Description: Atmosphere, Vol. 9, Pages 370: A Comprehensive Approach to Assess the Hydrological Drought of Inland River Basin in Northwest China Atmosphere doi: 10.3390/atmos9100370 Authors: Nina Zhu Jianhua Xu Weihong Li Kaiming Li Cheng Zhou How to measure and quantitatively assess hydrological drought (HD) in the inland river basins of Northwest China is a difficult problem because of the complicated geographical environment and climatic processes. To address this problem, we conducted a comprehensive approach and selected the Aksu River Basin (ARB) as a typical inland river basin to quantitatively assess the hydrological drought based on the observed data and reanalysis data during the period of 1980–2010. We used two mutual complementing indicators, i.e., the standardized runoff index (SRI) and standardized terrestrial water storage index (SWSI), to quantitatively measure the spatio-temporal pattern of HD, where the SRI calculated from the observed runoff data indicate the time trend of HD of the whole basin, while SWSI extracted from the reanalysis data indicate the spatial pattern of HD. We also used the auto-regressive distribution lag model (ARDL) to show the autocorrelation of HD and its dependence on precipitation, potential evapotranspiration (PET), and soil moisture. The main conclusions are as follows: (a) the western and eastern regions of the ARB were prone to drought, whereas the frequency of drought in the middle of the ARB is relatively lower; (b) HD presents significant autocorrelation with two months’ lag, and soil moisture is correlated with SWSI with two months’ lag, whereas PET and precipitation are correlated with SWSI with 1 month’ lag; (c) the thresholds of HD for annual PET, annual precipitation, and annual average soil moisture are greater than 844.05 mm, less than 134.52 mm, and less than 411.07 kg/m2, respectively. A drought early warning system that is based on the thresholds was designed.

Description: Atmosphere, Vol. 9, Pages 368: Particle-Bound Polycyclic Aromatic Hydrocarbon in the Atmosphere of Heavy Traffic Areas in Greater Cairo, Egypt: Status, Source, and Human Health Risk Assessment Atmosphere doi: 10.3390/atmos9100368 Authors: Salwa Kamal Hassan Airborne particulate samples were collected from three main squares (Ramsis, El Giza, and Sphinx) representing heavy traffic areas in Greater Cairo during the period of December 2015–February 2016, and analysed for polycyclic aromatic hydrocarbon (PAHs). The maximum concentrations of particle-bound PAHs were observed at El Giza, while the minimum levels were recorded at Sphinx. The levels of particle-bound PAHs in the square areas of Greater Cairo are higher than those found in many different locations in Egypt and around the world.The distribution of individual particle-bound PAHs as well as PAH categories, depending on the ring number in Ramsis, El Giza, and Sphinx, wasquite similar. This similarity implies similar emission sources of PAHs in the three square areas, with vehicle exhaust emissions being the dominant one. Benzo[b]fluoranthene (BbF), benzo[ghi]perylene (BGP), and indeno[1,2,3-cd]pyrene(IND) were the most abundant PAH compounds. Diagnostic concentration ratios of PAH compounds in the three square locations suggest that both petrogenic and pyrogenic sources emit these compounds. Moreover, they originate mainly from traffic emissions in the study areas. Based on the calculated benzo[a]pyrene equivalent (BaPeq) for the individual particle-bound PAH compounds, health risks associated with the inhalation of these compounds were assessed. Total carcinogenic activity (TCA) for all measured PAHs represented 20.03% (El Giza), 20.40% (Ramsis), and 20.60% (Sphinx) of the total PAH concentrations. Benzo[a]pyrene (BaP) and dibenz[a,h]anthracene (DBA) were the highest contributors to the total health risks; these accounted for 42.72% and 38.50% (El Giza), 41.79% and 39.17% (Ramsis), and 42.92% and 37.78% (Sphinx) of the TCA of all PAH compounds, respectively. These results indicate the importance of BaP and DBA as surrogate compounds for PAHs in the atmosphere of square areas of Greater Cairo.

