Distinct wind convergence patterns due to thermal and momentum forcing of the low level jet into the Mexico City basin

Abstract. Mexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A low level jet entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the jet. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The low level jet is found to occur on most days of the campaign and is primarily due to thermal forcing which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the jet and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to stronger jets and a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere.

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Distinct wind convergence patterns in the Mexico City basin due to the interaction of the gap winds with the synoptic flow

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-1249-2006 ◽

2006 ◽

Vol 6 (5) ◽

pp. 1249-1265 ◽

Cited By ~ 47

Author(s):

B. de Foy ◽

A. Clappier ◽

L. T. Molina ◽

M. J. Molina

Keyword(s):

Air Quality ◽

Mexico City ◽

Land Surface ◽

Regional Scale ◽

Meteorological Conditions ◽

Urban Atmosphere ◽

Simple Method ◽

Convergence Line ◽

Early Afternoon ◽

The City

Abstract. Mexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A gap wind entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the gap wind. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The gap wind is found to occur on most days of the campaign and is the result of a temperature gradient across the southern basin rim which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the flow and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to both stronger gap flows due to channelling and winds over the southern and western basin rim. This results in a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere.

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Nocturnal Low-Level Jet in a Mountain Basin Complex. Part II: Transport and Diffusion of Tracer under Stable Conditions

Journal of Applied Meteorology and Climatology ◽

10.1175/jam2367.1 ◽

2006 ◽

Vol 45 (5) ◽

pp. 740-753 ◽

Cited By ~ 27

Author(s):

Lisa S. Darby ◽

K. Jerry Allwine ◽

Robert M. Banta

Keyword(s):

Surface Pressure ◽

Salt Lake ◽

Low Level ◽

Stable Conditions ◽

Basin Scale ◽

Flow Features ◽

Transport And Diffusion ◽

Low Level Jet ◽

The City ◽

And Diffusion

Abstract Differences in nighttime transport and diffusion of sulfur hexafluoride (SF6) tracer in an urban complex-terrain setting (Salt Lake City, Utah) are investigated using surface and Doppler lidar wind data and large-scale surface pressure differences. Interacting scales of motion, as studied through the URBAN 2000 field program combined with the Vertical Transport and Mixing (VTMX) experiment, explained the differences in the tracer behavior during three separate intensive operating periods. With an emphasis on nighttime stable boundary layer conditions, these field programs were designed to study flow features responsible for the nighttime transport of airborne substances. This transport has implications for air quality, homeland security, and emergency response if the airborne substances are hazardous. The important flow features investigated included thermally forced canyon and slope flows and a low-level jet (LLJ) that dominated the basin-scale winds when the surface pressure gradient was weak. The presence of thermally forced flows contributed to the complexity and hindered the predictability of the tracer motion within and beyond the city. When organized thermally forced flows were present, the tracer tended to stay closer to the city for longer periods of time, even though a strong basin-scale LLJ did develop. When thermally forced flows were short lived or absent, the basin-scale low-level jet dominated the wind field and enhanced the transport of tracer material out of the city.

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Contribution of Local and Transboundary Air Pollution to the Urban Air Quality of Fukuoka, Japan

Atmosphere ◽

10.3390/atmos12040431 ◽

2021 ◽

Vol 12 (4) ◽

pp. 431

Author(s):

Ayako Yoshino ◽

Akinori Takami ◽

Keiichiro Hara ◽

Chiharu Nishita-Hara ◽

Masahiko Hayashi ◽

...

Keyword(s):

Air Pollution ◽

Air Quality ◽

Urban Areas ◽

Air Pollutants ◽

Regional Scale ◽

Gaseous Species ◽

Transboundary Air Pollution ◽

Local Air Pollution ◽

The City

Transboundary air pollution (TAP) and local air pollution (LAP) influence the air quality of urban areas. Fukuoka, located on the west side of Japan and affected by TAP from the Asian continent, is a unique example for understanding the contribution of LAP and TAP. Gaseous species and particulate matter (PM) were measured for approximately three weeks in Fukuoka in the winter of 2018. We classified two distinctive periods, LAP and TAP, based on wind speed. The classification was supported by variations in the concentration of gaseous species and by backward trajectories. Most air pollutants, including NOx and PM, were high in the LAP period and low in the TAP period. However, ozone was the exception. Therefore, our findings suggest that reducing local emissions is necessary. Ozone was higher in the TAP period, and the variation in ozone concentration was relatively small, indicating that ozone was produced outside of the city and transported to Fukuoka. Thus, air pollutants must also be reduced at a regional scale, including in China.

