bluuebunny/crossref_metadata_2025 huggingface dataset:
Teaching Introductory Life Science Courses in Colleges of Agriculture: Faculty Experiences
Authors: Balschweid Mark , Knobloch Neil A. , Hains Bryan J.
Published: January 2016

Insignificant numbers of college students declaring STEM majors creates concern for the future of the U.S. economy within the global marketplace. This study highlights the educational development and teaching strategies employed by STEM faculty in teaching first-year students in contextualized life science courses, such as animal, plant, and food sciences. Teaching strategies employed by faculty were reported as largely influenced by the “way they were taught.” Faculty members shared they used ‘lecture’ and ‘laboratory’ interchangeably as both educational environment and instructional practice. This study provides evidence for engaging university teaching faculty in a systematic process of professional development in teaching and learning processes.
Enhancing the Capacity to Create Behavior Change: Extension Key Leaders’ Opinions about Social Marketing and Evaluation
Authors: Warner Laura A.
Published: January 2016

Extension educators endeavor to create and measure outcomes beyond knowledge gain. The purpose of this qualitative study was to explore the role of social marketing as a method for creating behavior change within the University of Florida Extension system through key leader opinions. Additionally, the study sought to identify perceptions about program evaluation and training needs related to this area. Semi-structured interviews were conducted with key leaders at the local, regional, and state levels within Florida Extension. Overall, the participants saw great potential in applying social marketing to Extension programming, and identified knowledge, resources, and terminology as key barriers to Extension agents’ adoption of this approach. In discussing program evaluation related to behavior change, the key leaders expressed strong interest in the creation of standardized evaluation tools and the provision of professional development training to support social marketing and evaluation competencies. The interviews revealed substantial confusion between the terms social marketing and social media. A recommendation is made to revisit the term social marketing within Extension, and for educators to consider alternate terminology to eliminate confusion. Implications of the study point to the development of training opportunities that empower Extension professionals to encourage and evaluate behavior change. It is suggested that Extension professionals are already employing many elements of social marketing. Finally, a blending of the Conceptual Programming model with the social marketing process is discussed as a means of structuring Extension program planning when using social marketing.
Improving aerosol interaction with clouds and precipitation in a regional chemical weather modeling system
Authors: Zhou C. , Zhang X. , Gong S. , Wang Y. , Xue M.
Published: January 2016

Abstract. A comprehensive aerosol–cloud–precipitation interaction (ACI) scheme has been developed under a China Meteorological Administration (CMA) chemical weather modeling system, GRAPES/CUACE (Global/Regional Assimilation and PrEdiction System, CMA Unified Atmospheric Chemistry Environment). Calculated by a sectional aerosol activation scheme based on the information of size and mass from CUACE and the thermal-dynamic and humid states from the weather model GRAPES at each time step, the cloud condensation nuclei (CCN) are interactively fed online into a two-moment cloud scheme (WRF Double-Moment 6-class scheme – WDM6) and a convective parameterization to drive cloud physics and precipitation formation processes. The modeling system has been applied to study the ACI for January 2013 when several persistent haze-fog events and eight precipitation events occurred.The results show that aerosols that interact with the WDM6 in GRAPES/CUACE obviously increase the total cloud water, liquid water content, and cloud droplet number concentrations, while decreasing the mean diameters of cloud droplets with varying magnitudes of the changes in each case and region. These interactive microphysical properties of clouds improve the calculation of their collection growth rates in some regions and hence the precipitation rate and distributions in the model, showing 24 to 48 % enhancements of threat score for 6 h precipitation in almost all regions. The aerosols that interact with the WDM6 also reduce the regional mean bias of temperature by 3 °C during certain precipitation events, but the monthly means bias is only reduced by about 0.3 °C.
Can we explain the observed methane variability after the Mount Pinatubo eruption?
Authors: Bândă N. , Krol M. , van Weele M. , van Noije T. , Le Sager P. , Röckmann T.
Published: January 2016

