Aerosol optical properties in the southeastern United States in summer – Part 1: Hygroscopic growth

Abstract. Aircraft observations of meteorological, trace gas, and aerosol properties were made during May–September 2013 in the southeastern United States (US) under fair-weather, afternoon conditions with well-defined planetary boundary layer structure. Optical extinction at 532 nm was directly measured at relative humidities (RHs) of ∼  15, ∼  70, and ∼  90 % and compared with extinction calculated from measurements of aerosol composition and size distribution using the κ-Köhler approximation for hygroscopic growth. The calculated enhancement in hydrated aerosol extinction with relative humidity, f(RH), calculated by this method agreed well with the observed f(RH) at ∼  90 % RH. The dominance of organic aerosol, which comprised 65 ± 10 % of particulate matter with aerodynamic diameter <  1 µm in the planetary boundary layer, resulted in relatively low f(RH) values of 1.43 ± 0.67 at 70 % RH and 2.28 ± 1.05 at 90 % RH. The subsaturated κ-Köhler hygroscopicity parameter κ for the organic fraction of the aerosol must have been <  0.10 to be consistent with 75 % of the observations within uncertainties, with a best estimate of κ  =  0.05. This subsaturated κ value for the organic aerosol in the southeastern US is broadly consistent with field studies in rural environments. A new, physically based, single-parameter representation was developed that better described f(RH) than did the widely used gamma power-law approximation.

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Aerosol optical properties in the southeastern United States in summer – Part 1: Hygroscopic growth

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-25695-2015 ◽

2015 ◽

Vol 15 (18) ◽

pp. 25695-25738 ◽

Cited By ~ 4

Author(s):

C. A. Brock ◽

N. L. Wagner ◽

B. E. Anderson ◽

A. R. Attwood ◽

A. Beyersdorf ◽

...

Keyword(s):

United States ◽

Layer Structure ◽

Southeastern United States ◽

Field Studies ◽

Hygroscopic Growth ◽

Particle Volume ◽

Aerosol Composition ◽

Optical Extinction ◽

Airborne Measurements ◽

Southeastern Us

Abstract. Aircraft observations of meteorological, trace gas, and aerosol properties were made during May–September 2013 in the southeastern United States (US) under fair-weather, afternoon conditions with well-defined planetary boundary layer structure. Optical extinction at 532 nm was directly measured at three relative humidities and compared with extinction calculated from measurements of aerosol composition and size distribution using the κ-Köhler approximation for hygroscopic growth. Using this approach, the hygroscopicity parameter κ for the organic fraction of the aerosol must have been < 0.10 to be consistent with 75 % of the observations within uncertainties. This subsaturated κ value for the organic aerosol in the southeastern US is consistent with several field studies in rural environments. We present a new parameterization of the change in aerosol extinction as a function of relative humidity that better describes the observations than does the widely used power-law (gamma, γ) parameterization. This new single-parameter κext formulation is based upon κ-Köhler and Mie theories and relies upon the well-known approximately linear relationship between particle volume (or mass) and optical extinction (Charlson et al., 1967). The fitted parameter, κext, is nonlinearly related to the chemically derived κ parameter used in κ-Köhler theory. The values of κext we determined from airborne measurements are consistent with independent observations at a nearby ground site.

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Effects of anthropogenic emissions on aerosol formation from isoprene and monoterpenes in the southeastern United States

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1417609112 ◽

2014 ◽

Vol 112 (1) ◽

pp. 37-42 ◽

Cited By ~ 306

Author(s):

Lu Xu ◽

Hongyu Guo ◽

Christopher M. Boyd ◽

Mitchel Klein ◽

Aikaterini Bougiatioti ◽

...

Keyword(s):