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NESTED HIGH-RESOLUTION NOx AND PM SIMULATIONS OVER ZÜRICH

10.5194/egusphere-egu21-6202 ◽

2021 ◽

Author(s):

Ivo Suter ◽

Lukas Emmenegger ◽

Dominik Brunner

Keyword(s):

Air Pollution ◽

Air Quality ◽

Boundary Conditions ◽

Meteorological Conditions ◽

Model Systems ◽

Multi Scale ◽

Wide Range ◽

The Impact ◽

The City ◽

Concentration Levels

Reducing air pollution, which is the world's largest single environmental health risk, demands better-informed air quality policies. Consequently, multi-scale air quality models are being developed with the goal to resolve cities. One of the major challenges in such model systems is to accurately represent all large- and regional-scale processes that may critically determine the background concentration levels over a given city. This is particularly true for longer-lived species such as aerosols, for which background levels often dominate the concentration levels, even within the city. Furthermore, the heterogeneous local emissions, and complex dispersion in the city have to be considered carefully.In this study, the impact of processes across a wide range of scales on background concentrations over Switzerland and the city of Zurich was modelled by performing one year of nested European and Swiss national COSMO-ART simulations to obtain adequate boundary conditions for gas-phase chemical, aerosol and meteorological conditions for city-resolving simulations. The regional climate chemistry model COSMO-ART (Vogel et al. 2009) was used in a 1-way coupled mode. The outer, European, domain, which was driven by chemical boundary conditions from the global MOZART model, had a 6.6 km horizontal resolution and the inner, Swiss, domain one of 2.2 km. For the city scale, a catalogue of more than 1000 mesoscale flow patterns with 100 m resolution was created with the model GRAMM, based on a discrete set of atmospheric stabilities, wind speeds and directions, accounting for the influence of land-use and topography. Finally, the flow around buildings was solved with the CFD model GRAL forced at the boundaries by GRAMM. Subsequently, Lagrangian dispersion simulations for a set of air pollutants and emission sectors (traffic, industry, ...) based on extremely detailed building and emission data was performed in GRAL. The result of this nested procedure is a library of 3-dimensional air pollution maps representative of hourly situations in Zurich (Berchet et al. 2017). From these pre-computed situations, time-series and concentration maps can be obtained by selecting situations according to observed or modelled meteorological conditions.The results were compared to measurements from air quality monitoring network stations. Modelled concentrations of NOx and PM compared well to measurements across multiple locations, provided background conditions were considered carefully. The nested multi-scale modelling system COSMO-ART/GRAMM/GRAL can adequately reproduce local air quality and help understanding the relative contributions of local versus distant emissions, as well as fill the space between precise point measurements from monitoring sites. This information is useful for research, policy-making, and epidemiological studies particularly under the assumption that exceedingly high concentrations become more and more localised phenomenon in the future.

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Simulations of organic aerosol concentrations in Mexico City using the WRF-CHEM model during the MCMA-2006/MILAGRO campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-3789-2011 ◽

2011 ◽

Vol 11 (8) ◽

pp. 3789-3809 ◽

Cited By ~ 97

Author(s):

G. Li ◽

M. Zavala ◽

W. Lei ◽

A. P. Tsimpidi ◽

V. A. Karydis ◽

...