Abstract. The CH4 growth rate in the atmosphere showed large variations after the Pinatubo eruption in June 1991. A decrease of more than 10 ppb yr−1 in the growth rate over the course of 1992 was reported, and a partial recovery in the following year. Although several reasons have been proposed to explain the evolution of CH4 after the eruption, their contributions to the observed variations are not yet resolved. CH4 is removed from the atmosphere by the reaction with tropospheric OH, which in turn is produced by O3 photolysis under UV radiation. The CH4 removal after the Pinatubo eruption might have been affected by changes in tropospheric UV levels due to the presence of stratospheric SO2 and sulfate aerosols, and due to enhanced ozone depletion on Pinatubo aerosols. The perturbed climate after the eruption also altered both sources and sinks of atmospheric CH4. Furthermore, CH4 concentrations were influenced by other factors of natural variability in that period, such as El Niño–Southern Oscillation (ENSO) and biomass burning events. Emissions of CO, NOX and non-methane volatile organic compounds (NMVOCs) also affected CH4 concentrations indirectly by influencing tropospheric OH levels.Potential drivers of CH4 variability are investigated using the TM5 global chemistry model. The contribution that each driver had to the global CH4 variability during the period 1990 to 1995 is quantified. We find that a decrease of 8–10 ppb yr−1 CH4 is explained by a combination of the above processes. However, the timing of the minimum growth rate is found 6&nash;9 months later than observed. The long-term decrease in CH4 growth rate over the period 1990 to 1995 is well captured and can be attributed to an increase in OH concentrations over this time period. Potential uncertainties in our modelled CH4 growth rate include emissions of CH4 from wetlands, biomass burning emissions of CH4 and other compounds, biogenic NMVOC and the sensitivity of OH to NMVOC emission changes. Two inventories are used for CH4 emissions from wetlands, ORCHIDEE and LPJ, to investigate the role of uncertainties in these emissions. Although the higher climate sensitivity of ORCHIDEE improves the simulated CH4 growth rate change after Pinatubo, none of the two inventories properly captures the observed CH4 variability in this period.
Hygroscopicity of nanoparticles produced from homogeneous nucleation in the CLOUD experiments
Authors: Kim J. , Ahlm L. , Yli-Juuti T. , Lawler M. , Keskinen H. , Tröstl J. , Schobesberger S. , Duplissy J. , Amorim A. , Bianchi F. , Donahue N. M. , Flagan R. C. , Hakala J. , Heinritzi M. , Jokinen T. , Kürten A. , Laaksonen A. , Lehtipalo K. , Miettinen P. , Petäjä T. , Rissanen M. P. , Rondo L. , Sengupta K. , Simon M. , Tomé A. , Williamson C. , Wimmer D. , Winkler P. M. , Ehrhart S. , Ye P. , Kirkby J. , Curtius J. , Baltensperger U. , Kulmala M. , Lehtinen K. E. J. , Smith J. N. , Riipinen I. , Virtanen A.
Published: January 2016

Abstract. Sulfuric acid, amines and oxidized organics have been found to be important compounds in the nucleation and initial growth of atmospheric particles. Because of the challenges involved in determining the chemical composition of objects with very small mass, however, the properties of the freshly nucleated particles and the detailed pathways of their formation processes are still not clear. In this study, we focus on a challenging size range, i.e., particles that have grown to diameters of 10 and 15 nm following nucleation, and measure their water uptake. Water uptake is useful information for indirectly obtaining chemical composition of aerosol particles. We use a nanometer-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) at subsaturated conditions (ca. 90 % relative humidity at 293 K) to measure the hygroscopicity of particles during the seventh Cosmics Leaving OUtdoor Droplets (CLOUD7) campaign performed at CERN in 2012. In CLOUD7, the hygroscopicity of nucleated nanoparticles was measured in the presence of sulfuric acid, sulfuric acid–dimethylamine, and sulfuric acid–organics derived from α-pinene oxidation. The hygroscopicity parameter κ decreased with increasing particle size, indicating decreasing acidity of particles. No clear effect of the sulfuric acid concentration on the hygroscopicity of 10 nm particles produced from sulfuric acid and dimethylamine was observed, whereas the hygroscopicity of 15 nm particles sharply decreased with decreasing sulfuric acid concentrations. In particular, when the concentration of sulfuric acid was 5.1 × 106 molecules cm−3 in the gas phase, and the dimethylamine mixing ratio was 11.8 ppt, the measured κ of 15 nm particles was 0.31 ± 0.01: close to the value reported for dimethylaminium sulfate (DMAS) (κDMAS ∼ 0.28). Furthermore, the difference in κ between sulfuric acid and sulfuric acid–imethylamine experiments increased with increasing particle size. The κ values of particles in the presence of sulfuric acid and organics were much smaller than those of particles in the presence of sulfuric acid and dimethylamine. This suggests that the organics produced from α-pinene ozonolysis play a significant role in particle growth even at 10 nm sizes.
Nitrogen speciation in various types of aerosols in spring over the northwestern Pacific Ocean
Authors: Luo L. , Yao X. H. , Gao H. W. , Hsu S. C. , Li J. W. , Kao S. J.
Published: January 2016

Abstract. The cumulative atmospheric nitrogen deposition has been found to profoundly impact the nutrient stoichiometry of the eastern China seas (ECSs: the Yellow Sea and East China Sea) and the northwestern Pacific Ocean (NWPO). In spite of the potential significance of dry deposition in those regions, shipboard observations of atmospheric aerosols remain insufficient, particularly regarding the compositions of water-soluble nitrogen species (nitrate, ammonium and water-soluble organic nitrogen – WSON). We conducted a cruise covering the ECSs and the NWPO during the spring of 2014 and observed three types of atmospheric aerosols. Aluminum content, air mass backward trajectories, weather conditions, and ion stoichiometry allowed us to discern dust aerosol patches and sea-fog-modified aerosols (widespread over the ECSs) from background aerosols (open ocean). Among the three types, sea-fog-modified aerosols contained the highest concentrations of nitrate (536 ± 300 nmol N m−3), ammonium (442 ± 194 nmol N m−3) and WSON (147 ± 171 nmol N m−3); furthermore, ammonium and nitrate together occupied  ∼  65 % of the molar fraction of total ions. The dust aerosols also contained significant amounts of nitrate (100 ± 23 nmol N m−3) and ammonium (138 ± 24 nmol N m−3) which were obviously larger than those in the background aerosols (26 ± 32 for nitrate and 54 ± 45 nmol N m−3 for ammonium), yet this was not the case for WSON. It appeared that dust aerosols had less of a chance to come in contact with WSON during their transport. In the open ocean, we found that sea salt (e.g., Na+, Cl−, Mg2+), as well as WSON, correlated positively with wind speed. Apparently, marine dissolved organic nitrogen (DON) was emitted from breaking waves. Regardless of the variable wind speeds from 0.8 to as high as 18 m s−1, nitrate and ammonium, by contrast, remained in narrow ranges, implying that some supply and consumption processes of nitrate and ammonium were required to maintain such a quasi-static condition. Mean dry deposition of total dissolved nitrogen (TDN) for sea-fog-modified aerosols (1090 ± 671 µmol N m−2 d−1) was 5 times higher than that for dust aerosols (190 ± 41.6 µmol N m−2 d−1) and around 20 times higher than that for background aerosols (56.8 ± 59.1 µmol N m−2 d−1). Apparently, spring sea fog on the ECSs played an important role in removing atmospheric reactive nitrogen from the Chinese mainland and depositing it into the ECSs, thus effectively preventing its seaward export to the NWPO.
Evaluating the skill of high-resolution WRF-Chem simulations in describing drivers of aerosol direct climate forcing on the regional scale
Authors: Crippa P. , Sullivan R. C. , Thota A. , Pryor S. C.
Published: January 2016

