Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: results from DISCOVER-AQ California

Abstract. The San Joaquin Valley (SJV) in California experiences persistent air quality problems associated with elevated particulate matter (PM) concentrations due to anthropogenic emissions, topography, and meteorological conditions. Thus it is important to unravel the various sources and processes that affect the physico-chemical properties of PM in order to better inform pollution abatement strategies and improve parameterizations in air quality models. During January and February 2013, a ground supersite was installed at the Fresno-Garland California Air Resources Board (CARB) monitoring station, where comprehensive, real-time measurements of PM and trace gases were performed using instruments including an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and an Ionicon Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-TOF-MS) as part of the NASA Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. The average submicron aerosol (PM1) concentration was 31.0 μg m−3 and the total mass was dominated by organic aerosols (OA, 55 %), followed by ammonium nitrate (35 %). High PM pollution events were commonly associated with elevated OA concentrations, mostly from primary sources. Organic aerosols had average atomic oxygen-to-carbon (O / C), hydrogen-to-carbon (H / C), and nitrogen-to-carbon (N / C) ratios of 0.42, 1.70, and 0.017, respectively. Six distinct sources of organic aerosol were identified from positive matrix factorization (PMF) analysis of the AMS data: hydrocarbon-like OA (HOA; 9 % of total OA; O / C = 0.09) associated with local traffic, cooking OA (COA; 28 % of total OA; O / C = 0.19) associated with food cooking activities, two biomass burning OAs (BBOA1; 13 % of total OA; O / C = 0.33 and BBOA2; 20 % of total OA; O / C = 0.60) most likely associated with residential space heating from wood combustion, and semi-volatile oxygenated OA (SV-OOA; 16 % of total OA; O / C = 0.63) and low volatility oxygenated OA (LV-OOA; 24 % of total OA; O / C = 0.90) formed via chemical reactions in the atmosphere. Large differences in aerosol chemistry at Fresno were observed between the current campaign (winter 2013) and a previous wintertime campaign (winter 2010), most notably that PM1 concentrations were nearly three times higher in 2013 than in 2010. These variations were attributed to differences in the meteorological conditions, which influenced primary emissions and secondary aerosol formation. In particular, COA and BBOA concentrations were greater in 2013 than 2010, where colder temperatures in 2013 likely resulted in increased biomass burning activities. The influence from a nighttime formed residual layer that mixed down in the morning was found to be much more intense in 2013 than 2010, leading to sharp increases in ground-level concentrations of secondary aerosol species including nitrate, sulfate, and OOA, in the morning between 08:00 to 12:00 PST. This is an indication that nighttime chemistry might also be higher in 2013. As solar radiation was stronger in 2013 the higher nitrate and OOA concentrations in 2013 could also be partly due to greater photochemical production of secondary aerosol species. The greater solar radiation and larger range in temperature in 2013 also likely led to both SV-OOA and LV-OOA being observed in 2013 whereas only a single OOA factor was identified in 2010.

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Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: results from DISCOVER-AQ California

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-5427-2016 ◽

2016 ◽

Vol 16 (8) ◽

pp. 5427-5451 ◽

Cited By ~ 36

Author(s):

Dominique E. Young ◽

Hwajin Kim ◽

Caroline Parworth ◽

Shan Zhou ◽

Xiaolu Zhang ◽

...

Keyword(s):