Keyword(s):

Urban Area ◽

Mexico City ◽

Aging Process ◽

Organic Aerosol ◽

Suburban Area ◽

Traditional Model ◽

Background Site ◽

Organic Components ◽

Early Afternoon ◽

The City

Abstract. Organic aerosol concentrations are simulated using the WRF-CHEM model in Mexico City during the period from 24 to 29 March in association with the MILAGRO-2006 campaign. Two approaches are employed to predict the variation and spatial distribution of the organic aerosol concentrations: (1) a traditional 2-product secondary organic aerosol (SOA) model with non-volatile primary organic aerosols (POA); (2) a non-traditional SOA model including the volatility basis-set modeling method in which primary organic components are assumed to be semi-volatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. The MCMA (Mexico City Metropolitan Area) 2006 official emission inventory is used in simulations and the POA emissions are modified and distributed by volatility based on dilution experiments for the non-traditional SOA model. The model results are compared to the Aerosol Mass Spectrometry (AMS) observations analyzed using the Positive Matrix Factorization (PMF) technique at an urban background site (T0) and a suburban background site (T1) in Mexico City. The traditional SOA model frequently underestimates the observed POA concentrations during rush hours and overestimates the observations in the rest of the time in the city. The model also substantially underestimates the observed SOA concentrations, particularly during daytime, and only produces 21% and 25% of the observed SOA mass in the suburban and urban area, respectively. The non-traditional SOA model performs well in simulating the POA variation, but still overestimates during daytime in the urban area. The SOA simulations are significantly improved in the non-traditional SOA model compared to the traditional SOA model and the SOA production is increased by more than 100% in the city. However, the underestimation during daytime is still salient in the urban area and the non-traditional model also fails to reproduce the high level of SOA concentrations in the suburban area. In the non-traditional SOA model, the aging process of primary organic components considerably decreases the OH levels in simulations and further impacts the SOA formation. If the aging process in the non-traditional model does not have feedback on the OH in the gas-phase chemistry, the SOA production is enhanced by more than 10% compared to the simulations with the OH feedback during daytime, and the gap between the simulations and observations in the urban area is around 3 μg m−3 or 20% on average during late morning and early afternoon, within the uncertainty from the AMS measurements and PMF analysis. In addition, glyoxal and methylglyoxal can contribute up to approximately 10% of the observed SOA mass in the urban area and 4% in the suburban area. Including the non-OH feedback and the contribution of glyoxal and methylglyoxal, the non-traditional SOA model can explain up to 83% of the observed SOA in the urban area, and the underestimation during late morning and early afternoon is reduced to 0.9 μg m−3 or 6% on average. Considering the uncertainties from measurements, emissions, meteorological conditions, aging of semi-volatile and intermediate volatile organic compounds, and contributions from background transport, the non-traditional SOA model is capable of closing the gap in SOA mass between measurements and models.

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Particulate polycyclic aromatic hydrocarbon spatial variability and aging in Mexico City

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-15693-2007 ◽

2007 ◽

Vol 7 (6) ◽

pp. 15693-15721 ◽

Cited By ~ 1

Author(s):

D. A. Thornhill ◽

S. C. Herndon ◽

T. B. Onasch ◽

E. C. Wood ◽

M. Zavala ◽

...

Keyword(s):

