1.6), and 80 % (1.3 < AAE < 1.6).

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Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

10.5194/acp-2017-12 ◽

2017 ◽

Author(s):

Ben Newsome ◽

Mat Evans

Keyword(s):

Rate Constant ◽

Atmospheric Chemistry ◽

Rate Constants ◽

Tropospheric Ozone ◽

Radiative Forcing ◽

Transport Model ◽

Surface Ozone ◽

Photolysis Rates ◽

The Impact ◽

Chemical Rate

Abstract. Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global use these rate constants. Expert panels synthesise laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the JPL and IUPAC evaluations we assess 50 mainly inorganic rate constants and 10 photolysis rates, through simulations where we increase the rate of the reactions to the 1σ upper value recommended by the expert panels. We assess the impact on 4 standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH M → HNO3, OH + CH4 → CH3O2 + H2O and O3 + NO → NO2 + O2 are the three largest source of uncertainty in these metrics. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions, gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 11, 12, 17 and 17 % respectively. These are larger than the spread between models in recent model inter-comparisons. Remote regions such as the tropics, poles, and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered when model results disagree with measurement. Calculations for the pre-industrial allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 Wm−2. This uncertainty (15 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model-model inter-comparison studies where the rate constants used in the models are all identical or very similar. Thus the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

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Modeling of photolysis rates over Europe: impact on chemical gaseous species and aerosols

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-1711-2011 ◽

2011 ◽

Vol 11 (4) ◽

pp. 1711-1727 ◽

Cited By ~ 28

Author(s):

E. Real ◽

K. Sartelet

Keyword(s):

Air Quality ◽

Transport Model ◽

Quantum Yields ◽

Strong Impact ◽

Peak Reduction ◽

Gaseous Species ◽

Clear Sky ◽

Photolysis Rate ◽

Photolysis Rates ◽

The Impact

Abstract. This paper evaluates the impact of photolysis rate calculation on simulated European air composition and air quality. In particular, the impact of the cloud parametrisation and the impact of aerosols on photolysis rates are analysed. Photolysis rates are simulated using the Fast-JX photolysis scheme and gas and aerosol concentrations over Europe are simulated with the regional chemistry-transport model Polair3D of the Polyphemus platform. The photolysis scheme is first used to update the clear-sky tabulation of photolysis rates used in the previous Polair3D version. Important differences in photolysis rates are simulated, mainly due to updated cross-sections and quantum yields in the Fast-JX scheme. In the previous Polair3D version, clouds were taken into account by multiplying the clear-sky photolysis rates by a correction factor. In the new version, clouds are taken into account more accurately by simulating them directly in the photolysis scheme. Differences in photolysis rates inside clouds can be large but outside clouds, and especially at the ground, differences are small. To take into account the impact of aerosols on photolysis rates, Polair3D and Fast-JX are coupled. Photolysis rates are updated every hour. Large impact on photolysis rates is observed at the ground, decreasing with altitude. The aerosol specie that impact the most photolysis rates is dust especially in south Europe. Strong impact is also observed over anthropogenic emission regions (Paris, The Po and the Ruhr Valley) where mainly nitrate and sulphate reduce the incoming radiation. Differences in photolysis rates lead to changes in gas concentrations, with the largest impact simulated on OH and NO concentrations. At the ground, monthly mean concentrations of both species are reduced over Europe by around 10 to 14% and their tropospheric burden by around 10%. The decrease in OH leads to an increase of the life-time of several species such as VOC. NO2 concentrations are not strongly impacted and O3 concentrations are mostly reduced at the ground (−3%). O3 peaks are systematically decreased because of the NO2 photolysis rate coefficient decrease. Not only gas are impacted but also secondary aerosols, due to changes in gas precursors concentrations. However changes in aerosol species concentrations often compensate each other resulting in a low impact on PM10 and PM2.5 concentrations (lower than 2%). The changes in gas concentrations at the ground induced by the modification of photolysis rates (by aerosols and clouds) are compared to changes induced by 29 different model parametrisations in Roustan et al. (2010). Among the 31 model parametrisations, "including aerosols on photolysis rates calculation" has the strongest impact on OH concentrations and on O3 bias in July. In terms of air quality, ground concentrations (NO2, O3, PM10) are compared with measurements. Changes arising from cloud parametrisation are small. Simulation performances are often slightly better when including aerosol in photolysis rates calculation. The systematic O3 peak reduction leads to large differences in the exceedances of the European O3 standard as calculated by the model, in better agreement with measurements. The number of exceedances of the information and the alert threshold is divided by 2 when the aerosol impact on photochemistry is simulated. This shows the importance of taking into account aerosols impact on photolysis rates in air quality studies.

