High spatial resolution mapping of aerosol composition and sources in Oakland, California using mobile aerosol mass spectrometry

Abstract. We investigated spatial and temporal patterns in concentration and composition of sub-micron particulate matter (PM1) in Oakland, California in the summer of 2017 using an aerosol mass spectrometer mounted in a mobile laboratory. We performed ∼ 160 hours of mobile sampling in the city over a 20-day period. Measurements are compared for three adjacent neighborhoods with distinct land uses: a central business district (downtown), a residential district (West Oakland), and a major shipping port. The average organic aerosol (OA) concentration is 5.3 μgm−3 and contributes ∼ 50 % of the PM1 mass. OA concentrations in downtown are, on average, 1.5 μgm−3 higher than in West Oakland and Port. We decomposed OA into three factors using positive matrix factorization: hydrocarbon-like OA (HOA; 20 % average contribution), cooking OA (COA; 25 %) and semi-volatile oxidized OA (SV-OOA; 55 %). The collective 45 % contribution from primary OA (HOA + COA) emphasizes the importance of primary emissions in Oakland. The dominant source of primary OA shifts from HOA-rich in the morning to COA-rich after lunch time. COA in downtown is consistently higher than West Oakland and Port due to a large number of restaurants. HOA exhibits variability in space and time. Morning-time HOA concentration in downtown is twice that in Port, but Port HOA increases more than two-fold during mid-day, likely because trucking activity at the Port peaks at that time. Despite the expectation of being spatially uniform, SV-OOA also exhibits spatial differences. Morning-time SV-OOA in downtown is roughly 25 % (∼ 0.6 μgm−3) higher than the rest of Oakland. Even as the entire domain approaches a more uniform photo-chemical state in the afternoon, downtown SV-OOA remains statistically higher than West Oakland and Port, suggesting that downtown is a microenvironment with higher photochemical activity. Higher concentrations of particulate sulfate (also of secondary origin) with no direct sources in Oakland further reflect higher photochemical activity in downtown. A combination of several factors (poor ventilation of air masses in street canyons, higher concentrations of precursor gases, higher concentrations of the hydroxyl radical) likely result in the proposed high photochemical activity in downtown. Lastly, through Van Krevelen analysis of elemental ratios (H/C, O/C) of the OA, we show that OA in Oakland is more chemically reduced than several other urban areas. This underscores the importance of primary emissions in Oakland. We also show that mixing of oceanic air masses with these primary emissions in Oakland is an important processing mechanism that governs the overall OA composition in Oakland. The findings of this study are important because the pollutants we find contributing the most to OA variability, both of primary and secondary origin, are ubiquitous in other urban locations.

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High-spatial-resolution mapping and source apportionment of aerosol composition in Oakland, California, using mobile aerosol mass spectrometry

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-16325-2018 ◽

2018 ◽

Vol 18 (22) ◽

pp. 16325-16344 ◽

Cited By ~ 10

Author(s):

Rishabh U. Shah ◽

Ellis S. Robinson ◽

Peishi Gu ◽

Allen L. Robinson ◽

Joshua S. Apte ◽

...

Keyword(s):