Abstract. Assessing the ability of global and regional models to describe aerosol optical properties is essential to reducing uncertainty in aerosol direct radiative forcing in the contemporary climate and to improving confidence in future projections. Here we evaluate the performance of high-resolution simulations conducted using the Weather Research and Forecasting model with coupled with Chemistry (WRF-Chem) in capturing spatiotemporal variability of aerosol optical depth (AOD) and the Ångström exponent (AE) by comparison with ground- and space-based remotely sensed observations. WRF-Chem is run over eastern North America at a resolution of 12 km for a representative year (2008). A systematic positive bias in simulated AOD relative to observations is found (annual mean fractional bias (MFB) is 0.15 and 0.50 relative to MODIS (MODerate resolution Imaging Spectroradiometer) and AERONET, respectively), whereas the spatial variability is well captured during most months. The spatial correlation of observed and simulated AOD shows a clear seasonal cycle with highest correlation during summer months (r = 0.5–0.7) when the aerosol loading is large and more observations are available. The model is biased towards the simulation of coarse-mode aerosols (annual MFB for AE  =  −0.10 relative to MODIS and −0.59 for AERONET), but the spatial correlation for AE with observations is 0.3–0.5 during most months, despite the fact that AE is retrieved with higher uncertainty from the remote-sensing observations. WRF-Chem also exhibits high skill in identifying areas of extreme and non-extreme aerosol loading, and its ability to correctly simulate the location and relative intensity of extreme aerosol events (i.e., AOD  >  75th percentile) varies between 30 and 70 % during winter and summer months, respectively.
Fog composition at Baengnyeong Island in the eastern Yellow Sea: detecting markers of aqueous atmospheric oxidations
Authors: Boris A. J. , Lee T. , Park T. , Choi J. , Seo S. J. , Collett Jr. J. L.
Published: January 2016

Abstract. Samples of fog water were collected at Baengnyeong Island (BYI) in the Yellow Sea during the summer of 2014. The most abundant chemical species in the fog water were NH4+ (mean of 2220 µM), NO3− (1260 µM), SO4−2 (730 µM), and Na+ (551 µM), with substantial contributions from other species consistent with marine and biomass burning influence on some dates. The pH of the samples ranged between 3.48 and 5.00, with a mean of 3.94, intermediate within pH values of fog/cloud water reported previously in Southeast Asia. Back trajectories (72 h) showed that high relative humidity ( >  80 %) was encountered upwind of the sampling site by all but one of the sampled air masses, and that the fog composition at BYI can be impacted by several different source regions, including the Sea of Japan, southeastern China, northeastern China, and the East China Sea. Sulfur in the collected fog was highly oxidized: low S(IV) concentrations were measured (mean of 2.36 µM) in contrast to SO4−2 and in contrast to fog/cloud S(IV) concentrations from pollutant source regions; organosulfate species were also observed and were most likely formed through aging of mainly biogenic volatile organic compounds. Low-molecular-mass organic acids were major contributors to total organic carbon (TOC; 36–69 %), comprising a fraction of TOC at the upper end of that seen in fogs and clouds in other polluted environments. Large contributions were observed from not only acetic and formic acids but also oxalic, succinic, maleic, and other organic acids that can be produced in aqueous atmospheric organic processing (AAOP) reactions. These samples of East Asian fog water containing highly oxidized components represent fog downwind of pollutant sources and can provide new insight into the fate of regional emissions. In particular, these samples demonstrate the result of extensive photochemical aging during multiday transport, including oxidation within wet aerosols and fogs.
Possible influence of atmospheric circulations on winter haze pollution in the Beijing–Tianjin–Hebei region, northern China
Authors: Zhang Z. , Zhang X. , Gong D. , Kim S.-J. , Mao R. , Zhao X.
Published: January 2016