United States ◽

Particulate Matter ◽

Fine Particulate Matter ◽

Southeastern United States ◽

Organic Aerosol ◽

High Time Resolution ◽

Organic Nitrates ◽

Aerosol Formation ◽

Radical Oxidation ◽

Southeastern Us

Secondary organic aerosol (SOA) constitutes a substantial fraction of fine particulate matter and has important impacts on climate and human health. The extent to which human activities alter SOA formation from biogenic emissions in the atmosphere is largely undetermined. Here, we present direct observational evidence on the magnitude of anthropogenic influence on biogenic SOA formation based on comprehensive ambient measurements in the southeastern United States (US). Multiple high-time-resolution mass spectrometry organic aerosol measurements were made during different seasons at various locations, including urban and rural sites in the greater Atlanta area and Centreville in rural Alabama. Our results provide a quantitative understanding of the roles of anthropogenic SO2 and NOx in ambient SOA formation. We show that isoprene-derived SOA is directly mediated by the abundance of sulfate, instead of the particle water content and/or particle acidity as suggested by prior laboratory studies. Anthropogenic NOx is shown to enhance nighttime SOA formation via nitrate radical oxidation of monoterpenes, resulting in the formation of condensable organic nitrates. Together, anthropogenic sulfate and NOx can mediate 43–70% of total measured organic aerosol (29–49% of submicron particulate matter, PM1) in the southeastern US during summer. These measurements imply that future reduction in SO2 and NOx emissions can considerably reduce the SOA burden in the southeastern US. Updating current modeling frameworks with these observational constraints will also lead to more accurate treatment of aerosol formation for regions with substantial anthropogenic−biogenic interactions and consequently improve air quality and climate simulations.

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Vertical profiling of aerosol hygroscopic properties in the planetary boundary layer during the PEGASOS campaigns

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-7295-2016 ◽

2016 ◽

Vol 16 (11) ◽

pp. 7295-7315 ◽

Cited By ~ 7

Author(s):

Bernadette Rosati ◽

Martin Gysel ◽

Florian Rubach ◽

Thomas F. Mentel ◽

Brigitta Goger ◽

...

Keyword(s):

Boundary Layer ◽

Chemical Composition ◽

The Netherlands ◽

Planetary Boundary Layer ◽

Aerosol Particles ◽

Time Of Day ◽

Hygroscopic Growth ◽

Aerosol Composition ◽

Hygroscopic Properties ◽

Direct Measurements

Abstract. Vertical profiles of the aerosol particles hygroscopic properties, their mixing state as well as chemical composition were measured above northern Italy and the Netherlands. An aerosol mass spectrometer (AMS; for chemical composition) and a white-light humidified optical particle spectrometer (WHOPS; for hygroscopic growth) were deployed on a Zeppelin NT airship within the PEGASOS project. This allowed one to investigate the development of the different layers within the planetary boundary layer (PBL), providing a unique in situ data set for airborne aerosol particles properties in the first kilometre of the atmosphere. Profiles measured during the morning hours on 20 June 2012 in the Po Valley, Italy, showed an increased nitrate fraction at ∼  100 m above ground level (a.g.l.) coupled with enhanced hygroscopic growth compared to ∼  700 m a. g. l. This result was derived from both measurements of the aerosol composition and direct measurements of the hygroscopicity, yielding hygroscopicity parameters (κ) of 0.34  ± 0.12 and 0.19  ± 0.07 for 500 nm particles, at ∼  100 and ∼  700 m a. g. l., respectively. The difference is attributed to the structure of the PBL at this time of day which featured several independent sub-layers with different types of aerosols. Later in the day the vertical structures disappeared due to the mixing of the layers and similar aerosol particle properties were found at all probed altitudes (mean κ ≈ 0.18  ± 0.07). The aerosol properties observed at the lowest flight level (100 m a. g. l.) were consistent with parallel measurements at a ground site, both in the morning and afternoon. Overall, the aerosol particles were found to be externally mixed, with a prevailing hygroscopic fraction. The flights near Cabauw in the Netherlands in the fully mixed PBL did not feature altitude-dependent characteristics. Particles were also externally mixed and had an even larger hygroscopic fraction compared to the results in Italy. The mean κ from direct measurements was 0.28 ± 0.10, thus considerably higher than κ values measured in Italy in the fully mixed PBL.

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In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC<sup>4</sup>RS: observations of a modest aerosol enhancement aloft

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7085-2015 ◽

2015 ◽

Vol 15 (12) ◽

pp. 7085-7102 ◽

Cited By ~ 40

Author(s):

N. L. Wagner ◽

C. A. Brock ◽

W. M. Angevine ◽

A. Beyersdorf ◽

P. Campuzano-Jost ◽

...