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Multiyear Measurements of the Aerosol Absorption Coefficient Near the Surface in a Small-Sized Urban Area in Portugal

Advances in Meteorology ◽

10.1155/2014/830349 ◽

2014 ◽

Vol 2014 ◽

pp. 1-8 ◽

Cited By ~ 2

Author(s):

Sérgio Nepomuceno Pereira ◽

Frank Wagner ◽

Ana Maria Silva

Keyword(s):

Absorption Coefficient ◽

Mixing Layer ◽

Ground Level ◽

Average Increase ◽

Decay Function ◽

Strong Negative Correlation ◽

Aerosol Absorption ◽

Long Time ◽

Absorbing Aerosols ◽

The Impact

Measurements of the aerosol absorption coefficient, between 2007 and 2013, were made at the ground level in Évora, a Portuguese small town located in the southwestern Iberia Peninsula. Such a relatively long time series of absorbing aerosols is unique in Portugal and uncommon elsewhere. The average aerosol absorption coefficient was close to 9 Mm−1and clear cycles at both daily and seasonal time scales were found. An average increase by a factor of two (from 6 to 12 Mm−1) was observed in winter if compared to summer season. The daily variations were similarly shaped for all seasons, with two morning and afternoon peaks, but with magnitudes modulated by the seasonal evolution. That was not the case if Sundays were considered. These variations can be explained in terms of the impact of local particle sources, related mainly to traffic and biomass burning and upward mixing of the aerosol due to variable mixing layer heights, either daily or seasonally. Also, a strong negative correlation between the aerosol absorption coefficient and the wind speed was verified, and an exponential decay function was found to fit very well to the data. The wind direction seems to be not correlated with the aerosol absorption coefficient.

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What have we missed when studying the impact of aerosols on surface ozone via changing photolysis rates?

10.5194/acp-2020-140-ac2 ◽

2020 ◽

Author(s):

Jinhui Gao

Keyword(s):

Surface Ozone ◽

Photolysis Rates ◽

The Impact

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Impact of dust on tropospheric photochemistry over polluted regions: a case study of the Beijing megacity

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-20145-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 20145-20194 ◽

Cited By ~ 1

Author(s):

S. Zhu ◽

T. Butler ◽

R. Sander ◽

J. Ma ◽

M. G. Lawrence

Keyword(s):

Trace Gases ◽

Heterogeneous Reactions ◽

Rate Coefficients ◽

Mixing Ratio ◽

Air Masses ◽

Photolysis Rates ◽

Tropospheric Photochemistry ◽

Relative Change ◽

The Impact

Abstract. The box model MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere) is updated by incorporating detailed heterogeneous chemistry occurring on mineral aerosol surfaces. The model is used to investigate the impact of dust on tropospheric photochemistry, when the dust is transported to a polluted region together with other trace gases. The impacts of dust via heterogeneous removal of gases are analyzed for different hypothetical transport rates which are described by four different exchange rate coefficients Kt in the model. Substantial impacts are found for many gases, including Ox (O3+O(3P), NOx (NO+NO2) and OH. The Ox daily average mixing ratio decreases due to heterogeneous reactions on dust. The change ranges from –2.5 to –18.4 nmol/mol, and is larger for faster mixing with upwind air masses (i.e. greater Kt). This translates into a large relative change in Ox, ranging from –44% to –55%, which changes slightly with increasing values of Kt. By assuming an artificial 50% decrease of all photolysis rates, the impacts of dust via photolysis perturbation are also estimated. Furthermore, the uncertainties in the results due to the uncertainties in the uptake coefficients are evaluated. It is found that for all gases which are heterogeneously removed, the self-removal results in the largest uncertainty (e.g. –49% for O3, –76% for NO2, –47% for HNO3, –92% for HCHO, –64% for CH3OH and –93% for SO2). The heterogeneous removal of NO2 is found to be particularly important, because it results in significant uncertainties not only in itself, but also in OH (340%) and HO2 (365%). Moreover, the heterogeneous removal of HCHO and O3 also has farther-reaching effects on the OH concentration (resulting in changes of –55% and 45%, respectively), and the heterogeneous removal of HCHO results in an uncertainty of –38% in the HO2 concentration.