Air Quality ◽

Solar Radiation ◽

Mass Spectrometer ◽

Chemical Reactions ◽

Biomass Burning ◽

Time Of Flight ◽

Organic Aerosols ◽

Meteorological Conditions ◽

Aerosol Chemistry ◽

Secondary Aerosol

Abstract. The San Joaquin Valley (SJV) in California experiences persistent air-quality problems associated with elevated particulate matter (PM) concentrations due to anthropogenic emissions, topography, and meteorological conditions. Thus it is important to unravel the various sources and processes that affect the physicochemical properties of PM in order to better inform pollution abatement strategies and improve parameterizations in air-quality models. During January and February 2013, a ground supersite was installed at the Fresno–Garland California Air Resources Board (CARB) monitoring station, where comprehensive, real-time measurements of PM and trace gases were performed using instruments including an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and an Ionicon proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) as part of the NASA Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. The average submicron aerosol (PM1) concentration was 31.0 µg m−3 and the total mass was dominated by organic aerosols (OA, 55 %), followed by ammonium nitrate (35 %). High PM pollution events were commonly associated with elevated OA concentrations, mostly from primary sources. Organic aerosols had average atomic oxygen-to-carbon (O / C), hydrogen-to-carbon (H / C), and nitrogen-to-carbon (N / C) ratios of 0.42, 1.70, and 0.017, respectively. Six distinct sources of organic aerosol were identified from positive matrix factorization (PMF) analysis of the AMS data: hydrocarbon-like OA (HOA; 9 % of total OA, O / C  =  0.09) associated with local traffic, cooking OA (COA; 18 % of total OA, O / C  =  0.19) associated with food cooking activities, two biomass burning OA (BBOA1: 13 % of total OA, O / C  =  0.33; BBOA2: 20 % of total OA, O / C  =  0.60) most likely associated with residential space heating from wood combustion, and semivolatile oxygenated OA (SV-OOA; 16 % of total OA, O / C  =  0.63) and low-volatility oxygenated OA (LV-OOA; 24 % of total OA, O / C  =  0.90) formed via chemical reactions in the atmosphere. Large differences in aerosol chemistry at Fresno were observed between the current campaign (winter 2013) and a previous campaign in winter 2010, most notably that PM1 concentrations were nearly 3 times higher in 2013 than in 2010. These variations were attributed to differences in the meteorological conditions, which influenced primary emissions and secondary aerosol formation. In particular, COA and BBOA concentrations were greater in 2013 than 2010, where colder temperatures in 2013 likely resulted in increased biomass burning activities. The influence from a nighttime formed residual layer that mixed down in the morning was found to be much more intense in 2013 than 2010, leading to sharp increases in ground-level concentrations of secondary aerosol species including nitrate, sulfate, and OOA, in the morning between 08:00 and 12:00 PST. This is an indication that nighttime chemical reactions may have played a more important role in 2013. As solar radiation was stronger in 2013 the higher nitrate and OOA concentrations in 2013 could also be partly due to greater photochemical production of secondary aerosol species. The greater solar radiation and larger range in temperature in 2013 also likely led to both SV-OOA and LV-OOA being observed in 2013 whereas only a single OOA factor was identified in 2010.

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Sources and mixing state of size-resolved elemental carbon particles in a European megacity: Paris

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-1681-2012 ◽

2012 ◽

Vol 12 (4) ◽

pp. 1681-1700 ◽

Cited By ~ 111

Author(s):

R. M. Healy ◽

J. Sciare ◽

L. Poulain ◽

K. Kamili ◽

M. Merkel ◽

...

Keyword(s):

Mass Spectrometer ◽

Biomass Burning ◽

Single Particle ◽

Mass Concentration ◽

Elemental Carbon ◽

Fossil Fuel ◽

Time Of Flight ◽

Particle Mass ◽

Mass Size ◽

Mass Concentrations

Abstract. An Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS) was deployed to investigate the size-resolved chemical composition of single particles at an urban background site in Paris, France, as part of the MEGAPOLI winter campaign in January/February 2010. ATOFMS particle counts were scaled to match coincident Twin Differential Mobility Particle Sizer (TDMPS) data in order to generate hourly size-resolved mass concentrations for the single particle classes observed. The total scaled ATOFMS particle mass concentration in the size range 150–1067 nm was found to agree very well with the sum of concurrent High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and Multi-Angle Absorption Photometer (MAAP) mass concentration measurements of organic carbon (OC), inorganic ions and black carbon (BC) (R2 = 0.91). Clustering analysis of the ATOFMS single particle mass spectra allowed the separation of elemental carbon (EC) particles into four classes: (i) EC attributed to biomass burning (ECbiomass), (ii) EC attributed to traffic (ECtraffic), (iii) EC internally mixed with OC and ammonium sulfate (ECOCSOx), and (iv) EC internally mixed with OC and ammonium nitrate (ECOCNOx). Average hourly mass concentrations for EC-containing particles detected by the ATOFMS were found to agree reasonably well with semi-continuous quantitative thermal/optical EC and optical BC measurements (r2 = 0.61 and 0.65–0.68 respectively, n = 552). The EC particle mass assigned to fossil fuel and biomass burning sources also agreed reasonably well with BC mass fractions assigned to the same sources using seven-wavelength aethalometer data (r2 = 0.60 and 0.48, respectively, n = 568). Agreement between the ATOFMS and other instrumentation improved noticeably when a period influenced by significantly aged, internally mixed EC particles was removed from the intercomparison. 88% and 12% of EC particle mass was apportioned to fossil fuel and biomass burning respectively using the ATOFMS data compared with 85% and 15% respectively for BC estimated from the aethalometer model. On average, the mass size distribution for EC particles is bimodal; the smaller mode is attributed to locally emitted, mostly externally mixed EC particles, while the larger mode is dominated by aged, internally mixed ECOCNOx particles associated with continental transport events. Periods of continental influence were identified using the Lagrangian Particle Dispersion Model (LPDM) "FLEXPART". A consistent minimum between the two EC mass size modes was observed at approximately 400 nm for the measurement period. EC particles below this size are attributed to local emissions using chemical mixing state information and contribute 79% of the scaled ATOFMS EC particle mass, while particles above this size are attributed to continental transport events and contribute 21% of the EC particle mass. These results clearly demonstrate the potential benefit of monitoring size-resolved mass concentrations for the separation of local and continental EC emissions. Knowledge of the relative input of these emissions is essential for assessing the effectiveness of local abatement strategies.