Keyword(s):

United States ◽

Mixed Layer ◽

Transition Layer ◽

Southeastern United States ◽

Vertical Mixing ◽

Organic Aerosol ◽

Vertical Profiles ◽

Free Troposphere ◽

Secondary Aerosol

Abstract. Vertical profiles of submicron aerosol from in situ aircraft-based measurements were used to construct aggregate profiles of chemical, microphysical, and optical properties. These vertical profiles were collected over the southeastern United States (SEUS) during the summer of 2013 as part of two separate field studies: the Southeast Nexus (SENEX) study and the Study of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS). Shallow cumulus convection was observed during many profiles. These conditions enhance vertical transport of trace gases and aerosol and create a cloudy transition layer on top of the sub-cloud mixed layer. The trace gas and aerosol concentrations in the transition layer were modeled as a mixture with contributions from the mixed layer below and the free troposphere above. The amount of vertical mixing, or entrainment of air from the free troposphere, was quantified using the observed mixing ratio of carbon monoxide (CO). Although the median aerosol mass, extinction, and volume decreased with altitude in the transition layer, they were ~10 % larger than expected from vertical mixing alone. This enhancement was likely due to secondary aerosol formation in the transition layer. Although the transition layer enhancements of the particulate sulfate and organic aerosol (OA) were both similar in magnitude, only the enhancement of sulfate was statistically significant. The column integrated extinction, or aerosol optical depth (AOD), was calculated for each individual profile, and the transition layer enhancement of extinction typically contributed less than 10 % to the total AOD. Our measurements and analysis were motivated by two recent studies that have hypothesized an enhanced layer of secondary aerosol aloft to explain the summertime enhancement of AOD (2–3 times greater than winter) over the southeastern United States. The first study attributes the layer aloft to secondary organic aerosol (SOA) while the second study speculates that the layer aloft could be SOA or secondary particulate sulfate. In contrast to these hypotheses, the modest enhancement we observed in the transition layer was not dominated by OA and was not a large fraction of the summertime AOD.

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Vertical Distribution of Particulate Matter and its Relationship with Planetary Boundary Layer Structure in Shenyang, Northeast China

Aerosol and Air Quality Research ◽

10.4209/aaqr.2019.06.0311 ◽

2019 ◽

Vol 19 (11) ◽

pp. 2464-2476 ◽

Cited By ~ 3

Author(s):

Xiaolan Li ◽

Yanjun Ma ◽

Yangfeng Wang ◽

Wei Wei ◽

Yunhai Zhang ◽

...

Keyword(s):

Boundary Layer ◽

Particulate Matter ◽

Vertical Distribution ◽

Planetary Boundary Layer ◽

Northeast China ◽

Layer Structure ◽

Boundary Layer Structure

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Public entrepreneurs and the adoption of broad-based merit aid beyond the Southeastern United States

Education Policy Analysis Archives ◽

10.14507/epaa.v21n58.2013 ◽

2013 ◽

Vol 21 ◽

pp. 58

Author(s):

William Kyle Ingle ◽

Ruth Ann Petroff

Keyword(s):

United States ◽

Diffusion Theory ◽

Full Range ◽

Southeastern United States ◽

Merit Aid ◽

Theoretical Frameworks ◽

Southeastern Us ◽

Public Colleges And Universities ◽

Aid Programs ◽

K 12

The concentration of broad-based merit aid adoption in the southeastern United States has been well noted in the literature. However, there are states that have adopted broad-based merit aid programs outside of the Southeast. Guided by multiple theoretical frameworks, including innovation diffusion theory (e.g., Gray, 1973, 1994; Rogers, 2003), Roberts and King’s (1991) typology of public entrepreneurs, and Anderson’s (2003) stages of the policymaking process, this qualitative study sought to answer the following questions. First, in the absence of regional diffusion pressures, what internal determinants are reported as accounting for the diffusion of broad-based merit aid programs outside of the Southeastern US? What types of public entrepreneurs were identified as playing key roles in establishing merit aid in states outside the southeastern US? During which stages of the policymaking process were they active? We found that merit aid was a means of addressing an array of public problems, including low college going rates at in-state public colleges and universities, and weak K-12 accountability. Consistent factors reported as facilitating merit aid creation included a strong, vocal public advocate (governors and a university system president) and a desire to strengthen state economies and diversify workforces. A full range of public entrepreneurs played key roles in developing merit aid in the sampled states. Political and executive entrepreneurs were in the forefront of merit aid efforts, but our data suggest that a cast of supporting public entrepreneurs were integral to the eventual adoption of broad-based merit aid in the sampled states.

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