Chemically-resolved aerosol eddy covariance flux measurements in urban Mexico City during MILAGRO 2006

Abstract. As part of the MILAGRO 2006 field campaign, the exchange of atmospheric aerosols with the urban landscape was measured from a tall tower erected in a heavily populated neighborhood of Mexico City. Urban submicron aerosol fluxes were measured using an eddy covariance method with a quadrupole aerosol mass spectrometer during a two week period in March 2006. Nitrate and ammonium aerosol concentrations were elevated at this location near the city center compared to measurements at other urban sites. Significant downward fluxes of nitrate aerosol, averaging −0.2 μg m−2 s−1, were measured during daytime. The urban surface was not a significant source of sulfate aerosols. The measurements also showed that primary organic aerosol fluxes, approximated by hydrocarbon-like organic aerosols (HOA), displayed diurnal patterns similar to CO2 fluxes and anthropogenic urban activities. Overall, 47% of submicron organic aerosol emissions were HOA, 35% were oxygenated (OOA) and 18% were associated with biomass burning (BBOA). Organic aerosol fluxes were bi-directional, but on average HOA fluxes were 0.09 μg m−2 s−1, OOA fluxes were −0.002 μg m−2 s−1, and BBOA fluxes were −0.03 μg m−2 s−1. The average diurnal flux results showed that the 2006 gridded emissions inventory of Mexico City underestimates mid-day and evening rush hour emissions of submicron aerosols for the monitored neighborhood, but averaged daily, the emission inventory and flux measurements for this location were in close agreement.

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Chemically-resolved aerosol eddy covariance flux measurements in urban Mexico City during MILAGRO 2006

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-7809-2012 ◽

2012 ◽

Vol 12 (16) ◽

pp. 7809-7823 ◽

Cited By ~ 10

Author(s):

R. Zalakeviciute ◽

M. L. Alexander ◽

E. Allwine ◽

J. L. Jimenez ◽

B. T. Jobson ◽

...

Keyword(s):

Eddy Covariance ◽

Mexico City ◽

Atmospheric Aerosols ◽

Emission Inventory ◽

Urban Landscape ◽

Organic Aerosol ◽

Emission Rates ◽

Eddy Covariance Method ◽

Emissions Inventory ◽

Flux Measurements

Abstract. As part of the MILAGRO 2006 field campaign, the exchange of atmospheric aerosols with the urban landscape was measured from a tall tower erected in a heavily populated neighborhood of Mexico City. Urban submicron aerosol fluxes were measured using an eddy covariance method with a quadrupole aerosol mass spectrometer during a two week period in March, 2006. Nitrate and ammonium aerosol concentrations were elevated at this location near the city center compared to measurements at other urban sites. Significant downward fluxes of nitrate aerosol, averaging −0.2 μg m−2 s−1, were measured during daytime. The urban surface was not a significant source of sulfate aerosols. The measurements also showed that primary organic aerosol fluxes, approximated by hydrocarbon-like organic aerosols (HOA), displayed diurnal patterns similar to CO2 fluxes and anthropogenic urban activities. Overall, 47% of submicron organic aerosol emissions were HOA, 35% were oxygenated (OOA) and 18% were associated with biomass burning (BBOA). Organic aerosol fluxes were bi-directional, but on average HOA fluxes were 0.1 μg m−2 s−1, OOA fluxes were −0.03 μg m−2 s−1, and BBOA fluxes were −0.03 μg m−2 s−1. After accounting for size differences (PM1 vs PM2.5) and using an estimate of the black carbon component, comparison of the flux measurements with the 2006 gridded emissions inventory of Mexico City, showed that the daily-averaged total PM emission rates were essentially identical for the emission inventory and the flux measurements. However, the emission inventory included dust and metal particulate contributions, which were not included in the flux measurements. As a result, it appears that the inventory underestimates overall PM emissions for this location.

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Eddy covariance flux measurements of pollutant gases in urban Mexico City

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-7325-2009 ◽

2009 ◽

Vol 9 (19) ◽

pp. 7325-7342 ◽

Cited By ~ 83

Author(s):

E. Velasco ◽

S. Pressley ◽

R. Grivicke ◽

E. Allwine ◽

T. Coons ◽

...

Keyword(s):

Eddy Covariance ◽

Mexico City ◽

Atmospheric Chemistry ◽

Anthropogenic Activities ◽

Flux Measurement ◽

Proton Transfer Reaction ◽

Surface Exchange ◽

Emissions Inventory ◽

Flux Measurements ◽

Local Emissions

Abstract. Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded local emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The results show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not reported in the mobile emissions inventory.