Urban Areas ◽

Gasoline Engine ◽

Central Business District ◽

Photochemical Activity ◽

Spatial And Temporal Patterns ◽

Aerosol Composition ◽

Air Masses ◽

Dominant Source ◽

Aerosol Mass ◽

Primary Emissions

Abstract. We investigated spatial and temporal patterns in the concentration and composition of submicron particulate matter (PM1) in Oakland, California, in the summer of 2017 using an aerosol mass spectrometer mounted in a mobile laboratory. We performed ∼160 h of mobile sampling in the city over a 20-day period. Measurements are compared for three adjacent neighborhoods with distinct land uses: a central business district (“downtown”), a residential district (“West Oakland”), and a major shipping port (“port”). The average organic aerosol (OA) concentration is 5.3 µg m−3 and contributes ∼50 % of the PM1 mass. OA concentrations in downtown are, on average, 1.5 µg m−3 higher than in West Oakland and port. We decomposed OA into three factors using positive matrix factorization: hydrocarbon-like OA (HOA; 20 % average contribution), cooking OA (COA; 25 %), and less-oxidized oxygenated OA (LO-OOA; 55 %). The collective 45 % contribution from primary OA (HOA + COA) emphasizes the importance of primary emissions in Oakland. The dominant source of primary OA shifts from HOA-rich in the morning to COA-rich after lunchtime. COA in downtown is consistently higher than West Oakland and port due to a large number of restaurants. HOA exhibits variability in space and time. The morning-time HOA concentration in downtown is twice that in port, but port HOA increases more than two-fold during midday, likely because trucking activity at the port peaks at that time. While it is challenging to mathematically apportion traffic-emitted OA between drayage trucks and cars, combining measurements of OA with black carbon and CO suggests that while trucks have an important effect on OA and BC at the port, gasoline-engine cars are the dominant source of traffic emissions in the rest of Oakland. Despite the expectation of being spatially uniform, LO-OOA also exhibits spatial differences. Morning-time LO-OOA in downtown is roughly 25 % (∼0.6 µg m−3) higher than the rest of Oakland. Even as the entire domain approaches a more uniform photochemical state in the afternoon, downtown LO-OOA remains statistically higher than West Oakland and port, suggesting that downtown is a microenvironment with higher photochemical activity. Higher concentrations of particulate sulfate (also of secondary origin) with no direct sources in Oakland further reflect higher photochemical activity in downtown. A combination of several factors (poor ventilation of air masses in street canyons, higher concentrations of precursor gases, higher concentrations of the hydroxyl radical) likely results in the proposed high photochemical activity in downtown. Lastly, through Van Krevelen analysis of the elemental ratios (H ∕ C, O ∕ C) of the OA, we show that OA in Oakland is more chemically reduced than several other urban areas. This underscores the importance of primary emissions in Oakland. We also show that mixing of oceanic air masses with these primary emissions in Oakland is an important processing mechanism that governs the overall OA composition in Oakland.

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Characterization and source apportionment of submicron aerosol with aerosol mass spectrometer during the PRIDE-PRD 2006 campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-6911-2011 ◽

2011 ◽

Vol 11 (14) ◽

pp. 6911-6929 ◽

Cited By ~ 52

Author(s):

R. Xiao ◽

N. Takegawa ◽

M. Zheng ◽

Y. Kondo ◽

Y. Miyazaki ◽

...

Keyword(s):

Organic Carbon ◽

Urban Areas ◽

Organic Aerosol ◽

Water Soluble ◽

Aerosol Formation ◽

Aerosol Mass Spectrometer ◽

Air Masses ◽

Submicron Aerosol ◽

Pmf Model ◽

Aerosol Mass

Abstract. Size-resolved chemical compositions of non-refractory submicron aerosol were measured using an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) at the rural site Back Garden (BG), located ~50 km northwest of Guangzhou in July 2006. This paper characterized the submicron aerosol particles of regional air pollution in Pearl River Delta (PRD) in the southern China. Organics and sulfate dominated the submicron aerosol compositions, with average mass concentrations of 11.8 ± 8.4 μg m−3 and 13.5 ± 8.7 μg m−3, respectively. Unlike other air masses, the air masses originated from Southeast-South and passing through the PRD urban areas exhibited distinct bimodal size distribution characteristics for both organics and sulfate: the first mode peaked at vacuum aerodynamic diameters (Dva) ∼200 nm and the second mode occurred at Dva from 300–700 nm. With the information from AMS, it was found from this study that the first mode of organics in PRD regional air masses was contributed by both secondary organic aerosol formation and combustion-related emissions, which is different from most findings in other urban areas (first mode of organics primarily from combustion-related emissions). The analysis of AMS mass spectra data by positive matrix factorization (PMF) model identified three sources of submicron organic aerosol including hydrocarbon-like organic aerosol (HOA), low volatility oxygenated organic aerosol (LV-OOA) and semi-volatile oxygenated organic aerosol (SV-OOA). The strong correlation between HOA and EC indicated primary combustion emissions as the major source of HOA while a close correlation between SV-OOA and semi-volatile secondary species nitrate as well as between LV-OOA and nonvolatile secondary species sulfate suggested secondary aerosol formation as the major source of SV-OOA and LV-OOA at the BG site. However, LV-OOA was more aged than SV-OOA as its spectra was highly correlated with the reference spectra of fulvic acid, an indicator of aged and oxygenated aerosol. The origin of HOA and OOA (the sum of LV-OOA and SV-OOA) has been further confirmed by the statistics that primary organic carbon (POC) and secondary organic carbon (SOC), estimated by the EC tracer method, were closely correlated with HOA and OOA, respectively. The results of the EC tracer method and of the PMF model revealed that primary organic aerosol (POA) constituted ~34–47 % of OA mass and secondary organic aerosol (SOA) constituted ~53–66 % of regional organic aerosol in PRD during summer season. The presence of abundant SOA was consistent with water soluble organic carbon (WSOC) results (accounting for ~60 % of OC on average) by Miyazaki et al. (2009) for the same campaign. OOA correlated well with WSOC at the BG site, indicating that most OOA were water soluble. More specifically, approximately 86 % of LV-OOA and 61 % of SV-OOA were estimated as water soluble species on the basis of carbon content comparison.