Abstract. Using the daily records derived from the synoptic weather stations and the NCEP/NCAR and ERA-Interim reanalysis data, the variability of the winter haze pollution (indicated by the mean visibility and number of hazy days) in the Beijing–Tianjin–Hebei (BTH) region during the period 1981 to 2015 and its relationship with the atmospheric circulations at middle–high latitude were analyzed in this study. The winter haze pollution in BTH had distinct inter-annual and inter-decadal variabilities without a significant long-term trend. According to the spatial distribution of correlation coefficients, six atmospheric circulation indices (I1 to I6) were defined from the key areas in sea level pressure (SLP), zonal and meridional winds at 850 hPa (U850, V850), geopotential height field at 500 hPa (H500), zonal wind at 200 hPa (U200), and air temperature at 200 hPa (T200), respectively. All of the six indices have significant and stable correlations with the winter visibility and number of hazy days in BTH. In the raw (unfiltered) correlations, the correlation coefficients between the six indices and the winter visibility (number of hazy days) varied from 0.57 (0.47) to 0.76 (0.6) with an average of 0.65 (0.54); in the high-frequency ( < 10 years) correlations, the coefficients varied from 0.62 (0.58) to 0.8 (0.69) with an average of 0.69 (0.64). The six circulation indices together can explain 77.7 % (78.7 %) and 61.7 % (69.1 %) variances of the winter visibility and the number of hazy days in the year-to-year (inter-annual) variability, respectively. The increase in Ic (a comprehensive index derived from the six individual circulation indices) can cause a shallowing of the East Asian trough at the middle troposphere and a weakening of the Siberian high-pressure field at sea level, and is then accompanied by a reduction (increase) of horizontal advection and vertical convection (relative humidity) in the lowest troposphere and a reduced boundary layer height in BTH and its neighboring areas, which are favorable for the formation of haze pollution in BTH winter, and vice versa. The high level of the prediction statistics and the reasonable mechanism suggested that the winter haze pollution in BTH can be forecasted or estimated credibly based on the optimized atmospheric circulation indices. Thus it is helpful for government decision-making departments to take action in advance in dealing with probably severe haze pollution in BTH indicated by the atmospheric circulation conditions.
A sub-decadal trend in diacids in atmospheric aerosols in eastern Asia
Authors: Kundu S. , Kawamura K. , Kobayashi M. , Tachibana E. , Lee M. , Fu P. Q. , Jung J.
Published: January 2016

Abstract. Change in secondary organic aerosols (SOAs) has been predicted to be highly uncertain in the future atmosphere in Asia. To better quantify the SOA change, we examine the sub-decadal (2001–2008) trend in major surrogate compounds (C2–C10 diacids) of SOA in atmospheric aerosols from Gosan site on Cheju Island, South Korea. The Gosan site is influenced by pollution outflows from eastern Asia. The molecular distributions of diacids were characterized by the predominance of oxalic (C2) acid followed by malonic (C3) and succinic (C4) acids in each year. The seasonal variations in diacids in each year were characterized by the highest concentrations of saturated diacids in spring and unsaturated diacids in winter. The consistent molecular distributions and seasonal variations along with significantly similar air mass transport patterns are indicative of similar pollution sources for diacids in eastern Asia on a sub-decadal scale. However, the intensity of the pollution sources has increased as evidenced by the increases in major diacids at the rate of 3.9–47.4 % per year, particularly in April. The temporal variations in atmospheric tracer compounds (carbon monoxide, levoglucosan, 2-methyltetrols, pinic acid, glyoxylic acid, glyoxal and methylglyoxal) suggest that the increases in diacids are due to enhanced precursor emissions associated with more anthropogenic than biogenic activities followed by the compounds' chemical processing in the atmosphere. The trends in diacids contrast with the reported decreases in sulfate, nitrate and ammonium in recent years in eastern Asia. This study demonstrates that recent pollution control strategies in eastern Asia were not able to decrease organic acidic species in the atmosphere. The increases in water-soluble organic acid fraction could modify the aerosol organic composition and its sensitivity to climate relevant physical properties.
Fine particulate matter in the tropical environment: monsoonal effects, source apportionment, and health risk assessment
Authors: Khan M. F. , Latif M. T. , Saw W. H. , Amil N. , Nadzir M. S. M. , Sahani M. , Tahir N. M. , Chung J. X.
Published: January 2016

Abstract. The health implications of PM2.5 in the tropical region of Southeast Asia (SEA) are significant as PM2.5 can pose serious health concerns. PM2.5 concentration and sources here are strongly influenced by changes in the monsoon regime from the south-west quadrant to the north-east quadrant in the region. In this work, PM2.5 samples were collected at a semi-urban area using a high-volume air sampler at different seasons on 24 h basis. Analysis of trace elements and water-soluble ions was performed using inductively coupled plasma mass spectroscopy (ICP-MS) and ion chromatography (IC), respectively. Apportionment analysis of PM2.5 was carried out using the United States Environmental Protection Agency (US EPA) positive matrix factorization (PMF) 5.0 and a mass closure model. We quantitatively characterized the health risks posed to human populations through the inhalation of selected heavy metals in PM2.5. 48 % of the samples collected exceeded the World Health Organization (WHO) 24 h PM2.5 guideline but only 19 % of the samples exceeded 24 h US EPA National Ambient Air Quality Standard (NAAQS). The PM2.5 concentration was slightly higher during the north-east monsoon compared to south-west monsoon. The main trace metals identified were As, Pb, Cd, Ni, Mn, V, and Cr while the main ions were SO42−, NO3−, NH4+, and Na. The mass closure model identified four major sources of PM2.5 that account for 55 % of total mass balance. The four sources are mineral matter (MIN) (35 %), secondary inorganic aerosol (SIA) (11 %), sea salt (SS) (7 %), and trace elements (TE) (2 %). PMF 5.0 elucidated five potential sources: motor vehicle emissions coupled with biomass burning (31 %) were the most dominant, followed by marine/sulfate aerosol (20 %), coal burning (19 %), nitrate aerosol (17 %), and mineral/road dust (13 %). The hazard quotient (HQ) for four selected metals (Pb, As, Cd, and Ni) in PM2.5 mass was highest in PM2.5 mass from the coal burning source and least in PM2.5 mass originating from the mineral/road dust source. The main carcinogenic heavy metal of concern to health at the current location was As; the other heavy metals (Ni, Pb, and Cd) did not pose a significant cancer risk in PM2.5 mass concentration. Overall, the associated lifetime cancer risk posed by the exposure of hazardous metals in PM2.5 is 3–4 per 1 000 000 people at this location.
Formation of secondary aerosols from gasoline vehicle exhaust when mixing with SO2
Authors: Liu T. , Wang X. , Hu Q. , Deng W. , Zhang Y. , Ding X. , Fu X. , Bernard F. , Zhang Z. , Lü S. , He Q. , Bi X. , Chen J. , Sun Y. , Yu J. , Peng P. , Sheng G. , Fu J.
Published: January 2016