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Eddy covariance flux measurements of pollutant gases in urban Mexico City

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-7991-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 7991-8034 ◽

Cited By ~ 4

Author(s):

E. Velasco ◽

S. Pressley ◽

R. Grivicke ◽

E. Allwine ◽

T. Coons ◽

...

Keyword(s):

Eddy Covariance ◽

Mexico City ◽

Atmospheric Chemistry ◽

Anthropogenic Activities ◽

Flux Measurement ◽

Proton Transfer Reaction ◽

Surface Exchange ◽

Emissions Inventory ◽

Flux Measurements ◽

Residential District

Abstract. Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The data show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not present in the mobile emissions inventory.

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Constraining condensed-phase formation kinetics of secondary organic aerosol components from isoprene epoxydiols

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-1245-2016 ◽

2016 ◽

Vol 16 (3) ◽

pp. 1245-1254 ◽

Cited By ~ 31

Author(s):

T. P. Riedel ◽

Y.-H. Lin ◽

Z. Zhang ◽

K. Chu ◽

J. A. Thornton ◽

...

Keyword(s):

Aqueous Phase ◽

Atmospheric Aerosols ◽

Rate Constants ◽

Reaction Rate ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Heterogeneous Reactions ◽

Model Calculations ◽

Reaction Rate Constants ◽

Aerosol Mass

Abstract. Isomeric epoxydiols from isoprene photooxidation (IEPOX) have been shown to produce substantial amounts of secondary organic aerosol (SOA) mass and are therefore considered a major isoprene-derived SOA precursor. Heterogeneous reactions of IEPOX on atmospheric aerosols form various aerosol-phase components or "tracers" that contribute to the SOA mass burden. A limited number of the reaction rate constants for these acid-catalyzed aqueous-phase tracer formation reactions have been constrained through bulk laboratory measurements. We have designed a chemical box model with multiple experimental constraints to explicitly simulate gas- and aqueous-phase reactions during chamber experiments of SOA growth from IEPOX uptake onto acidic sulfate aerosol. The model is constrained by measurements of the IEPOX reactive uptake coefficient, IEPOX and aerosol chamber wall losses, chamber-measured aerosol mass and surface area concentrations, aerosol thermodynamic model calculations, and offline filter-based measurements of SOA tracers. By requiring the model output to match the SOA growth and offline filter measurements collected during the chamber experiments, we derive estimates of the tracer formation reaction rate constants that have not yet been measured or estimated for bulk solutions.

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Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-8377-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 8377-8427 ◽

Cited By ~ 2

Author(s):

A. C. Aiken ◽

D. Salcedo ◽

M. J. Cubison ◽

J. A. Huffman ◽

P. F. DeCarlo ◽

...

Keyword(s):

High Resolution ◽

Mexico City ◽

Biomass Burning ◽

Emissions Inventory ◽

Secondary Sources ◽

Diurnal Cycles ◽

Aerosol Mass ◽

Aerosol Mass Spectrometry ◽

Order Of Magnitude ◽

Primary Emissions

Abstract. Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and complementary instrumentation. Mass concentrations, diurnal cycles, and size distributions of inorganic and organic species are similar to results from the CENICA supersite in April 2003 with organic aerosol (OA) comprising about half of the fine PM mass. Positive Matrix Factorization (PMF) analysis of the high resolution OA spectra identified three major components: chemically-reduced urban primary emissions (hydrocarbon-like OA, HOA), oxygenated OA (OOA, mostly secondary OA or SOA), and biomass burning OA (BBOA) that correlates with levoglucosan and acetonitrile. BBOA includes several very large plumes from regional fires and likely also some refuse burning. A fourth OA component is a small local nitrogen-containing reduced OA component (LOA) which accounts for 9% of the OA mass but one third of the organic nitrogen, likely as amines. OOA accounts for almost half of the OA on average, consistent with previous observations. OA apportionment results from PMF-AMS are compared to the PM2.5 chemical mass balance of organic molecular markers (CMB-OMM, from GC/MS analysis of filters). Results from both methods are overall consistent. Both assign the major components of OA to primary urban, biomass burning/woodsmoke, and secondary sources at similar magnitudes. The 2006 Mexico City emissions inventory underestimates the urban primary PM2.5 emissions by a factor of ~4, and it is ~16 times lower than afternoon concentrations when secondary species are included. Additionally, the forest fire contribution is underestimated by at least an order-of-magnitude in the inventory.

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Options to correct local turbulent flux measurements for large-scale fluxes using a LES-based approach

10.5194/amt-2021-126 ◽

2021 ◽

Author(s):

Matthias Mauder ◽

Andreas Ibrom ◽

Luise Wanner ◽

Frederik De Roo ◽

Peter Brugger ◽

...