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The Importance of Blowing Snow to Antarctic Aerosols: Number Distribution and more than Source-Dependent Composition – results from the 2ODIAC campaign

10.5194/acp-2018-547 ◽

2018 ◽

Author(s):

Michael R. Giordano ◽

Lars E. Kalnajs ◽

J. Douglas Goetz ◽

Anita M. Avery ◽

Erin Katz ◽

...

Keyword(s):

Wind Speed ◽

Ross Sea ◽

Ice Cores ◽

Blowing Snow ◽

Aerosol Composition ◽

Austral Spring ◽

Back Trajectories ◽

Air Masses ◽

Low Wind Speed ◽

Aerosol Mass

Abstract. A fundamental understanding of the processes that control Antarctic aerosols is necessary in determining the aerosol impacts on climate-relevant processes from Antarctic ice cores to clouds. The first in situ observational online composition measurements by an aerosol mass spectrometer (AMS) of Antarctic aerosols were only recently performed during the 2-Season Ozone Depletion and Interaction with Aerosols Campaign (2ODIAC) field campaign. 2ODIAC was deployed to sea ice on the Ross Sea near McMurdo Station over two field seasons: Austral spring-summer 2014 and winter-spring 2015. The results presented here focus on the overall trends in aerosol composition primarily as functions of air masses and local meteorological conditions. The results suggest that air mass back trajectories have little impact on either the absolute or relative concentrations of the aerosol constituents measured by (and inferred from) an AMS at a coastal location. However, when the data is parsed by wind speed, two observations become clear. First, a critical wind speed is required to loft snow from the surface, which, in turn, increases particle counts in all measured size bins. Second, this lofted (blowing) snow significantly increases both aerosol chloride and sodium. Further inspection of the AMS data shows that the increased chloride concentrations have distinctive signatures that differ from chloride measured at low wind speed. Also presented are the Cl:Na ratios of snow samples, aerosol filter samples, and non-chloride aerosol constituents measured by the AMS. Additionally, submicron aerosol iodine and bromine concentrations as functions of wind speed are also presented. The results presented here suggest that aerosol composition in coastal Antarctica is a strong function of wind speed and that the mechanisms determining aerosol composition are likely linked to blowing snow.

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Determination of the biogenic secondary organic aerosol fraction in the boreal forest by NMR spectroscopy

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-941-2012 ◽

2012 ◽

Vol 12 (2) ◽

pp. 941-959 ◽

Cited By ~ 38

Author(s):

E. Finessi ◽

S. Decesari ◽

M. Paglione ◽

L. Giulianelli ◽

C. Carbone ◽

...

Keyword(s):

Nmr Spectroscopy ◽

Boreal Forest ◽

Functional Group ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Spectroscopic Techniques ◽

Aerosol Composition ◽

Air Masses ◽

The North ◽

Aerosol Mass

Abstract. The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements including both filter sampling (PM1) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure on-line concentrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic functional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed separately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrometer organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group compositions. The NMR results supported the AMS speciation of oxidized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organics. The more oxidized component was characterized by a mass spectrum dominated by the m/z 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic backbones highly substituted with oxygenated functional groups (carbonyls/carboxyls and hydroxyls). Such component, contributing on average 50% of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investigations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated with the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral profiles obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources originating biogenic organic aerosols in Hyytiälä by oxidation and condensation mechanisms: reactive terpenes emitted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably exploited to complement aerosol mass spectrometric measurements in organic source apportionment studies.