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Measurements and Comparative Air Quality Analysis of a Goat Farm Operation

Transactions of the ASABE ◽

10.13031/trans.13344 ◽

2019 ◽

Vol 62 (6) ◽

pp. 1723-1733

Author(s):

Arndreya Howard ◽

Venkata S. V. Botlaguduru ◽

Hongbo Du ◽

Raghava R. Kommalapati ◽

Ziaul Huque

Keyword(s):

Hydrogen Sulfide ◽

Air Quality ◽

Solar Radiation ◽

Multiple Regression ◽

Air Pollutants ◽

Emission Rate ◽

Particle Diameter ◽

Ambient Air ◽

Meteorological Conditions ◽

Goat Farm

Abstract. Air pollutants such as hydrogen sulfide, ammonia, particulate matter (PM10 and PM2.5), methane, and volatile organic compounds (VOCs) are harmful to the respiratory systems of humans and animals. Livestock facilities have been documented as a major source of dangerous air pollutants; however, there is a lack of data on the emissions from goat farms. This study investigated a goat farm in Texas to evaluate the emission levels and determine the correlation of meteorological conditions with these pollutants. Two locations on the goat farm were selected for monitoring: inside a goat barn, and at a manure lagoon. The monitoring campaign was conducted over a 53-day period during winter and summer seasons. Carbon dioxide, ozone, nitrous oxide, ammonia, PM10, PM2.5, hydrogen sulfide, methane, and VOCs were measured to determine hourly average concentrations using chemiluminescent instruments. An analysis of meteorological conditions using multiple regression was conducted to investigate probable correlations between emission rates and characteristic climate data, such as temperature, humidity, barometric pressure, and solar radiation. Particle size distributions of PM10 and PM2.5 were evaluated for the two monitoring locations during the different seasons to determine the typical particle diameter and the impact of season on particle diameter. The highest emission rate of 364.4 ±50 g m-2 d-1 occurred at the manure lagoon for methane, which contributed the most to the overall emissions at this animal operation. The regression results for the manure lagoon had the highest positive correlations for ozone with temperature and solar radiation. The outdoor meteorological conditions had the most significant influence on pollutants at both locations. Therefore, meteorological conditions are instrumental in the intensity of the air pollutants found on animal farms. The particle diameters ranged from 0.1 to 6.0 µm in the goat barn and from 0.3 to 1.0 µm at the manure lagoon. Even though moderate levels of emissions were monitored at this facility, the emissions from the goat farm do not pose a risk to human health and do not significantly impact the ambient air quality when compared to other livestock facilities.HighlightsEmissions from a goat farm were measured inside a goat barn and at a manure lagoon over summer and winter seasons.The highest methane emission rate of 364.4 ±50 g m-2 d-1 occurred at the manure lagoon during summer.Meteorological conditions significantly influenced emissions at both locations, especially for O3 at the manure lagoon.Emissions from goat farm operations are much lower than those from cow, swine, and chicken farm operations. Keywords: Air quality, Ammonia, Emissions, Goat farm, Methane, Multiple regression analysis.

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Sources of organic aerosols in Europe: a modeling study using CAMx with modified volatility basis set scheme

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-15247-2019 ◽

2019 ◽

Vol 19 (24) ◽

pp. 15247-15270 ◽

Cited By ~ 3

Author(s):

Jianhui Jiang ◽

Sebnem Aksoyoglu ◽

Imad El-Haddad ◽

Giancarlo Ciarelli ◽

Hugo A. C. Denier van der Gon ◽

...