Keyword(s):

Eddy Covariance ◽

Large Scale ◽

Heat Fluxes ◽

Eddy Covariance Method ◽

Boundary Layer Height ◽

Secondary Circulations ◽

Low Pass ◽

Measurement Height ◽

Flux Measurements ◽

Dispersive Fluxes

Abstract. The eddy-covariance method provides the most direct estimates for fluxes between ecosystems and the atmosphere. However, dispersive fluxes can occur in the presence of secondary circulations, which can inherently not be captured by such single-tower measurements. In this study, we present options to correct local flux measurements for such large-scale transport based on a non-local parametric model that has been developed from a set of idealized LES runs for three real-world sites. The test sites DK-Sor, DE-Fen, and DE-Gwg, represent typical conditions in the mid-latitudes with different measurement height, different terrain complexity and different landscape-scale heterogeneity. Different ways to determine the boundary-layer height, which is a necessary input variable for modelling the dispersive fluxes, are applied, either from operational radio-soundings and local in-situ measurements for the flat site or from backscatter-intensity profile obtained from collocated ceilometers for the two sites in complex terrain. The adjusted total fluxes are evaluated by assessing the improvement in energy balance closure and by comparing the resulting latent heat fluxes with evapotranspiration rates from nearby lysimeters. The results show that not only the accuracy of the flux estimates is improved but also the precision, which is indicated by RMSE values that are reduced by approximately 50 %. Nevertheless, it needs to be clear that this method is intended to correct for a bias in eddy-covariance measurements due to the presence of large-scale dispersive fluxes. Other reasons potentially causing a systematic under- or overestimation, such as low-pass filtering effects and missing storage terms, still need to be considered and minimized as much as possible. Moreover, additional transport induced by surface heterogeneities is not considered.

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Constraining condensed-phase formation kinetics of secondary organic aerosol components from isoprene epoxydiols

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-28289-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 28289-28316 ◽

Cited By ~ 2

Author(s):

T. P. Riedel ◽

Y.-H. Lin ◽

Z. Zhang ◽

K. Chu ◽

J. A. Thornton ◽

...

Keyword(s):

Aqueous Phase ◽

Atmospheric Aerosols ◽

Rate Constants ◽

Reaction Rate ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Heterogeneous Reactions ◽

Model Calculations ◽

Reaction Rate Constants ◽

Aerosol Mass

Abstract. Isomeric epoxydiols from isoprene photooxidation (IEPOX) have been shown to produce substantial amounts of secondary organic aerosol (SOA) mass and are therefore considered a major isoprene-derived SOA precursor. Heterogeneous reactions of IEPOX on atmospheric aerosols form various aerosol-phase components or "tracers" that contribute to the SOA mass burden. A limited number of the reaction rate constants for these acid-catalyzed aqueous-phase tracer formation reactions have been constrained through bulk laboratory measurements. We have designed a chemical box model with multiple experimental constraints to explicitly simulate gas- and aqueous-phase reactions during chamber experiments of SOA growth from IEPOX uptake onto acidic sulfate aerosol. The model is constrained by measurements of the IEPOX reactive uptake coefficient, IEPOX and aerosol chamber wall-losses, chamber-measured aerosol mass and surface area concentrations, aerosol thermodynamic model calculations, and offline filter-based measurements of SOA tracers. By requiring the model output to match the SOA growth and offline filter measurements collected during the chamber experiments, we derive estimates of the tracer formation reaction rate constants that have not yet been measured or estimated for bulk solutions.

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Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

Atmospheric Measurement Techniques ◽

10.5194/amt-11-6075-2018 ◽

2018 ◽

Vol 11 (11) ◽

pp. 6075-6090 ◽

Cited By ~ 4

Author(s):

Brian J. Butterworth ◽

Brent G. T. Else

Keyword(s):

Carbon Dioxide ◽

Sea Ice ◽

Eddy Covariance ◽

Co2 Flux ◽

Carbon Dioxide Flux ◽

The Arctic ◽

Closed Path ◽

Eddy Covariance Method ◽

Open Path ◽

Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10 m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

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Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

Atmosphere ◽

10.3390/atmos10110666 ◽

2019 ◽

Vol 10 (11) ◽

pp. 666 ◽

Cited By ~ 3

Author(s):

William G. Tsui ◽

Joseph L. Woo ◽

V. Faye McNeill

Keyword(s):