Abstract. Sulfur dioxide (SO2) can enhance the formation of secondary aerosols from biogenic volatile organic compounds (VOCs), but its influence on secondary aerosol formation from anthropogenic VOCs, particularly complex mixtures like vehicle exhaust, remains uncertain. Gasoline vehicle exhaust (GVE) and SO2, a typical pollutant from coal burning, are directly co-introduced into a smog chamber, in this study, to investigate the formation of secondary organic aerosols (SOA) and sulfate aerosols through photooxidation. New particle formation was enhanced, while substantial sulfate was formed through the oxidation of SO2 in the presence of high concentration of SO2. Homogenous oxidation by OH radicals contributed a negligible fraction to the conversion of SO2 to sulfate, and instead the oxidation by stabilized Criegee intermediates (sCIs), formed from alkenes in the exhaust reacting with ozone, dominated the conversion of SO2. After 5 h of photochemical aging, GVE's SOA production factor revealed an increase by 60–200 % in the presence of high concentration of SO2. The increase could principally be attributed to acid-catalyzed SOA formation as evidenced by the strong positive linear correlation (R2 = 0.97) between the SOA production factor and in situ particle acidity calculated by the AIM-II model. A high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) resolved OA's relatively lower oxygen-to-carbon (O : C) (0.44 ± 0.02) and higher hydrogen-to-carbon (H : C) (1.40 ± 0.03) molar ratios for the GVE / SO2 mixture, with a significantly lower estimated average carbon oxidation state (OSc) of −0.51 ± 0.06 than −0.19 ± 0.08 for GVE alone. The relative higher mass loading of OA in the experiments with SO2 might be a significant explanation for the lower SOA oxidation degree.
The impact of shipping emissions on air pollution in the greater North Sea region – Part 2: Scenarios for 2030
Authors: Matthias V. , Aulinger A. , Backes A. , Bieser J. , Geyer B. , Quante M. , Zeretzke M.
Published: January 2016

Abstract. Scenarios for future shipping emissions in the North Sea have been developed in the framework of the Clean North Sea Shipping project. The effects of changing NOx and SO2 emissions were investigated with the CMAQ chemistry transport model for the year 2030 in the North Sea area. It has been found that, compared to today, the contribution of shipping to the NO2 and O3 concentrations will increase due to the expected enhanced traffic by more than 20 and 5 %, respectively, by 2030 if no regulation for further emission reductions is implemented in the North Sea area. PM2.5 will decrease slightly because the sulfur contents in ship fuels will be reduced as international regulations foresee. The effects differ largely between regions, seasons and date of the implementation of stricter regulations for NOx emissions from newly built ships.
Observations of cloud microphysics and ice formation during COPE
Authors: Taylor J. W. , Choularton T. W. , Blyth A. M. , Liu Z. , Bower K. N. , Crosier J. , Gallagher M. W. , Williams P. I. , Dorsey J. R. , Flynn M. J. , Bennett L. J. , Huang Y. , French J. , Korolev A. , Brown P. R. A.
Published: January 2016

Abstract. We present microphysical observations of cumulus clouds measured over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) in August 2013, which are framed into a wider context using ground-based and airborne radar measurements. Two lines of cumulus clouds formed in the early afternoon along convergence lines aligned with the peninsula. The lines became longer and broader during the afternoon due to new cell formation and stratiform regions forming downwind of the convective cells. Ice concentrations up to 350 L−1, well in excess of the expected ice nuclei (IN) concentrations, were measured in the mature stratiform regions, suggesting that secondary ice production was active. Detailed sampling focused on an isolated liquid cloud that glaciated as it matured to merge with a band of cloud downwind. In the initial cell, drizzle concentrations increased from  ∼ 0.5 to  ∼ 20 L−1 in around 20 min. Ice concentrations developed up to a few per litre, which is around the level expected of primary IN. The ice images were most consistent with freezing drizzle, rather than smaller cloud drops or interstitial IN forming the first ice. As new cells emerged in and around the cloud, ice concentrations up to 2 orders of magnitude higher than the predicted IN concentrations developed, and the cloud glaciated over a period of 12–15 min. Almost all of the first ice particles to be observed were frozen drops, while vapour-grown ice crystals were dominant in the latter stages. Our observations are consistent with the production of large numbers of small secondary ice crystals/fragments, by a mechanism such as Hallett–Mossop or droplets shattering upon freezing. Some of the small ice froze drizzle drops on contact, while others grew more slowly by vapour deposition. Graupel and columns were seen in cloud penetrations up to the −12 °C level, though many ice particles were mixed habit due to riming and growth by vapour deposition at multiple temperatures. Our observations demonstrate that the freezing of drizzle/raindrops is an important process that dominates the formation of large ice in the intermediate stages of cloud development. As these frozen drops were the first precipitation observed, interactions between the warm-rain and secondary ice production processes appear to be key to determining the timing and location of precipitation.
The Rate of Equilibration of Viscous Aerosol Particles
Authors: O'Meara S. , Topping D.O , McFiggans G.
Published: January 2016