Keyword(s):

Air Quality ◽

Source Apportionment ◽

Biomass Burning ◽

Agricultural Waste ◽

Organic Aerosols ◽

Basis Set ◽

Anthropogenic Sources ◽

Wood Burning ◽

Gasoline Vehicles

Abstract. Source apportionment of organic aerosols (OAs) is of great importance to better understand the health impact and climate effects of particulate matter air pollution. Air quality models are used as potential tools to identify OA components and sources at high spatial and temporal resolution; however, they generally underestimate OA concentrations, and comparisons of their outputs with an extended set of measurements are still rare due to the lack of long-term experimental data. In this study, we addressed such challenges at the European level. Using the regional Comprehensive Air Quality Model with Extensions (CAMx) and a volatility basis set (VBS) scheme which was optimized based on recent chamber experiments with wood burning and diesel vehicle emissions, and which contains more source-specific sets compared to previous studies, we calculated the contribution of OA components and defined their sources over a whole-year period (2011). We modeled separately the primary and secondary OA contributions from old and new diesel and gasoline vehicles, biomass burning (mostly residential wood burning and agricultural waste burning excluding wildfires), other anthropogenic sources (mainly shipping, industry and energy production) and biogenic sources. An important feature of this study is that we evaluated the model results with measurements over a longer period than in previous studies, which strengthens our confidence in our modeled source apportionment results. Comparison against positive matrix factorization (PMF) analyses of aerosol mass spectrometric measurements at nine European sites suggested that the modified VBS scheme improved the model performance for total OA as well as the OA components, including hydrocarbon-like (HOA), biomass burning (BBOA) and oxygenated components (OOA). By using the modified VBS scheme, the mean bias of OOA was reduced from −1.3 to −0.4 µg m−3 corresponding to a reduction of mean fractional bias from −45 % to −20 %. The winter OOA simulation, which was largely underestimated in previous studies, was improved by 29 % to 42 % among the evaluated sites compared to the default parameterization. Wood burning was the dominant OA source in winter (61 %), while biogenic emissions contributed ∼ 55 % to OA during summer in Europe on average. In both seasons, other anthropogenic sources comprised the second largest component (9 % in winter and 19 % in summer as domain average), while the average contributions of diesel and gasoline vehicles were rather small (∼ 5 %) except for the metropolitan areas where the highest contribution reached 31 %. The results indicate the need to improve the emission inventory to include currently missing and highly uncertain local emissions, as well as further improvement of VBS parameterization for winter biomass burning. Although this study focused on Europe, it can be applied in any other part of the globe. This study highlights the ability of long-term measurements and source apportionment modeling to validate and improve emission inventories, and identify sources not yet properly included in existing inventories.

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Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) – Part 2: Biomass burning influences in winter

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-8037-2019 ◽

2019 ◽

Vol 19 (12) ◽

pp. 8037-8062 ◽

Cited By ~ 15

Author(s):

Lu Qi ◽

Mindong Chen ◽

Giulia Stefenelli ◽

Veronika Pospisilova ◽

Yandong Tong ◽

...

Keyword(s):