Atmospheric Aerosols ◽

Organic Material ◽

Organic Aerosol ◽

Time Of Day ◽

Aerosol Formation ◽

Atmospheric Models ◽

Cloud Processing ◽

Aerosol Mass ◽

Phase Chemistry ◽

The Impact

Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with coupled gas and aqueous-phase chemistry, to consider the impact of aqueous organic reactions in both aqueous aerosols and clouds on isoprene epoxydiol (IEPOX) SOA over a range of pH for both aqueous phases, including cycling between cloud and aerosol within a single simulation. Low pH aqueous aerosol, in the absence of organic coatings or other morphology which may limit uptake of IEPOX, is found to be an efficient source of IEPOX SOA, consistent with previous work. Cloudwater at pH 4 or lower is also found to be a potentially significant source of IEPOX SOA. This phenomenon is primarily attributed to the relatively high uptake of IEPOX to clouds as a result of higher water content in clouds as compared with aerosol. For more acidic cloudwater, the aqueous organic material is comprised primarily of IEPOX SOA and lower-volatility organic acids. Both cloudwater pH and the time of day or sequence of aerosol-to-cloud or cloud-to-aerosol transitions impacted final aqueous SOA mass and composition in the simulations. The potential significance of cloud processing as a contributor to IEPOX SOA production could account for discrepancies between predicted IEPOX SOA mass from atmospheric models and measured ambient IEPOX SOA mass, or observations of IEPOX SOA in locations where mass transfer limitations are expected in aerosol particles.

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Eddy covariance (EC) fluxes of monoterpene oxidation products from a boreal forest canopy

10.5194/egusphere-egu2020-15188 ◽

2020 ◽

Author(s):

Lejish Vettikkat ◽

Arttu Ylisirniö ◽

Iida Pullinen ◽

Luís Miguel Feijó Barreira ◽

Pasi Miettinen ◽

...

Keyword(s):

Boreal Forest ◽

Eddy Covariance ◽

Organic Compounds ◽

Mass Spectrometer ◽

Time Of Flight ◽

Ground Level ◽

Organic Aerosol ◽

Oxidation Products ◽

Aerosol Formation ◽

Flux Measurements

Oxidation of volatile organic compounds (VOC) by ozone (O3), hydroxyl radicals (OH) and nitrogen oxide radicals (NO3, NOx) reduces their volatility and leads to the formation of secondary organic aerosols (SOA) through gas-particle partitioning. Recent studies have shown that monoterpene (C10H16) oxidation products can participate in all stages of aerosol formation, especially in forested boreal environments. However, deposition of these semi-volatile and (extremely) low-volatility organic compounds (SVOC, LVOC, ELVOC) to surfaces in the canopy directly competes with the gas-particle partitioning and has a substantial effect (~50%) on organic aerosol loading. Hence understanding the fate of these oxidation products is crucial in determining the organic aerosol budget and thereby constraining their contribution to climate-relevant processes such as new-particle formation and cloud formation.Oxidation products of monoterpenes were measured at the station for measuring ecosystem atmosphere relations (SMEAR II), a boreal forest research station in Hyyti&#228;l&#228;, Finland, in spring/summer 2019. The forest is dominated by Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst) which are well known high monoterpene emitters. Eddy covariance (EC) flux measurements of oxygenated organic compounds in the gas phase were performed using an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (I-CIMS) with high frequency (5 Hz) co-located with a sonic anemometer (METEK USA-1) on a tower, 35 m above the forest floor. The ion-molecule reaction (IMR) chamber of I-CIMS was actively humidified to mitigate the dependence of the sensitivity of the measurements on the ambient relative humidity. The EC data were analysed following standard correction procedures like lag correction, coordinate rotation and uncertainty analysis. VOCs and oxygenated VOCs were also measured at ground level using a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus PTR-MS), which is sensitive also to the majority of compounds measured by I-CIMS.We present the first continuous I-CIMS dataset at high time resolution (5 Hz) from a tall tower and calculate the Eddy covariance fluxes of a wide range of monoterpene oxidation products during the primary plant-growth season in a boreal forest. Bidirectional fluxes for formic acid (HCOOH) were observed at a higher temporal resolution than reported in earlier studies. We found an increasing trend in the deposition velocity for heavier monoterpene oxidation products which enables us to constrain the net flow of organics between the atmosphere and the canopy layer using the continuity/mass balance equation. When coupled to ground-based measurements using Vocus-PTR, our EC flux measurements will give further insight about the abundance of organics above the canopy vs near ground-level. We also plan to integrate our observations with a chemical transport model containing details of monoterpene oxidation chemistry (ADCHEM) to simulate the sources and sinks and to derive parameterizations for representing the dry deposition rates of monoterpene oxidation products in the boreal forested environments.

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