Abstract. The proximity of atmospheric aerosol particles to equilibrium with their surrounding condensable vapours can substantially impact their transformations, fate and impacts and is the subject of vibrant research activity. In this study we first compare equilibration timescales estimated by three different models for diffusion through aerosol particles to assess any sensitivity to choice of model framework. Equilibration times for diffusion coefficients with varying dependencies on composition are compared for the first time. We show that even under large changes in the saturation ratio of a semi-volatile component (es) of 1-90% predicted equilibration timescales are in agreement, including when diffusion coefficients vary with composition. For condensing water and a diffusion coefficient dependent on composition, a plasticising effect is observed, leading to a decreased estimated equilibration time with increasing final es. Above 60% final es maximum equilibration times of around 1 s are estimated for comparatively large particles (10 µm) containing a relatively low diffusivity component (1x1025 m2s−1 in pure form). This, as well as other results here, questions whether particle-phase diffusion can be a limiting factor in gas-particle mass transfer in the ambient atmosphere, at least for water-soluble particles. In the second part of this study, we explore sensitivities associated with the use of particle radius measurements to infer diffusion coefficient dependencies on composition using a diffusion model. Given quantified similarities between models used in this study, our results confirm considerations that must be taken into account when designing such experiments. Although quantitative agreement of equilibration timescales between models is found, further work is necessary to determine their suitability for assessing atmospheric impacts, such as their inclusion in polydisperse aerosol simulations.
Long-resident droplets at the stratocumulus top
Authors: de Lozar Alberto , Muessle Lukas
Published: January 2016

Abstract. Turbulence models predict low droplet-collision rates in stratocumulus clouds, which should imply a narrow droplet-size distribution and little rain. Contrary to this expectation, rain is often observed in stratocumulus. In this paper we explore the hypothesis that some droplets can grow well above the average, because small-scale turbulence allows them to reside at cloud top for a time longer than the convective-eddy time t*. Long-resident droplets can grow larger because condensation due to long-wave radiative cooling and collisions have more time to enhance droplet growth. We investigate the trajectories of one billion Lagrangian droplets in direct numerical simulations of a cloudy mixed-layer configuration that is based on observations from the flight 11 from the VERDI campaign. High resolution is employed to represent a well-developed turbulent state at cloud top. Only one-way coupling is considered. We observe that 70% of the droplets spend less than 0.6t* at cloud top before leaving the cloud, while 15% of the droplets remain at least 0.9t* at cloud top. Besides, 0.2% of the droplets spend more than 2.5t* at cloud top and decouple from the large-scale convective eddies that brought them to the top, with the result that they become memoryless. Modeling collisions like a Poisson process leads to the conclusion that most rain droplets originate from those memoryless droplets. Furthermore, most long-resident droplets accumulate at the downdraft regions of the flow, which could be related to the closed-cell stratocumulus pattern. Finally, we see that condensation due to long-wave radiative cooling considerably broadens the cloud-top droplet-size distribution: 6.5% of the droplets double their mass due to radiation in their time at cloud top. This simulated droplet size distribution matches the flight measurements, confirming that condensation due to long-wave radiation can be an important mechanism for broadening the droplet-size-distribution in radiatively-driven stratocumulus.
Bromine atom production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska
Authors: Thompson Chelsea R. , Shepson Paul B. , Liao Jin , Huey L. Greg , Cantrell Chris , Flocke Frank , Orlando John
Published: January 2016

Abstract. Ozone depletion events (ODEs) in the Arctic are primarily controlled by a bromine radical-catalyzed destruction mechanism that depends on the efficient production and recycling of Br atoms. Numerous laboratory and modeling studies have suggested the importance of heterogeneous recycling of Br through HOBr reaction with bromide on saline surfaces. However, the gas-phase regeneration of bromine atoms through BrO-BrO radical reactions has been assumed to be an efficient, if not dominant, pathway for Br reformation and thus ozone destruction. Indeed, it has been estimated that the rate of ozone depletion is approximately equal to twice the rate of the BrO self-reaction. Here, we use a zero-dimensional, photochemical model, largely constrained to observations of stable atmospheric species from the 2009 OASIS campaign in Barrow, Alaska, to investigate gas-phase bromine radical propagation and heterogeneous recycling of bromine for a seven-day period during late March. We find that the gas-phase bromine chain length is quite small, at <1.5, and is highly dependent on ambient O3 concentrations. As a result, ozone depletion rates estimated from only gas-phase BrO-radical reactions may significantly underestimate the rate of ozone loss. Furthermore, we find that Br atom production from primary surface emission of Br2 and BrCl can account for between 30 – 90% of total Br atom production. This analysis suggests that heterogeneous recycling of bromine is at least as important as, and at times greater than, gas-phase recycling for the occurrence of Arctic ODEs.
Impacts of the Manaus pollution plume on the microphysical properties of Amazonian warm-phase clouds in the wet season
Authors: Cecchini Micael A. , Machado Luiz A. T , Comstock Jennifer M. , Mei Fan , Wang Jian , Fan Jiwen , Tomlinson Jason M. , Schmid Beat , Albrecht Rachel , Martin Scot T. , Artaxo Paulo
Published: January 2016