Description: Atmosphere, Vol. 9, Pages 369: Characterization of In Situ Aerosol Optical Properties at Three Observatories in the Central Mediterranean Atmosphere doi: 10.3390/atmos9100369 Authors: Antonio Donateo Teresa Lo Feudo Angela Marinoni Adelaide Dinoi Elenio Avolio Eva Merico Claudia Roberta Calidonna Daniele Contini Paolo Bonasoni In this work, results of scattering and backscattering coefficients, scattering Ångström exponent (SAE), single scattering albedo (SSA), and asymmetry parameter (g) of atmospheric aerosols are presented. All these parameters were measured during the month of April 2016 in Southern Italy on three different Global Atmosphere Watch observatories in the Central Mediterranean. This is the first time, to our knowledge, that optical aerosol properties were studied at the same time, even if in a brief intensive measurement campaign, at three sites in the South of Italy. In order to obtain a characteristic value for aerosol optical properties, different kinds of particle sources (i.e., dust, marine, and anthropic) have been identified and studied. In the measurement period, one event of a long-range transport of Saharan dust from Northern Africa was observed at all observatories. During the Saharan dust transport event, a minimum value of the SAE (0.69 ± 0.34) and a relatively higher values of SSA were observed. During the dust event, g increased up to 0.69. Marine aerosol contribution and anthropic/urban aerosol intrusion were analysed. From this analysis, SAE average values were 0.70, 0.84, and 1.22, respectively, for dust, marine, and anthropic particles. On the other hand, the SSA minimum value was 0.86 for anthropic particles, and it increased for dust (0.88) and marine (0.93) aerosols. The asymmetry parameter had a limited variability for the three types of aerosol from 0.62 to 0.58, as reported also in literature.

Description: Atmosphere, Vol. 9, Pages 367: Diurnal and Seasonal Variations of Carbon Dioxide (CO2) Concentration in Urban, Suburban, and Rural Areas around Tokyo Atmosphere doi: 10.3390/atmos9100367 Authors: Ryoichi Imasu Yuka Tanabe Site environments and instrumental characteristics of carbon dioxide (CO2) measurements operated by local governments in the Kanto Plain, the center of which is Tokyo, were summarized for this study. The observation sites were classified into environments of three types: urban, suburban, and woodland. Based on a few decades of accumulated hourly data, the diurnal and seasonal variations of CO2 concentrations were analyzed as a composite of anomalies from annual means recorded for each site. In urban areas, the highest concentrations appear before midnight in winter. The second peak corresponds to the morning rush hour and the strengthening of the inversion layer. Suburban areas can be characterized as having the highest concentration before dawn and the lowest concentration during the daytime in summer in association with the activation of respiration and photosynthesis of vegetation. In these areas, concentration peaks also appear during the morning rush hour. Woodland areas show background features, with the highest concentration in early spring, which are higher than the global background by about 5 ppmv.

Description: Atmosphere, Vol. 9, Pages 366: Impacts of Different Onset Time El Niño Events on Winter Precipitation over South China Atmosphere doi: 10.3390/atmos9100366 Authors: Lingli Fan Jianjun Xu Huade Guan Winter precipitation over South China tended to be much higher than normal for the spring El Niño events during 1979–2016. For the spring El Niño events, the meridional and zonal circulations served as a bridge, linking the warmer sea surface temperature (SST) in the eastern equatorial Pacific (EEP) and South China winter precipitation. This possible physical process can be described as follows: During boreal winter, a positive SST anomaly in the EEP was concurrent with strong anomalous convection activity over South China via anomalous Walker circulation, an anomalous Hadley Cell along 110°–130° E, and a zonal westward teleconnection wave train pattern at 700 hPa in the Northern Hemisphere. In addition, an anomalous pumping effect at 200 hPa contributed to the convective activity. Meanwhile, the western Pacific subtropical high moved southwards and strengthened at 500 hPa, and abnormal southwesterly winds brought plentiful water vapor to South China at 850 hPa. All these factors favored an increase in precipitation over South China. For the summer El Niño events, the aforementioned anomalies were weaker, which resulted in a precipitation close to normal over South China.

