Atmosphere, Volume 8, Issue 5 (May 2017) – 15 articles

To investigate the mechanism of available energy partitioning to sensible and latent heat fluxes over semi-arid regions, data from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) were analyzed to assess the effects of soil moisture, net radiation, and vapor pressure deficit (VPD) on available energy partitioning, as quantified by Bowen ratio. It was found that the Bowen ratio decreased rapidly with increasing soil moisture when soil was dry but was insensitive to the change in soil moisture when soil became wet. Net radiation and VPD affected the sensitivity of the Bowen ratio to soil moisture under dry conditions and the soil moisture threshold above which the Bowen ratio became insensitive to soil moisture. The Bowen ratio increases with net radiation at a high level of VPD, while the Bowen ratio first increases and then decreases with net radiation at a low level of VPD. Reduced soil moisture enhanced the effects of the net radiation and VPD on available energy partitioning. The effects of the VPD on Bowen ratio depended on the relative strength of the positive and negative impacts of VPD on the latent heat flux under different soil and net radiation conditions. Full article

We conducted global warming projections using the Meteorological Research Institute-Atmospheric General Circulation Model Version 3.2 with a 60-km grid size (MRI-AGCM3.2H). For the present-day climate of 21 years from 1983 through 2003, the model was forced with observed historical sea surface temperature (SST). For the future climate of 21 years from 2079–2099, the model was forced with future SST projected by conventional couple models. Twelve-member ensemble simulations for three different cumulus convection schemes and four different SST distributions were conducted to evaluate the uncertainty of projection. Annual average precipitation will increase over the equatorial regions and decrease over the subtropical regions. The future precipitation changes are generally sensitive to the cumulus convection scheme, but changes are influenced by the SST over the some regions of the Pacific Ocean. The precipitation efficiency defined as precipitation change per 1° surface air temperature warming is evaluated. The global average of precipitation efficiency for annual average precipitation was less than the maximum value expected by thermodynamical theory, indicating that dynamical atmospheric circulation is acting to reduce the conversion efficiency from water vapor to precipitation. The precipitation efficiency by heavy precipitation is larger than that by moderate and weak precipitation. Full article

In this study, 24 h PM_2.5 (particles with an equivalent diameter equal to or below 2.5 μm) samples were collected in winter and summer in Xi’an, Northwestern China to characterize the seasonal variations of eleven elements (As, Cd, Cr, Fe, K, Mn, Mo, Pb, Ni, Zn, and Cu) and to evaluate their health risks by using the US EPA (U.S. Environmental Protection Agency) method. Mass concentrations of the elements (except Ni) in winter were much higher than those in summer, with similar variations for both seasons. The levels of elements followed a decreasing order of K > Zn > Fe > Pb > Cr > As > Mn > Cu > Mo > Ni > Cd. According to the enrichment factor (EF) analysis, the highest EF value for Cd inferred that it should be linked with the metal smelting and other anthropogenic sources. In contrast, the EF values of K and Mn (1 < EF < 5) suggested that they were influenced by both natural and anthropogenic sources. The daily average exposure dose for children and adults by different exposure pathways were both ingestion > dermal contact > inhalation. The non-cancer risks for different exposure pathways showed different orders. The non-cancer risks (hazard quotients) were lower than the average risk threshold (1.0) except for As, Pb, and Cr, which require greater attention. Elements of As and Cr were higher than the cancer risk threshold value (1 × 10⁻⁶), indicating that the cancer risks of PM_2.5 elements in Xi’an should be a concern. Full article

In November 2011, an Atlantic depression affected the Mediterranean basin, eventually evolving into a Tropical-Like Cyclone (TLC or Mediterranean Hurricane, usually designated as Medicane). In the region affected by the Medicane, mean sea level pressures down to 990 hPa, wind speeds of hurricane intensity close to the eye (around 115 km/h) and intense rainfall in the prefrontal zone were reported. The intensity of this event, together with its long permanence over the sea, suggested its suitability as a paradigmatic case for investigating the sensitivity of a numerical modeling system to different configurations, air-sea interface parameterizations and coupling approaches. Toward this aim, a set of numerical experiments with different parameterization schemes and levels of coupling complexity was carried out within the Coupled Ocean Atmosphere Wave Sediment Transport System (COAWST), which allows the description of air-sea dynamics by coupling an atmospheric model (WRF), an ocean circulation model (ROMS), and a wave model (SWAN). The sensitivity to different initialization times and Planetary Boundary Layer (PBL) parameterizations was firstly investigated by running a set of WRF standalone (atmospheric-only) simulations. In order to better understand the effect of coupling on the TLC formation, intensification and trajectory, different configurations of atmosphere-ocean coupling were subsequently tested, eventually including the full coupling among atmosphere, ocean and waves, also changing the PBL parameterization and the formulation of the surface roughness. Results show a strong sensitivity of both the trajectory and the intensity of this TLC to the initial conditions, while the tracks and intensities provided by the coupled modeling approaches explored in this study do not introduce drastic modifications with respect to those resulting from a fine-tuned standalone atmospheric run, though they provide by definition a better physical and energetic consistency. Nevertheless; the use of different schemes for the calculation of the surface roughness from wave motion, which reflects the description of air-sea interface processes, can significantly affect the results in the fully coupled runs. Full article