Los Angeles ◽

Mexico City ◽

Regional Scale ◽

Active Surface ◽

Heterogeneous Reactions ◽

Active Surface Area ◽

Spatial And Temporal Patterns ◽

Gaseous Species ◽

Polycyclic Aromatic ◽

The City

Abstract. As part of the Megacities Initiative: Local and Global Research Observations (MILAGRO) study in the Mexico City Metropolitan Area in March 2006, we measured particulate polycyclic aromatic hydrocarbons (PAHs) and other gaseous species and particulate properties at six locations throughout the city. The measurements were intended to support the following objectives: to describe spatial and temporal patterns in PAH concentrations, to gain insight into sources and transformations of PAHs, and to quantify the relationships between PAHs and other pollutants. Total particulate PAHs at the Instituto Mexicano del Petróleo (T0 supersite) located near downtown averaged 50 ng m−3, and aerosol active surface area averaged 80 mm2 m−3. PAHs were also measured on board the Aerodyne Mobile Laboratory, which visited six sites encompassing a mixture of different land uses and a range of ages of air parcels transported from the city core. Weak intersite correlations suggest that local sources are important and variable and that exposure to PAHs cannot be represented by a single regional-scale value. The relationships between PAHs and other pollutants suggest that a variety of sources and ages of particles are present. Among carbon monoxide, nitrogen oxides (NOx), and carbon dioxide, particulate PAHs are most strongly correlated with NOx. Mexico City's PAH-to-black carbon mass ratio of 0.01 is similar to that found on a freeway loop in the Los Angeles area and approximately 8–30 times higher than that found in other cities. Ratios also indicate that primary combustion particles are rapidly coated by secondary aerosol in Mexico City. If so, the lifetime of PAHs may be prolonged if the coating protects them against photodegradation or heterogeneous reactions.

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The interaction between the nocturnal Amazonian low-level jet and convection in CESM

Journal of Climate ◽

10.1175/jcli-d-21-0042.1 ◽

2021 ◽

pp. 1-37

Author(s):

Hedanqiu Bai ◽

Courtney Schumacher

Keyword(s):

Air Temperature ◽

Climate Models ◽

Coupled Model ◽

Reanalysis Data ◽

Equatorial Atlantic ◽

Cold Air ◽

Low Level ◽

Temperature Bias ◽

Early Afternoon ◽

Low Level Jet

AbstractA nocturnal Amazonian low-level jet (ALLJ) was recently diagnosed using reanalysis data. This work assesses the ability of CESM1.2.2 to reproduce the jet and explores the mechanisms by which the ALLJ influences convection in the Amazon. The coupled CESM simulates the nocturnal ALLJ realistically, while CAM5 does not. A low-level cold air temperature bias in the eastern Amazon exists in CAM5, thus the ALLJ is weaker than observed. However, a cold SST bias over the equatorial North Atlantic in the coupled model offsets the cold air temperature bias, producing a realistic ALLJ. Climate models significantly underestimate March-April-May (MAM) precipitation over the eastern Amazon. We ran two sensitivity experiments using the coupled CESM by adding bottom-heavy diabatic heating at noon and midnight for 2.5 hours along the coastal Amazon during MAM to mimic the occurrence of shallow precipitating convection. When heating is added during the early afternoon, coastal convection deepens and the ALLJ transports moisture inland from the ocean, preconditioning the environment for deep convective development during the ensuing hours. The increased convection over the eastern Amazon also moderately alleviates the equatorial Atlantic westerly wind bias, leading to deepening of the east Atlantic thermocline in the following months and partially improving the simulated June-July-August (JJA) Atlantic cold tongue in the coupled model. When heating is added at night, coastal convection does not strengthen as much and the ALLJ transports less moisture. Improvements in the simulated Atlantic winds and SST are negligible. Therefore, diurnal circulations matter to the organization of convection and rain across the Amazon, with impacts over the equatorial Atlantic.

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Comparison of measurements of peroxyacyl nitrates and primary carbonaceous aerosol concentrations in Mexico City determined in 1997 and 2003

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-2277-2007 ◽

2007 ◽

Vol 7 (9) ◽

pp. 2277-2285 ◽

Cited By ~ 39

Author(s):

N. A. Marley ◽

J. S. Gaffney ◽

R. Ramos-Villegas ◽

B. Cárdenas González

Keyword(s):