Description: Atmosphere, Vol. 9, Pages 365: Contributions of Atmospheric Transport and Rain–Vapor Exchange to Near-Surface Water Vapor in the Zhanjiang Mangrove Reserve, Southern China: An Isotopic Perspective Atmosphere doi: 10.3390/atmos9090365 Authors: Xiang Lai Jonathon S. Wright Wenyu Huang Jie Liang Guanghui Lin Shanxian Zhu Coastal mangroves are increasingly recognized as valuable natural resources and important sites of water and carbon exchange. In this study, we examine atmospheric water cycling in the boundary layer above a coastal mangrove forest in southern China. We collected site observations of isotopic ratios in water vapor and precipitation along with core meteorological variables during July 2017. Our evaluation of these data highlights the influences of large-scale atmospheric transport and rain–vapor exchange in the boundary layer water budget. Rain–vapor exchange takes different forms for different types of rainfall events. The evolution of isotopic ratios in water vapor suggests that substantial rain recycling occurs during the passage of large-scale organized convective systems, but that this process is much weaker during rainfall associated with less organized events of local origin. We further examine the influences of large-scale transport during the observation period using a Lagrangian trajectory-based moisture source analysis. More than half (63%) of the boundary layer moisture during the study period traced back to the South China Sea, consistent with prevailing southerly to southwesterly flow. Other important moisture sources included mainland Southeast Asia and the Indian Ocean, local land areas (e.g., Hainan Island and the Leizhou Peninsula), and the Pacific Ocean. Together, these five regions contributed more than 90% of the water vapor. The most pronounced changes in isotopic content due to large-scale transport during the study period were related to the passage of Tropical Storm Talas. The outer rain bands of this tropical cyclone passed over the measurement site on 15–17 July, causing a sharp reduction in the heavy isotopic content of boundary layer water vapor and a substantial increase in deuterium excess. These changes are consistent with extensive isotopic distillation and rain–vapor exchange in downdrafts associated with the intense convective systems produced by this storm.

Description: Atmosphere, Vol. 9, Pages 364: Single Scattering Albedo’s Spectral Dependence Effect on UV Irradiance Atmosphere doi: 10.3390/atmos9090364 Authors: Ioannis-Panagiotis Raptis Stelios Kazadzis Kostas Eleftheratos Vassilis Amiridis Ilias Fountoulakis The absorbing and scattering nature of aerosols affects the total radiative forcing and is quantified by single scattering albedo (SSA), which is defined as the absorption to total extinction ratio. There are limited measurements of SSA in the ultraviolet (UV) irradiance spectrum, hence, the influence of SSA on incoming UV irradiance has not been explored in great depth. In the present study, UV irradiance was calculated and compared using different SSA datasets retrieved at Athens, Greece during 2009–2014; including SSA time series from Ultraviolet Multi-Filter Radiometer (UVMFR) at 332 and 368 nm, SSA from AERONET at 440 nm, from OMI satellite at 342.5 nm and AeroCom climatological database at 300 nm. Irradiances were estimated using a radiative transfer model (RTM). Comparisons of these results revealed that relative differences of UVA and UVB could be as high as 20%, whilst average relative differences varied from 2% to 8.7% for the entire experimental period. Both UVA and UVB drop by a rate of ~12% for 0.05 aerosol absorption optical depth in comparison to ones estimated with the use of SSA at visible range. Brewer irradiance measurements at 324 nm were used to validate modeled monochromatic irradiances and a better agreement was found when UVMFR SSAs were used with an average difference of 0.86%. However, when using visible or climatological input, relative differences were estimated +4.91% and +4.15% accordingly.

Description: Atmosphere, Vol. 9, Pages 363: Impact of Air Mass Conditions and Aerosol Properties on Ice Nucleating Particle Concentrations at the High Altitude Research Station Jungfraujoch Atmosphere doi: 10.3390/atmos9090363 Authors: Larissa Lacher Martin Steinbacher Nicolas Bukowiecki Erik Herrmann Assaf Zipori Zamin A. Kanji Ice nucleation is the source of primary ice crystals in mixed-phase clouds. Only a small fraction of aerosols called ice nucleating particles (INPs) catalyze ice formation, with their nature and origin remaining unclear. In this study, we investigate potential predictor parameters of meteorological conditions and aerosol properties for INP concentrations at mixed-phase cloud condition at 242 K. Measurements were conducted at the High Altitude Research Station Jungfraujoch (Switzerland, 3580 m a.s.l.), which is located predominantly in the free troposphere (FT) but can occasionally receive injections from the boundary layer (BLI). Measurements are taken during a long-term study of eight field campaigns, allowing for the first time an interannual (2014–2017) and seasonal (spring, summer, and winter) distinction of high-time-resolution INP measurements. We investigate ranked correlation coefficients between INP concentrations and meteorological parameters and aerosol properties. While a commonly used parameterization lacks in predicting the observed INP concentrations, the best INP predictor is the total available surface area of the aerosol particles, with no obvious seasonal trend in the relationship. Nevertheless, the predicting capability is less pronounced in the FT, which might be caused by ageing effects. Furthermore, there is some evidence of anthropogenic influence on INP concentrations during BLI. Our study contributes to an improved understanding of ice nucleation in the free troposphere, however, it also underlines that a knowledge gap of ice nucleation in such an environment exists.