Abstract. The remote atmosphere over the Amazon can be similar to oceanic regions in terms aerosol conditions and cloud type formations. This is especially true during the wet season. The main aerosol-related disturbances over the Amazon have both natural sources, such as dust transport from Africa, and anthropogenic sources, such as biomass burning or urban pollution. The present work considers the impacts of the latter on the microphysical properties of warm-phase clouds by analyzing observations of the interactions between Manaus city and its surroundings, as part of the GoAmazon2014/5 Experiment. The analyzed period corresponds to the wet season over a tropical rain forest (i.e., Feb to Mar 2014 and corresponding to the first Intensive Operating Period (IOP1) of GoAmazon2014/5), and the droplets observed are in the range 1 μm ≤ D ≤ 50 μm. The wet season largely presents a clean background atmosphere characterized by frequent rain showers. As such, the contrast between background clouds compared to those affected by the Manaus pollution can be observed and detailed. The focus is on the characteristics of the initial microphysical properties in cumulus clouds predominantly at their early stages. The pollution-affected clouds are found to have lower effective diameters and higher droplet number concentrations. The average differences range from 10% to 40% for the effective diameter and are as high as 1000% for droplet concentration across different vertical levels (0 to 3200 m). The growth rates of droplets with altitude are slower for pollution-affected clouds (2.90 compared to 5.59 μm km-1), as explained by the absence of bigger droplets at the onset of cloud development. Clouds under background conditions have higher concentrations of larger d roplets (e.g., > 20 μm) close to cloud base, which would contribute significantly to the growth rates through the collision-coalescence process. The droplet size distribution (DSD) overall shape do not appear to be predominantly determined by updraft strength, especially beyond the 20 μm range. The aerosol conditions play a major role in that case. However, the updrafts modulate the DSD concentrations and are responsible for the vertical transport of water in the cloud. The larger droplets found in background clouds are associated with weak water vapour competition and a bimodal distribution of droplets in the lower levels of the cloud, that enables an earlier initiation of collision-coalescence process. This study shows that the pollution produced by Manaus affects significantly warm-phase microphysical properties of the surrounding clouds by changing the initial DSD formation. The corresponding effects on ice-phase processes and precipitation formation should be the focus of future endeavors.
Typical synoptic situations and their impacts on the wintertime air pollution in the Guanzhong basin, China
Authors: Bei N. , Li G. , Huang R. , Cao J. , Meng N. , Feng T. , Liu S. , Zhang T. , Zhang Q. , Molina L. T.
Published: January 2016

Abstract. Rapid industrialization and urbanization have caused severe air pollution in the Guanzhong basin, northwestern China with heavy haze events occurring frequently in recent winters. Using the NCEP reanalysis data, the large scale synoptic situations influencing the Guanzhong basin during wintertime of 2013 are categorized into six types to evaluate the contribution of synoptic situations to the air pollution, including "north-low", "southwest-trough", "southeast-high", "transition", "southeast-trough", and "inland-high". The FLEXPART model has been utilized to demonstrate the corresponding pollutant transport patterns for the typical synoptic situations in the basin. Except "southwest-trough" and "southeast-high" (defined as favorable synoptic situations), the rest four synoptic conditions (defined as unfavorable synoptic situations) generally facilitate the accumulation of air pollutants, causing heavy air pollution in the basin. In association with the measurement of PM2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) in the basin, the unfavorable synoptic situations correspond to high PM2.5 mass concentrations or poor air quality and vice versa. The same analysis has also been applied to winters of 2008–2012, which shows that the basin was mainly influenced by the unfavorable synoptic situations during wintertime leading to poor air quality. The WRF-CHEM model has further been applied to simulate the selected six days representing the typical synoptic situations during the wintertime of 2013, and the results generally show a good consistence between the modeled distributions and variations of PM2.5 and the corresponding synoptic situations, demonstrating reasonable classification for the synoptic situations in the basin. Detailed meteorological conditions, such as temperature inversion, low-level horizontal wind speed, vertical wind velocity, and convergence all contribute to heavy air pollution events in the basin under unfavorable synoptic conditions. Considering the proportion of occurrence of unfavorable synoptic situations during wintertime, reduction of emissions is the optimum approach to mitigate the air pollution in the Guanzhong basin.
Photochemical age of air pollutants and oxidation products in transboundary air observed on Fukue Island, Nagasaki, Japan
Authors: Irei S. , Takami A. , Sadanaga Y. , Nozoe S. , Yonemura S. , Bandow H. , Yokouchi Y.
Published: January 2016