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Aircraft-based measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-57-2019 ◽

2019 ◽

Vol 19 (1) ◽

pp. 57-76 ◽

Cited By ~ 10

Author(s):

Megan D. Willis ◽

Heiko Bozem ◽

Daniel Kunkel ◽

Alex K. Y. Lee ◽

Hannes Schulz ◽

...

Keyword(s):

Potential Temperature ◽

High Arctic ◽

The Arctic ◽

Chemical Transformations ◽

Aerosol Composition ◽

Air Masses ◽

Aerosol Mass ◽

Arctic Aerosol ◽

Show Evidence ◽

Climate Interactions

Abstract. The sources, chemical transformations and removal mechanisms of aerosol transported to the Arctic are key factors that control Arctic aerosol–climate interactions. Our understanding of sources and processes is limited by a lack of vertically resolved observations in remote Arctic regions. We present vertically resolved observations of trace gases and aerosol composition in High Arctic springtime, made largely north of 80∘ N, during the NETCARE campaign. Trace gas gradients observed on these flights defined the polar dome as north of 66–68∘ 30′ N and below potential temperatures of 283.5–287.5 K. In the polar dome, we observe evidence for vertically varying source regions and chemical processing. These vertical changes in sources and chemistry lead to systematic variation in aerosol composition as a function of potential temperature. We show evidence for sources of aerosol with higher organic aerosol (OA), ammonium and refractory black carbon (rBC) content in the upper polar dome. Based on FLEXPART-ECMWF calculations, air masses sampled at all levels inside the polar dome (i.e., potential temperature <280.5 K, altitude <∼3.5 km) subsided during transport over transport times of at least 10 days. Air masses at the lowest potential temperatures, in the lower polar dome, had spent long periods (>10 days) in the Arctic, while air masses in the upper polar dome had entered the Arctic more recently. Variations in aerosol composition were closely related to transport history. In the lower polar dome, the measured sub-micron aerosol mass was dominated by sulfate (mean 74 %), with lower contributions from rBC (1 %), ammonium (4 %) and OA (20 %). At higher altitudes and higher potential temperatures, OA, ammonium and rBC contributed 42 %, 8 % and 2 % of aerosol mass, respectively. A qualitative indication for the presence of sea salt showed that sodium chloride contributed to sub-micron aerosol in the lower polar dome, but was not detectable in the upper polar dome. Our observations highlight the differences in Arctic aerosol chemistry observed at surface-based sites and the aerosol transported throughout the depth of the Arctic troposphere in spring.

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Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the United Kingdom

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-9037-2011 ◽

2011 ◽

Vol 11 (17) ◽

pp. 9037-9052 ◽

Cited By ~ 68

Author(s):

G. R. McMeeking ◽

W. T. Morgan ◽

M. Flynn ◽

E. J. Highwood ◽

K. Turnbull ◽

...

Keyword(s):

Optical Properties ◽

United Kingdom ◽

Radiative Forcing ◽

Organic Aerosols ◽

Mixing State ◽

Aerosol Composition ◽

Air Masses ◽

The United Kingdom ◽

Aerosol Mass ◽

Urban Plumes

Abstract. Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and hence its climate impact, but few in situ observations of mixing state exist. We present airborne single particle soot photometer (SP2) measurements of refractory BC (rBC) mass concentrations and mixing state coupled with aerosol composition and optical properties measured in urban plumes and regional pollution over the United Kingdom. All data were obtained using instrumentation flown on the UK's BAe-146-301 large Atmospheric Research Aircraft (ARA) operated by the Facility for Airborne Atmospheric Measurements (FAAM). We measured sub-micron aerosol composition using an aerosol mass spectrometer (AMS) and used positive matrix factorization to separate hydrocarbon-like (HOA) and oxygenated organic aerosols (OOA). We found a higher number fraction of thickly coated rBC particles in air masses with large OOA relative to HOA, higher ozone-to-nitrogen oxides (NOx) ratios and large concentrations of total sub-micron aerosol mass relative to rBC mass concentrations. The more ozone- and OOA-rich air masses were associated with transport from continental Europe, while plumes from UK cities had higher HOA and NOx and fewer thickly coated rBC particles. We did not observe any significant change in the rBC mass absorption efficiency calculated from rBC mass and light absorption coefficients measured by a particle soot absorption photometer despite observing significant changes in aerosol composition and rBC mixing state. The contributions of light scattering and absorption to total extinction (quantified by the single scattering albedo; SSA) did change for different air masses, with lower SSA observed in urban plumes compared to regional aerosol (0.85 versus 0.9–0.95). We attribute these differences to the presence of relatively rapidly formed secondary aerosol, primarily OOA and ammonium nitrate, which must be taken into account in radiative forcing calculations.