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Vertical variability of the properties of highly aged biomass burning aerosol transported over the southeast Atlantic during CLARIFY-2017

10.5194/acp-2020-197 ◽

2020 ◽

Cited By ~ 4

Author(s):

Huihui Wu ◽

Jonathan W. Taylor ◽

Kate Szpek ◽

Justin Langridge ◽

Paul I. Williams ◽

...

Keyword(s):

Biomass Burning ◽

Climate Models ◽

Marine Boundary Layer ◽

Regional Climate ◽

Single Scattering ◽

Important Region ◽

Absorbing Aerosols ◽

Lower Temperature ◽

The Impact ◽

Vertical Variability

Abstract. Seasonal biomass burning (BB) from June to October in central and southern Africa leads to absorbing aerosols being transported over the south Atlantic Ocean every year, and contributes significantly to the regional climate forcing. The vertical distribution of submicron aerosols and their properties were characterized over the remote southeast Atlantic for the first time, using airborne in-situ measurements made during the CLoud-Aerosol-Radiation Interactions and Forcing for Year 2017 (CLARIFY-2017) campaign. BB aerosols were intensively observed in the region surrounding Ascension Island, in the marine boundary layer (MBL) and free troposphere (FT) up to 5 km. We show that the aerosols had undergone a significant aging process during > 7 days transit from source, as indicated by highly oxidized organic aerosol and thickly coated black carbon (BC). The highly aged BB aerosols in the CLARIFY region were also especially rich in BC compared with those from other regions. We also found significant vertical variation in the single scattering albedos (SSA) of these aerosols, as a function of relative chemical composition and size. The lowest SSA was generally in the low FT layer around 2000 m altitude (medians: 0.83 at 405 nm and 0.80 at 658 nm). This finding is important since it means that BB aerosols across the east Atlantic region are more absorbing than is currently represented in climate models. Furthermore, in the FT, we show that SSA increased with altitude and this was associated with an enhanced inorganic nitrate mass fraction and aerosol size. This likely results from increased partitioning to the existing particles at higher altitude with lower temperature and higher relative humidity. After entrainment into the BL, aerosols were generally smaller in size than were observed in the FT, and had a larger fraction of scattering material with resultant higher average dry SSA, mostly due to marine emissions and aerosol removal by drizzle. Our results provide unique observational constraints on aerosol parameterizations used in modelling regional radiation interactions over this important region. We recommend that future work should consider the impact of this vertical variability on climate models.

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Solar “brightening” impact on summer surface ozone between 1990 and 2010 in Europe – a model sensitivity study of the influence of the aerosol–radiation interactions

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-9741-2018 ◽

2018 ◽

Vol 18 (13) ◽

pp. 9741-9765 ◽

Cited By ~ 3

Author(s):

Emmanouil Oikonomakis ◽

Sebnem Aksoyoglu ◽

Martin Wild ◽

Giancarlo Ciarelli ◽

Urs Baltensperger ◽

...

Keyword(s):