Air Quality ◽

Black Carbon ◽

Mexico City ◽

Elemental Carbon ◽

Control Strategies ◽

Ambient Air ◽

Daily Maximum ◽

Atmospheric Measurements ◽

Important Species ◽

The City

Abstract. The concentrations of peroxyacetyl nitrate (PAN) in ambient air can be a good indicator of air quality and the effectiveness of control strategies for reducing ozone levels in urban areas. As PAN is formed by the oxidation of reactive hydrocarbons in the presence of nitrogen dioxide (NO2), it is a direct measure of the peroxyacyl radical levels produced from reactive organic emissions in the urban air shed. Carbon soot, known as black carbon (BC) or elemental carbon (EC), is a primary atmospheric aerosol species and is a good indicator of the levels of combustion emissions, particularly from diesel engines, in major cities. Mexico City is the second largest megacity in the world and has long suffered from poor air quality. Reported here are atmospheric measurements of PAN and BC obtained in Mexico City during the Mexico Megacity 2003 field study. These results are compared with measurements obtained earlier during the Investigación sobre Materia Particulada y Deterioro Atmosférico – Aerosol and Visibility Research (IMADA-AVER) campaign in 1997 to obtain an estimate of the changes in emissions in Mexico City and the effectiveness of control strategies adopted during that time. Concentrations of PAN in 1997 reached a maximum of 34 ppb with an average daily maximum of 15 ppb. The PAN levels recorded in 2003 were quite different, with an average daily maximum of 3 ppb. This dramatic reduction in PAN levels observed in 2003 indicate that reactive hydrocarbon emissions have been reduced in the city due to controls on olefins in liquefied petroleum gas (LPG) and also due to the significant number of newer vehicles with catalytic converters that have replaced older higher emission vehicles. In contrast, black/elemental carbon levels were similar in 1997 and 2003 indicating little improvement likely due to the lack of controls on diesel vehicles in the city. Thus, while air quality and ozone production have improved, Mexico City and other megacities continue to be a major source of black carbon aerosols, which can be an important species in determining regional radiative balance and climate.

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Modeling organic aerosols during MILAGRO: application of the CHIMERE model and importance of biogenic secondary organic aerosols

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-12207-2009 ◽

2009 ◽

Vol 9 (3) ◽

pp. 12207-12281 ◽

Cited By ~ 7

Author(s):

A. Hodzic ◽

J. L. Jimenez ◽

S. Madronich ◽

A. C. Aiken ◽

B. Bessagnet ◽

...

Keyword(s):

Mexico City ◽

Biomass Burning ◽

Transport Model ◽

Large Fraction ◽

Regional Scale ◽

Organic Aerosols ◽

Base Case ◽

Surface Model ◽

Near Surface ◽

The City

Abstract. The meso-scale chemistry-transport model CHIMERE is used to assess our understanding of major sources and formation processes leading to a fairly large amount of organic aerosols (OA, including primary OA (POA) and secondary OA (SOA)) observed in Mexico City during the MILAGRO field project (March 2006). Chemical analyses of submicron aerosols from aerosol mass spectrometers (AMS) indicate that organic particles found in the Mexico City basin contain a large fraction of oxygenated organic species (OOA) which have strong correspondence with SOA, and that their production actively continues downwind of the city. The SOA formation is modeled here by the one-step oxidation of anthropogenic (i.e. aromatics, alkanes), biogenic (i.e. monoterpenes and isoprene), and biomass-burning SOA precursors and their partitioning into both organic and aqueous phases. The near-surface model evaluation shows that predicted OA correlates reasonably well with measurements during the campaign, however it remains a factor of 2 lower than the measured total OA. Fairly good agreement is found between predicted and observed POA within the city suggesting that anthropogenic and biomass burning emissions are reasonably captured. Consistent with previous studies in Mexico City, large discrepancies are encountered for SOA, with a factor of 2–10 model underestimate. When only anthropogenic SOA precursors were considered, the model was able to reproduce within a factor of two the sharp increase in SOA concentrations during the late morning at both urban and near-urban locations but the discrepancy increases rapidly later in the day, consistent with previous results, and is especially obvious when the column-integrated SOA mass is considered instead of the surface concentration. The increase in the missing SOA mass in the afternoon coincides with the sharp drop in POA suggesting a tendency of the model to excessively evaporate the freshly formed SOA. Predicted SOA concentrations in our base case were extremely low when photochemistry was not active, especially overnight, as the SOA formed in the previous day was mostly quickly advected away from the basin. These nighttime discrepancies were not significantly reduced when greatly enhanced partitioning to the aerosol phase was assumed. Model sensitivity results suggest that observed nighttime SOA concentrations are strongly influenced by a regional background SOA (~1.5 μg/m3) of biogenic origin which is transported from the coastal mountain ranges into the Mexico City basin. The relative contribution of biogenic SOA to monthly mean modeled SOA levels is estimated to be more than 30% within the city and up to 65–90% at the regional scale (even in the immediate vicinity of the city) which may help explain the significant amount of modern carbon in the aerosols inside the city during low biomass burning periods. The anthropogenic emissions of isoprene and its nighttime oxidation by NO3 were also found to enhance the SOA mean concentrations within the city by an additional 15%. Our results confirm the large underestimation of the SOA production by traditional models in polluted regions (estimated as 10–20 Tons within the Mexico City metropolitan area during the daily peak), and emphasize for the first time the role of biogenic precursors in this region, indicating that they cannot be neglected in modeling studies.