Description: Atmosphere, Vol. 9, Pages 360: Influence of Disdrometer Type on Weather Radar Algorithms from Measured DSD: Application to Italian Climatology Atmosphere doi: 10.3390/atmos9090360 Authors: Elisa Adirosi Nicoletta Roberto Mario Montopoli Eugenio Gorgucci Luca Baldini Relations for retrieving precipitation and attenuation information from radar measurements play a key role in radar meteorology. The uncertainty in such relations highly affects the precipitation and attenuation estimates. Weather radar algorithms are often derived by applying regression methods to precipitation measurements and radar observables simulated from datasets of drop size distributions (DSD) using microphysical and electromagnetic assumptions. DSD datasets can be derived from theoretical considerations or obtained from experimental measurements collected throughout the years by disdrometers. Although the relations obtained from experimental disdrometer datasets can be generally considered more representative of a specific climatology, the measuring errors, which depend on the specific type of disdrometer used, introduce an element of uncertainty to the final retrieval algorithms. Eventually, data quality checks and filtering procedures applied to disdrometer measurements play an important role. In this study, we pursue two main goals: (i) evaluate two different techniques for establishing weather radar algorithms from measured DSD, and (ii) investigate to what extent dual-polarization radar algorithms derived from experimental DSD datasets are influenced by the different error structures introduced by the various disdrometer types (namely 2D video disdrometer, first and second generation of OTT Parsivel disdrometer, and Thies Clima disdrometer) used to collect the data. Furthermore, weather radar algorithms optimized for Italian climatology are presented and discussed.

Description: Atmosphere, Vol. 9, Pages 359: Characteristics of Atmospheric Boundary Layer Structure during PM2.5 and Ozone Pollution Events in Wuhan, China Atmosphere doi: 10.3390/atmos9090359 Authors: Yassin Mbululo Jun Qin Jun Hong Zhengxuan Yuan In this study, we investigated six air pollutants from 21 monitoring stations scattered throughout Wuhan city by analyzing meteorological variables in the atmospheric boundary layer (ABL) and air mass backward trajectories from HYSPLIT during the pollution events. Together with this, ground meteorological variables were also used throughout the investigation period: 1 December 2015 to 30 November 2016. Analysis results during this period show that the city was polluted in winter by PM2.5 (particulate matter with aerodynamics of less than 2.5 microns) and in summer by ozone (O3). The most polluted day during the investigation period was 25 December 2015 with an air quality index (AQI) of 330 which indicates ‘severe pollution’, while the cleanest day was 26 August 2016 with an AQI of 27 indicating ‘excellent’ air quality. The average concentration of PM2.5 (O3) on the most polluted day was 265.04 (135.82) µg/m3 and 9.10 (86.40) µg/m3 on the cleanest day. Moreover, the percentage of days which exceeded the daily average limit of NO2, PM10, PM2.5, and O3 for the whole year was 2.46%, 14.48%, 23.50%, and 39.07%, respectively, while SO2 and CO were found to be below the set daily limit. The analysis of ABL during PM2.5 pollution events showed the existence of a strong inversion layer, low relative humidity, and calm wind. These observed conditions are not favorable for horizontal and vertical dispersion of air pollutants and therefore result in pollutant accumulation. Likewise, ozone pollution events were accompanied by extended sunshine hours, high temperature, a calm wind, a strongly suspended inversion layer, and zero recorded rainfall. These general characteristics are favorable for photochemical production of ozone and accumulation of pollutants. Apart from the conditions of ABL, the results from backward trajectories suggest trans-boundary movement of air masses to be one of the important factors which determines the air quality of Wuhan.