Air Quality ◽

Surface Ozone ◽

Biogenic Emissions ◽

Base Case ◽

Air Quality Model ◽

Quality Model ◽

Ozone Concentrations ◽

Photolysis Rates ◽

Ozone Trends ◽

The Impact

Abstract. Surface solar radiation (SSR) observations have indicated an increasing trend in Europe since the mid-1980s, referred to as solar “brightening”. In this study, we used the regional air quality model, CAMx (Comprehensive Air Quality Model with Extensions) to simulate and quantify, with various sensitivity runs (where the year 2010 served as the base case), the effects of increased radiation between 1990 and 2010 on photolysis rates (with the PHOT1, PHOT2 and PHOT3 scenarios, which represented the radiation in 1990) and biogenic volatile organic compound (BVOC) emissions (with the BIO scenario, which represented the biogenic emissions in 1990), and their consequent impacts on summer surface ozone concentrations over Europe between 1990 and 2010. The PHOT1 and PHOT2 scenarios examined the effect of doubling and tripling the anthropogenic PM2.5 concentrations, respectively, while the PHOT3 investigated the impact of an increase in just the sulfate concentrations by a factor of 3.4 (as in 1990), applied only to the calculation of photolysis rates. In the BIO scenario, we reduced the 2010 SSR by 3 % (keeping plant cover and temperature the same), recalculated the biogenic emissions and repeated the base case simulations with the new biogenic emissions. The impact on photolysis rates for all three scenarios was an increase (in 2010 compared to 1990) of 3–6 % which resulted in daytime (10:00–18:00 Local Mean Time – LMT) mean surface ozone differences of 0.2–0.7 ppb (0.5–1.5 %), with the largest hourly difference rising as high as 4–8 ppb (10–16 %). The effect of changes in BVOC emissions on daytime mean surface ozone was much smaller (up to 0.08 ppb, ∼ 0.2 %), as isoprene and terpene (monoterpene and sesquiterpene) emissions increased only by 2.5–3 and 0.7 %, respectively. Overall, the impact of the SSR changes on surface ozone was greater via the effects on photolysis rates compared to the effects on BVOC emissions, and the sensitivity test of their combined impact (the combination of PHOT3 and BIO is denoted as the COMBO scenario) showed nearly additive effects. In addition, all the sensitivity runs were repeated on a second base case with increased NOx emissions to account for any potential underestimation of modeled ozone production; the results did not change significantly in magnitude, but the spatial coverage of the effects was profoundly extended. Finally, the role of the aerosol–radiation interaction (ARI) changes in the European summer surface ozone trends was suggested to be more important when comparing to the order of magnitude of the ozone trends instead of the total ozone concentrations, indicating a potential partial damping of the effects of ozone precursor emissions' reduction.

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First multi-year occultation observations of CO<sub>2</sub> in the MLT by ACE satellite: observations and analysis using the extended CMAM

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-1133-2010 ◽

2010 ◽

Vol 10 (3) ◽

pp. 1133-1153 ◽

Cited By ~ 39

Author(s):

S. R. Beagley ◽

C. D. Boone ◽

V. I. Fomichev ◽

J. J. Jin ◽

K. Semeniuk ◽

...

Keyword(s):

Middle Atmosphere ◽

Formation Rate ◽

Lower Thermosphere ◽

Eddy Diffusion ◽

Photolysis Rates ◽

Candidate Species ◽

Rocket Measurements ◽

The Impact ◽

Co Observations

Abstract. This paper presents the first global set of observations of CO2 in the mesosphere and lower thermosphere (MLT) obtained by the ACE-FTS instrument on SCISAT-I, a small Canadian satellite launched in 2003. The observations use the solar occultation technique and document the fall-off in the mixing ratio of CO2 in the MLT region. The beginning of the fall-off of the CO2, or "knee" occurs at about 78 km and lies higher than in the CRISTA-1 measurements (~70 km) but lower than in the SABER 1.06 (~80 km) and much lower than in rocket measurements. We also present the measurements of CO obtained concurrently which provide important constraints for analysis. We have compared the ACE measurements with simulations of the CO2 and CO distributions in the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). Applying standard chemistry we find that we cannot get agreement between the model and ACE CO2 observations although the CO observations are adequately reproduced. There appears to be about a 10 km offset compared to the observed ACE CO2, with the model "knee" occurring too high. In analyzing the disagreement, we have investigated the variation of several parameters of interest (photolysis rates, formation rate for CO2, and the impact of uncertainty in turbulent eddy diffusion) in order to explore parameter space for this problem. Our conclusions are that there must be a loss process for CO2, about 2–4~times faster than photolysis that will sequester the carbon in some form other than CO and we have speculated on the role of meteoritic dust as a possible candidate. In addition, from this study we have highlighted a possible important role for unresolved vertical eddy diffusion in 3-D models in determining the distribution of candidate species in the mesosphere which requires further study.

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