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Determination of the biogenic secondary organic aerosol fraction in the boreal forest by AMS and NMR measurements

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-22619-2011 ◽

2011 ◽

Vol 11 (8) ◽

pp. 22619-22662 ◽

Cited By ~ 1

Author(s):

E. Finessi ◽

S. Decesari ◽

M. Paglione ◽

L. Giulianelli ◽

C. Carbone ◽

...

Keyword(s):

Boreal Forest ◽

Functional Group ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Spectroscopic Techniques ◽

Aerosol Composition ◽

Air Masses ◽

The North ◽

Aerosol Mass ◽

Fragmentation Patterns

Abstract. The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements including both filter sampling (PM1) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure on-line air mass concentrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic functional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed separately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrometer organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group compositions. The NMR results supported the AMS speciation of oxidized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organics. The more oxidized component was characterized by a mass spectrum dominated by the m/z 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic backbones highly substituted with oxygenated functional groups (carbonyls/carboxyls and hydroxyls). Such component, contributing on average 50 % of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component showed features consistent with less oxygenated aerosols and was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investigations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated to the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral profiles obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources \\mbox{originating} biogenic organic aerosols in Hyytiälä by oxidation and condensation mechanisms: reactive terpenes emitted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably be exploited to complement aerosol mass spectrometric measurements in organic source apportionment studies.

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Atmospheric submicron aerosol composition and particulate organic nitrate formation in a boreal forestland–urban mixed region

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-13483-2014 ◽

2014 ◽

Vol 14 (24) ◽

pp. 13483-13495 ◽

Cited By ~ 24

Author(s):

L. Q. Hao ◽

A. Kortelainen ◽

S. Romakkaniemi ◽

H. Portin ◽

A. Jaatinen ◽

...

Keyword(s):

High Resolution ◽

Organic Aerosol ◽

Organic Nitrate ◽

Organic Nitrates ◽

Aerosol Composition ◽

Aerosol Mass ◽

Secondary Formation ◽

Inorganic Species ◽

Primary Emissions ◽

Urban Emissions

Abstract. The Puijo aerosol–cloud observation station is a unique measurement site for its location in the mixed region between the boreal forestland and the municipality of Kuopio, Finland. A measurement campaign was carried out at the station during fall 2010. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-Tof-AMS) was deployed to characterize the atmospheric submicron aerosols. Positive matrix factorization (PMF) was applied to the unified high-resolution mass spectra organic species with NO+ and NO2+ ions to discover the intrinsic relationships between the organic and inorganic species and their daily cycles. On average, the submicron aerosols in this study were dominated by organic and sulfate species, composing 48.2 and 28.7% of total observed aerosol mass, respectively, with smaller contributions from ammonium (9.3%), nitrate (4.9%), chloride (0.8%) and BC (8.1%). The sources of these species included the primary emissions originating from the city area, secondary formation from both natural and anthropogenic emissions and regional transport. The PMF analysis succeeded in separating the mixed organic and inorganic spectra into three distinct organic and one inorganic factors. For organic factors, the semi-volatile oxygenated organic aerosol (SVOOA) and low-volatility oxygenated OA (LVOOA) accounted for 54.8 and 36.3% of total organic masses, respectively, while the hydrocarbon-like organic aerosol (HOA) accounted for 8.9% of total organics, with its main source from urban emissions. The inorganic factor is identified as NH4NO3, comprising 6.9% of the fitted aerosol mass by PMF. Based on the PMF results, the nitrate species were separated into organic and inorganic components, with the organic nitrates contributing one-third of the total nitrate mass. The results highlight both anthropogenic and biogenic emissions as important atmospheric aerosol sources in a forest–urban mixed region.