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Simulations of organic aerosol concentrations in Mexico City using the WRF-CHEM model during the MCMA-2006/MILAGRO campaign

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-29349-2010 ◽

2010 ◽

Vol 10 (12) ◽

pp. 29349-29404 ◽

Cited By ~ 1

Author(s):

G. Li ◽

M. Zavala ◽

W. Lei ◽

A. P. Tsimpidi ◽

V. A. Karydis ◽

...

Keyword(s):

Urban Area ◽

Mexico City ◽

Aging Process ◽

Organic Aerosol ◽

Suburban Area ◽

Traditional Model ◽

Background Site ◽

Organic Components ◽

Early Afternoon ◽

The City

Abstract. Organic aerosol concentrations are simulated using the WRF-CHEM model in Mexico City during the period from 24 to 29 March in association with the MILAGRO-2006 campaign. Two approaches are employed to predict the variation and spatial distribution of the organic aerosol concentrations: (1) a traditional 2-product secondary organic aerosol (SOA) model with non-volatile primary organic aerosols (POA); (2) a non-traditional SOA model including the volatility basis-set modeling method in which primary organic components are assumed to be semi-volatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. The MCMA 2006 official emission inventory is used in simulations and the POA emissions are modified and distributed by volatility based on dilution experiments for the non-traditional SOA model. The model results are compared to the Aerosol Mass Spectrometry (AMS) observations analyzed using the Positive Matrix Factorization (PMF) technique at an urban background site (T0) and a suburban background site (T1) in Mexico City. The traditional SOA model frequently underestimates the observed POA concentrations during rush hours and overestimates the observations in the rest of the time in the city. The model also substantially underestimates the observed SOA concentrations, particularly during daytime, and only produces 21% and 25% of the observed SOA mass in the suburban and urban area, respectively. The non-traditional SOA model performs well in simulating the POA variation, but still overestimates during daytime in the urban area. The SOA simulations are significantly improved in the non-traditional SOA model compared to the traditional SOA model and the SOA production is increased by more than 100% in the city. However, the underestimation during daytime is still salient in the urban area and the non-traditional model also fails to reproduce the high level of SOA concentrations in the suburban area. In the non-traditional SOA model, the aging process of primary organic components considerably decreases the OH levels in simulations and further impacts the SOA formation. If the aging process in the non-traditional model does not have feedback on the OH in the gas-phase chemistry, the SOA production is enhanced by more than 10% compared to the simulations with the OH feedback during daytime, and the gap between the simulations and observations in the urban area is around 3 μg m−3 or 20% on average during late morning and early afternoon, within the uncertainty from the AMS measurements and PMF analysis. In addition, glyoxal and methylglyoxal can contribute up to approximately 10% of the observed SOA mass in the urban area and 4% in the suburban area. Including the non-OH feedback and the contribution of glyoxal and methylglyoxal, the non-traditional SOA model can explain up to 83% of the observed SOA in the urban area, and the underestimation during late morning and early afternoon is reduced to 0.9 μg m−3 or 6% on average. Considering the uncertainties from measurements, emissions, meteorological conditions, aging of SOA from anthropogenic VOCs, and contributions from background transport, the non-traditional SOA model is capable of closing the gap in SOA mass between measurements and models.

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