Electrospray Ionization ◽

Source Apportionment ◽

Mass Spectrometer ◽

Biomass Burning ◽

Time Of Flight ◽

Organic Aerosol ◽

Climate Impacts ◽

Ionization Time ◽

Flight Mass Spectrometer ◽

Tof Ms

Abstract. Real-time, in situ molecular composition measurements of the organic fraction of fine particulate matter (PM2.5) remain challenging, hindering a full understanding of the climate impacts and health effects of PM2.5. In particular, the thermal decomposition and ionization-induced fragmentation affecting current techniques has limited a detailed investigation of secondary organic aerosol (SOA), which typically dominates OA. Here we deploy a novel extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) during winter 2017 in downtown Zurich, Switzerland, which overcomes these limitations, together with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and supporting instrumentation. Positive matrix factorization (PMF) implemented within the Multilinear Engine (ME-2) program was applied to the EESI-TOF-MS data to quantify the primary and secondary contributions to OA. An 11-factor solution was selected as the best representation of the data, including five primary and six secondary factors. Primary factors showed influence from cooking, cigarette smoke, biomass burning (two factors) and a special local unknown event occurred only during two nights. Secondary factors were affected by biomass burning (three factors, distinguished by temperature and/or wind direction), organonitrates, monoterpene oxidation, and undetermined regional processing, in particular the contributions of wood combustion. While the AMS attributed slightly over half the OA mass to SOA but did not identify its source, the EESI-TOF-MS showed that most (>70 %) of the SOA was derived from biomass burning. Together with significant contributions from less aged biomass burning factors identified by both AMS and EESI-TOF-MS, this firmly establishes biomass burning as the single most important contributor to OA mass at this site during winter. High correlation was obtained between EESI-TOF-MS and AMS PMF factors where specific analogues existed, as well as between total signal and POA–SOA apportionment. This suggests the EESI-TOF-MS apportionment in the current study can be approximately taken at face value, despite ion-by-ion differences in relative sensitivity. The apportionment of specific ions measured by the EESI-TOF-MS (e.g., levoglucosan, nitrocatechol, and selected organic acids) and utilization of a cluster analysis-based approach to identify key marker ions for the EESI-TOF-MS factors are investigated. The interpretability of the EESI-TOF-MS results and improved source separation relative to the AMS within this pilot campaign validate the EESI-TOF-MS as a promising approach to source apportionment and atmospheric composition research.

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Secondary organic aerosol formation from smoldering and flaming combustion of biomass: a box model parametrization based on volatility basis set

10.5194/acp-2018-1308 ◽

2019 ◽

Cited By ~ 2

Author(s):

Giulia Stefenelli ◽

Jianhui Jiang ◽

Amelie Bertrand ◽

Emily A. Bruns ◽

Simone M. Pieber ◽

...

Keyword(s):

Mass Spectrometer ◽

Secondary Organic Aerosol ◽

Time Of Flight ◽

Organic Aerosol ◽

Box Model ◽

Basis Set ◽

Model Parameters ◽

Oh Radicals ◽

Smog Chamber ◽

Aerosol Formation

Abstract. Box model simulations based on the volatility basis set (VBS) approach were used to assess secondary organic aerosol (SOA) precursors and volatility distributions from residential wood combustion. Emissions were sampled from three different residential stoves at different combustion conditions (flaming vs. smoldering-dominated), aging temperatures (−10 °C, 2 °C and 15 °C), and emission loads, then exposed to hydroxyl (OH) radicals in a smog chamber. Primary emissions of SOA precursor compounds, organic aerosol and their evolution during aging in the smog chamber were monitored by a comprehensive suite of gas and particle instrumentation, including a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). SOA precursors were classified according to their chemical composition and the identification of the nature of the precursors revealed useful to better constrain model parameters, in particular SOA production rates and molecular characteristics of the condensable gases formed. The general aim of the model was the determination of the parameters describing the volatility distributions of the oxidation products from the different chemical classes considered and their temperature dependence. Novel parameterization methods based on a genetic algorithm (GA) approach allowed estimation of precursor class contributions to SOA and evaluation of the effect of emission variability on SOA yield predictions. Significant differences were observed in the gas-phase composition between smoldering and flaming emissions. Smoldering phase emissions were dominated by oxidized VOCs with less than six carbon atoms family (OVOCc

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Impacts of the Denver Cyclone on regional air quality and aerosol formation in the Colorado Front Range during FRAPPÉ 2014

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-12039-2016 ◽

2016 ◽

Vol 16 (18) ◽

pp. 12039-12058 ◽

Cited By ~ 14

Author(s):

Kennedy T. Vu ◽

Justin H. Dingle ◽

Roya Bahreini ◽

Patrick J. Reddy ◽

Eric C. Apel ◽

...

Keyword(s):