Abstract. To better understand the secondary air pollution in transboundary air over westernmost Japan, ground-based field measurements of the chemical composition of fine particulate matter (≤ 1 μm), mixing ratios of trace gases species (CO, O3, NOx, NOy, i-pentane, toluene, and ethyne), and meteorological elements were conducted with a suite of instrumentation. The CO mixing ratio dependence on wind direction showed that there was no notable influence from primary emission sources near the monitoring site, indicating long- and/or mid-range transport of the measured chemical species. Despite the considerably different atmospheric lifetimes of NOy and CO, these mixing ratios were correlated (r2 = 0.67), suggesting negligible loss of NOy by the reaction with OH radical. The photochemical age of the pollutants, t[OH], was calculated from both the NOx / NOy concentration ratio (NOx / NOy clock) and the toluene/ethyne concentration ratio (hydrocarbon clock). It was found that the toluene/ethyne concentration ratio was significantly influenced by dilution with background air containing 0.16 ppbv of ethyne, causing significant bias in the estimation of t[OH]. In contrast, the influence of the reaction of NOx with O3, a potentially biasing reaction channel on [NOx] / [NOy], was small. The t[OH] values obtained with the NOx / NOy clock were compared with the fractional contribution of the m/z 44 signal to the total signal in the organic aerosol mass spectra (f44, a quantitative oxidation indicator of carboxylic acids), and the comparison showed evidence for a systematic increase of f44 as t[OH] increased. To a first approximation, the f44 increase rate was 1.05 × 10−9 h−1 molecule−1 cm3, which is comparable to the background-corrected increase rate observed during the New England Air Quality Study in summer 2002.
Polarization properties of aerosol particles over western Japan: classification, seasonal variation, and implications for air quality
Authors: Pan X. L. , Uno I. , Hara Y. , Osada K. , Yamamoto S. , Wang Z. , Sugimoto N. , Kobayashi H. , Wang Z. F.
Published: January 2016

Abstract. Ground-based observations of the polarization properties of aerosol particles using a polarization optical particle counter (POPC) were performed from October 2013 to January 2015 at a suburban site in the Kyushu area of Japan. By conducting an analysis of online measurements of aerosol composition, we investigated size-dependent polarization characteristics for three typical aerosol types (anthrop ogenic pollutants, dust, and sea salt). We found that, for supermicron particles, its depolarization ratio (DR, the fraction of s-polarized signal in the total back ward light scattering signal) generally increased with the particle size, and a threshold value of 0.1 could be used to identify the irsphericity. In summer, air pollution was less serious, and the DR of aerosol particles was relatively small due to the influence of spherical sea salt particles in high humidity conditions. This study indicated that air masses were transported across the Asian continent and contained not only anthropogenic pollutants, but also large amounts of non-spherical particles (i.e., dust), which could impact on the air quality in western Japan, especially in winter and spring. The variation of number fraction of spherical particles did not correlate with relative humidity averaged along the trajectories of air parcels, indicating the coexistence of hydrophobic substances (e.g., mineral dust and organics), although the sulfate and nitrate mass concentrations were high.
A DNS study of aerosol and small-scale cloud turbulence interaction
Authors: Babkovskaia N. , Rannik U. , Phillips V. , Siebert H. , Wehner B. , Boy M.
Published: January 2016

Abstract. The purpose of this study is to investigate the effect of aerosol dynamics (evaporation/condensation) on atmospheric small-scale turbulence (and vice versa) using direct numerical simulations (DNS). We consider the domain located on the height of about 2000 m from the sea level, experiencing transient high supersaturation due to atmospheric fluctuations of temperature and humidity. To study the effect of aerosol dynamics on the turbulence we vary the total number of particles (Ntot). In turn, to investigate the effect of small-scale turbulence on evolution of aerosol particles we vary the intensity of turbulent fluctuations and the buoyant force. We find that even small amount of aerosol particles (55.5 cm−3) increases the air temperature by 1 K under supersaturated conditions due to release of latent heat. The system comes to an equilibrium faster and the relative number of activated particles appears to be smaller for larger Ntot. We conclude that the presence of aerosol particles results in deceleration of air motion in vertical direction and damping of turbulent fluctuations.
Local short-term variability in solar irradiance
Authors: Lohmann Gerald M. , Monahan Adam H. , Heinemann Detlev
Published: January 2016

Abstract. Characterizing spatio-temporal irradiance variability is important for the successful grid integration of increasing numbers of photovoltaic (PV) power systems. Using 1 Hz data recorded by as many as 99 pyranometers during the HD(CP)2 Observational Prototype Experiment HOPE, we analyze field variability of clearsky index k∗ (i.e. irradiance normalized to clearsky conditions) and sub-minute k∗ increments (i.e. changes over specified intervals of time) for distances between tens of meters and about ten kilometers. By means of a simple classification scheme based on k∗ statistics, we identify overcast, clear and mixed sky conditions, and demonstrate that the last of these is the most potentially problematic in terms of short-term PV power fluctuations. Under mixed conditions, the probability of relatively strong k∗ increments of ±0.5 is approximately twice as high compared to increment statistics computed without conditioning by sky type. As well, spatial autocorrelation structures of k∗ increment fields differ considerably between sky types. While the profiles for overcast and clear skies mostly resemble the predictions of a simple model published by Hoff and Perez (2012), this is not the case for mixed conditions. As a proxy for the smoothing effects of distributed PV, we finally show that spatial averaging mitigates variability in k∗ less effectively than variability in k∗ increments, for a spatial sensor density of 2 km−2.