The 2nd Aerosol Characterization Experiment (ACE-2): meteorological and
                        chemical context

Verver, Gé; Raes, Frank; Vogelezang, Daan; Johnson, Doug

doi:10.3402/tellusb.v52i2.16089

Cited by 42 publications

(18 citation statements)

References 9 publications

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“…The ACE‐2 study area exhibits typical characteristics of a subtropical oceanic atmosphere in the vicinity of a continent, as discussed by Verver et al (2000). Among these characteristics the most notable is a temperature inversion as consequence of heating by compression of the subsiding air over a relatively cold ocean.…”

Section: Experiment Data and Relevant Instrumentationmentioning

confidence: 98%

Airborne in situ characterization of dry aerosol optical properties in a multisource influenced marine region

Targino¹,

Noone²,

Öström³

2005

Tellus B

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In situ data from the 2nd Aerosol Characterization Experiment (ACE‐2) were used to describe the aerosol optical properties in a marine environment perturbed by continental sources, such as the outflow of European aerosol and dust outbreaks from North Africa. The data consist of airborne measurements made with an integrating nephelometer and absorption photometer. The cases investigated in the ACE‐2 experiment included vertical profiles flown in dusty, polluted and clean airmasses. While it was possible to describe the extensive optical properties (scattering and absorption coefficients) for the clean cases in a more general way, the polluted and dusty cases showed much variability from case to case. The intensive properties (single‐scattering albedo and Ångström exponent) showed little variability with height, in agreement with other studies. A key result in this paper is the strong relationship between single‐scattering albedo and transport time for the polluted cases. Calculations of aerosol optical depth (AOD) made using in situ measurements showed that in the marine‐dominated airmasses the contribution from the free troposphere (FT) to the total columnar AOD is not negligible. In the polluted cases, the marine boundary layer (MBL) dominated the contribution to the total AOD, when this was topped by a clean FT. In the cases when pollution outbreak in the MBL was accompanied by a dusty FT, most of the columnar AOD was due to the dust layer. Assessment of the horizontal variability of the aerosol field, achieved by employing the dry scattering coefficient as proxy data, showed that there was variability in the aerosol concentration at scales below the airmass scale in which the aerosol was embedded. This shows that the concept that the aerosol concentration varies horizontally at the same scale as the airmass can lead to significant errors in the aerosol modelling schemes, in particular on the estimates of the impact of aerosols on the Earth's radiative balance.

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Section: Experiment Data and Relevant Instrumentationmentioning

confidence: 98%

Airborne in situ characterization of dry aerosol optical properties in a multisource influenced marine region

Targino¹,

Noone²,

Öström³

2005

Tellus B

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“…The clean case (denoted as "CLEAN") occurred on 26 June 1997, when the ACE-2 area was under the control of a cyclone that brought in pristine maritime air. The polluted case (denoted as "POLL") occurred on 9 July 1997, when the ACE-2 area was under the influence of the Azores High that brought in anthropogenic pollution from Europe (Verver et al, 2000). For the "CLEAN" and "POLL" cases, the total aerosol number concentrations were 218 cm −3 and 636 cm −3 , respectively (Snider and Brenguier, 2000); and the non sea-salt (nss) sulfate mass concentrations were 0.30 µg m −3 and 2.8 µg m −3 , respectively .…”

Section: Model and Case Descriptionsmentioning

confidence: 99%

Does the threshold representation associated with the autoconversion process matter?

2008

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Abstract. Different ad hoc threshold functions associated with the autoconversion process have been arbitrarily used in atmospheric models. However, it is unclear how these ad hoc functions impact model results. Here systematic investigations of the sensitivities of climatically-important properties: CF (cloud fraction), LWP (liquid water path), and AIE (aerosol indirect effect) to threshold functions have been performed using a 3-D cloud-resolving model. It is found that the effect of threshold representations is larger on instantaneous values than on daily averages; and the effect depends on the percentage of clouds in their transitional stages of converting cloud water to rain water. For both the instantaneous values and daily averages, the sensitivity to the specification of critical radius is more significant than the sensitivity to the "smoothness" of the threshold representation (as embodied in the relative dispersion of droplet size distribution) for drizzling clouds. Moreover, the impact of threshold representations on the AIE is stronger than that on CF and LWP.

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“…The double peak mode suggests that aerosols in this case are a mixture of aerosols from local sources and from other regions (Whitby, 1978;Dal Maso et al, 2007). Because aerosols are aged and oxidized during long-distance transport, these particles are usually composed of secondary organic and inorganic components with more hygroscopicity (Weber et al, 1999;Verver et al, 2000). These aerosols can activate efficiently.…”

Section: Air Mass Influences On Ccn Activity: a Case Studymentioning

confidence: 99%

Impacts of organic aerosols and its oxidation level on CCN activity from measurement at a suburban site in China

Zhang

Sun

et al. 2016

Atmos. Chem. Phys.

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Abstract. This study is concerned with the impacts of organic aerosols on cloud condensation nuclei (CCN) activity based on field measurements made at a suburban site in Northern China. The sensitivity of the estimated CCN number concentration (N CCN ) to both volume fraction of organic material (x org ) and aerosol oxidation level (using f 44 , the fraction of m/z 44 in aerosol organic material) are examined. A strong dependence of CCN number concentration (N CCN ) on the x org and f 44 was noted. The sensitivity of N CCN to volume fraction of organics increased with increasing x org . The impacts of the aerosol particles oxidization or aging level on estimating N CCN were also very significant. When the particles were mostly composed of organics (x org > 60 %), the N CCN at the supersaturation of 0.075 and 0.13 % was underestimated by 46 and 44 %, respectively, if aerosol particles were freshly emitted with primary organics (f 44 < 11 %); the underestimation decreased to 32 and 23 % at the corresponding supersaturations, however, if the particles were with more hygroscopic secondary organics (f 44 > 15 %). The N CCN at the supersaturation of 0.76 % was underestimated by 11 and 4 %, respectively, at f 44 < 11 and f 44 > 15 %. However, for the particles composed of low organics (e.g., x org < 40 %), the effect caused by the f 44 was quite insignificant both at high and low supersaturations. This is because the overall hygroscopicity of the particles is dominated by inorganics such as sulfate and nitrate, which are more hygroscopic than organic compounds. Our results indicated that it would decrease the uncertainties in estimating N CCN and lead to a more accurate estimation of N CCN to increase the proportion of secondary organics, especially when the composition of the aerosols is dominated by organics. The applicability of the CCN activation spectrum obtained at Xinzhou to the Xianghe site, about 400 km to the northeast of Xinzhou, was investigated, with the aim of further examining the sensitivity of N CCN to aerosol type. Overall, the mean CCN efficiency spectrum derived from Xinzhou performs well at Xianghe when the supersaturation levels are > 0.2 % (overestimation of 2-4 %). However, N CCN was overestimated by ∼ 20 % at supersaturation levels of < 0.1 %. This suggests that the overestimation is mainly due to the smaller proportion of aged and oxidized organic aerosols present at Xianghe compared to Xinzhou.

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The 2nd Aerosol Characterization Experiment (ACE-2): meteorological and chemical context

Cited by 42 publications

References 9 publications

Airborne in situ characterization of dry aerosol optical properties in a multisource influenced marine region

Airborne in situ characterization of dry aerosol optical properties in a multisource influenced marine region

Does the threshold representation associated with the autoconversion process matter?

Impacts of organic aerosols and its oxidation level on CCN activity from measurement at a suburban site in China

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