Air Quality ◽

Metropolitan Area ◽

Chemical Constituents ◽

Organic Aerosols ◽

Front Range ◽

Aerosol Formation ◽

Optical Extinction ◽

Airborne Measurements ◽

Regional Air Quality ◽

Mass Concentrations

Abstract. We present airborne measurements made during the 2014 Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ) project to investigate the impacts of the Denver Cyclone on regional air quality in the greater Denver area. Data on trace gases, non-refractory submicron aerosol chemical constituents, and aerosol optical extinction (βext) at λ  =  632 nm were evaluated in the presence and absence of the surface mesoscale circulation in three distinct study regions of the Front Range: In-Flow, Northern Front Range, and the Denver metropolitan area. Pronounced increases in mass concentrations of organics, nitrate, and sulfate in the Northern Front Range and the Denver metropolitan area were observed during the cyclone episodes (27–28 July) compared to the non-cyclonic days (26 July, 2–3 August). Organic aerosols dominated the mass concentrations on all evaluated days, with a 45 % increase in organics on cyclone days across all three regions, while the increase during the cyclone episode was up to ∼  80 % over the Denver metropolitan area. In the most aged air masses (NOx / NOy  <  0.5), background organic aerosols over the Denver metropolitan area increased by a factor of ∼  2.5 due to transport from Northern Front Range. Furthermore, enhanced partitioning of nitric acid to the aerosol phase was observed during the cyclone episodes, mainly due to increased abundance of gas phase ammonia. During the non-cyclone events, βext displayed strong correlations (r  =  0.71) with organic and nitrate in the Northern Front Range and only with organics (r  =  0.70) in the Denver metropolitan area, while correlation of βext during the cyclone was strongest (r  =  0.86) with nitrate over Denver. Mass extinction efficiency (MEE) values in the Denver metropolitan area were similar on cyclone and non-cyclone days despite the dominant influence of different aerosol species on βext. Our analysis showed that the meteorological patterns associated with the Denver Cyclone increased aerosol mass loadings in the Denver metropolitan area mainly by transporting aerosols and/or aerosol precursors from the northern regions, leading to impaired visibility and air quality deterioration.

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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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Secondary organic aerosol formation and primary organic aerosol oxidation from biomass-burning smoke in a flow reactor during FLAME-3

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-11551-2013 ◽

2013 ◽

Vol 13 (22) ◽

pp. 11551-11571 ◽

Cited By ~ 162

Author(s):

A. M. Ortega ◽

D. A. Day ◽

M. J. Cubison ◽

W. H. Brune ◽

D. Bon ◽

...

Keyword(s):

Mass Spectrometer ◽

Biomass Burning ◽

Flow Reactor ◽

Organic Aerosol ◽

Proton Transfer Reaction ◽

Oxidation Products ◽

Chemical Transformations ◽

Aerosol Formation ◽

Aerosol Mass ◽

Smog Chambers

Abstract. We report the physical and chemical effects of photochemically aging dilute biomass-burning smoke. A "potential aerosol mass" (PAM) flow reactor was used with analysis by a high-resolution aerosol mass spectrometer and a proton-transfer-reaction ion-trap mass spectrometer during the FLAME-3 campaign. Hydroxyl (OH) radical concentrations in the reactor reached up to ~1000 times average tropospheric levels, producing effective OH exposures equivalent to up to 5 days of aging in the atmosphere, and allowing for us to extend the investigation of smoke aging beyond the oxidation levels achieved in traditional smog chambers. Volatile organic compound (VOC) observations show aromatics and terpenes decrease with aging, while formic acid and other unidentified oxidation products increase. Unidentified gas-phase oxidation products, previously observed in atmospheric and laboratory measurements, were observed here, including evidence of multiple generations of photochemistry. Substantial new organic aerosol (OA) mass ("net SOA"; secondary OA) was observed from aging biomass-burning smoke, resulting in total OA average of 1.42 ± 0.36 times the initial primary OA (POA) after oxidation. This study confirms that the net-SOA-to-POA ratio of biomass-burning smoke is far lower on average than that observed for urban emissions. Although most fuels were very reproducible, significant differences were observed among the biomasses, with some fuels resulting in a doubling of the OA mass, while for others a very small increase or even a decrease was observed. Net SOA formation in the photochemical reactor increased with OH exposure (OHexp), typically peaking around three days of equivalent atmospheric photochemical age (OHexp~3.9 × 1011 molecules cm−3 s), then leveling off at higher exposures. The amount of additional OA mass added from aging is positively correlated with initial POA concentration, but not with the total VOC concentration or the concentration of known SOA precursors. The mass of SOA formed often exceeded the mass of the known VOC precursors, indicating the likely importance of primary semivolatile/intermediate volatility species, and possibly of unidentified VOCs as SOA precursors in biomass burning smoke. Chemical transformations continued even after mass concentration stabilized. Changes in the biomass-burning tracer f60 ranged from substantially decreasing to remaining constant with increased aging. With increased OHexp, oxidation was always detected (as indicated by f44 and O/C). POA O/C ranged from 0.15 to 0.5, while aged OA O/C reached up to 0.87. The rate of oxidation and maximum O/C achieved differs for each biomass, and appears to increase with the initial O/C of the POA.

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