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Atmospheric submicron aerosol composition and particulate organic nitrate formation in a boreal forestland–urban mixed region

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-17263-2014 ◽

2014 ◽

Vol 14 (11) ◽

pp. 17263-17298

Author(s):

L. Q. Hao ◽

A. Kortelainen ◽

S. Romakkaniemi ◽

H. Portin ◽

A. Jaatinen ◽

...

Keyword(s):

High Resolution ◽

Organic Aerosol ◽

Organic Nitrate ◽

Organic Nitrates ◽

Aerosol Composition ◽

Aerosol Mass ◽

Secondary Formation ◽

Inorganic Species ◽

Primary Emissions ◽

Urban Emissions

Abstract. The Puijo aerosol-cloud observation station is a~unique measurement site for its location in the mixed region between the boreal forestland and the municipality of Kuopio, Finland. A measurement campaign was carried out at the station during fall 2010. An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-Tof-AMS) was deployed to characterize the atmospheric submicron aerosols. Positive Matrix Factorization (PMF) was applied to the unified high resolution mass spectra organic species with NO+ and NO2+ ions to discover the intrinsic relationships between the organic and inorganic species and their daily cycles. On average, the submicron aerosols in this study were dominated by organic and sulfate species, making 76.9% of total observed aerosol mass, with smaller contributions from ammonium (9.3%), nitrate (4.9%), chloride (0.8%) and BC (8.1%). The sources of these species included the primary emissions originating from the city area, secondary formation from both natural and anthropogenic emissions and regional transport. The PMF analysis succeeded in separating the mixed organic and inorganic spectra into three distinct organic and one inorganic factors. For organic factors, the semi-volatile oxygenated organic aerosol (SVOOA) and low-volatile oxygenated OA (LVOOA) accounted for 89.6% of total organic masses, while the hydrocarbon-like organic aerosol (HOA) consisted of 10.4% of total organics with its main source from urban emissions. The inorganic factor is identified as NH4NO3, comprising 7.5% of the fitted aerosol mass by PMF. Based on the PMF results, the nitrate species were separated into organic and inorganic components, with the organic nitrates contributing 1 / 3 of the total nitrate mass. The results highlight both anthropogenic and biogenic emissions as important atmospheric aerosol sources in a~forest-urban mixed region.

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Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the UK

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-14991-2011 ◽

2011 ◽

Vol 11 (5) ◽

pp. 14991-15027 ◽

Cited By ~ 1

Author(s):

G. R. McMeeking ◽

W. T. Morgan ◽

M. Flynn ◽

E. J. Highwood ◽

K. Turnbull ◽

...

Keyword(s):

Optical Properties ◽

Black Carbon ◽

Radiative Forcing ◽

Organic Aerosols ◽

Mixing State ◽

Aerosol Composition ◽

Air Masses ◽

Aerosol Mass ◽

The Uk ◽

Urban Plumes

Abstract. Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and hence its climate impact, but few in situ observations of mixing state exist. We present airborne single particle soot photometer (SP2) measurements of refractory BC (rBC) mass concentrations and mixing state coupled with aerosol composition and optical properties measured in urban plumes and regional pollution over the UK. All data were obtained using instrumentation flown on the UK's BAe-146-301 large Atmospheric Research Aircraft (ARA) operated by the Facility for Airborne Atmospheric Measurements (FAAM). We measured sub-micron aerosol composition using an aerosol mass spectrometer (AMS) and used positive matrix factorization to separate hydrocarbon-like (HOA) and oxygenated organic aerosols (OOA). We found a higher number fraction of thickly coated rBC particles in air masses with large OOA relative to HOA, higher ozone-to-nitrogen oxides (NOx) ratios and large concentrations of total sub-micron aerosol mass relative to rBC mass concentrations. The more ozone- and OOA-rich air masses were associated with transport from continental Europe, while plumes from UK cities had higher HOA and NOx and fewer thickly coated rBC particles. We did not observe any significant change in the rBC mass absorption efficiency calculated from rBC mass and light absorption coefficients measured by a particle soot absorption photometer despite observing significant changes in aerosol composition and rBC mixing state. The contributions of light scattering and absorption to total extinction (quantified by the single scattering albedo; SSA) did change for different air masses, with lower SSA observed in urban plumes compared to regional aerosol (0.85 versus 0.9–0.95). We attribute these differences to the presence of relatively rapidly formed secondary aerosol, primarily OOA and ammonium nitrate, which must be taken into account in radiative forcing calculations.

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