The ‘Hestia Project’ uses a bottom-up approach to quantify fossil fuel CO₂ (FFCO₂) emissions spatially at the building/street level and temporally at the hourly level. Hestia FFCO₂ emissions are provided in the form of a group of sector-specific vector layers with point, line, and polygon sources to support carbon cycle science and climate policy. Application to carbon cycle science, in particular, requires regular gridded data in order to link surface carbon fluxes to atmospheric transport models. However, the heterogeneity and complexity of FFCO₂ sources within regular grids is sensitive to spatial resolution. From the perspective of a data provider, we need to find a balance between resolution and data volume so that the gridded data product retains the maximum amount of information content while maintaining an efficient data volume. The Shannon entropy determines the minimum bits that are needed to encode an information source and can serve as a metric for the effective information content. In this paper, we present an analysis of the Shannon entropy of gridded FFCO₂ emissions with varying resolutions in four Hestia study areas, and find: (1) the Shannon entropy increases with smaller grid resolution until it reaches a maximum value (the max-entropy resolution); (2) total emissions (the sum of several sector-specific emission fields) show a finer max-entropy resolution than each of the sector-specific fields; (3) the residential emissions show a finer max-entropy resolution than the commercial emissions; (4) the max-entropy resolution of the onroad emissions grid is closely correlated to the density of the road network. These findings suggest that the Shannon entropy can detect the information effectiveness of the spatial resolution of gridded FFCO₂ emissions. Hence, the resolution-entropy relationship can be used to assist in determining an appropriate spatial resolution for urban CO₂ flux studies. We conclude that the optimal spatial resolution for providing Hestia total FFCO₂ emissions products is centered around 100 m, at which the FFCO₂ emissions data can not only fully meet the requirement of urban flux integration, but also be effectively used in understanding the relationships between FFCO₂ emissions and various social-economic variables at the U.S. census block group level. Full article

The decomposition kinetics of non-volatile n-alkanes that were collected in an urban environment were studied. The quartz filters that they were collected on were exposed in two reactors, in dark and natural light conditions, for four days. Ambient air that was passed through the reactors continuously, ensured a supply of exogenic oxidants to the surface of the filters. The lifetimes of the non-volatile n-alkanes were experimentally determined to be in the order of 3–6 days. The results from the light reactor exhibited approximately a 10% decrease in their lifetime. The results obtained for the prevailing atmospheric conditions and for the duration of the experiments, were in agreement with values from the literature. Full article

Burning agricultural straw before and/or after harvest is a common farming practice. Regional and extensive agricultural open field straw burning can cause serious air pollution events. This paper looks at the effects of biomass burning emission on regional haze that should be considered in the forecasting of regional haze. It describes the current state of crop residue burning in China, and analyzes the relationship between biomass burning and regional haze in terms of temporal/spatial patterns and chemical composition. Finally, some suggestions/recommendations are proposed for the recycling of agricultural straw to reduce the impact of biomass burning on regional haze and air quality. We suggest that prescribed open burning would be a more suitable solution in China. We hope that this report about biomass burning and regional haze will bring the issue to the attention of governments and other researchers. Full article

This study considers the role of distance to the African source on the amount of deposition. To this end, dry and wet deposition was measured at a site close to Africa (Santa Cruz de Tenerife in the Canary Islands, SCO) and at a distant site located in NE Spain (La Castanya, Montseny, MSY). Because of the important influence of African influence on the buildup of particles in the atmosphere, we specifically addressed the contribution of North African events (NAF events) compared to other provenances (no-NAF events) in the wet and dry pathways at the two sites. At the site close to Africa, most of the crustal-derived elements were deposited in the dry mode, with NAF events contributing more than no-NAF events. Marine elements, by contrast, were mostly deposited at this site in the wet form with a predominance of no-NAF events. At MSY, wet deposition of SO₄–S, NO₃–N and NH₄–N during NAF events was higher than at the site close to Africa, either in the wet or dry mode. This fact suggests that mineral dust interacts with pollutants, the mineral surface being coated with ammonium, sulphate and nitrate ions as the dust plume encounters polluted air masses in its way from North Africa to the Western Mediterranean. African dust may provide a mechanism of pollution scavenging and our results indicate that this removal is more effective in the wet mode at sites far away from the mineral source. Full article

Methane (CH₄) from enteric fermentation is one of the main anthropogenic greenhouse gas (GHG) emissions in South Africa. Livestock population data from 1990 to 2014 and emission factors were utilized in estimating CH₄ emissions as per the 2006 IPCC (Intergovernmental Panel on Climate Change) guidelines. CH₄ emissions originating from country-specific emission factors were compared with those calculated using IPCC default emission factors. Trends in emissions were then determined using the Man-Kendall trend test at the 5% significance level. The results showed annual total enteric CH₄ emissions exceeding 1171.56 Gg (in 1995) with an average (1990 to 2014) of 1227.96 Gg. Non-dairy cattle are the highest emitters with an average of 873.07 Gg (71.10%) while sheep are the second highest with 227.61 Gg (18.54%). Other contributors are dairy cattle, goats, horses, pigs and donkeys with an average (percentage contribution) of 85.94 Gg (7.00%), 32.06 Gg (2.61%), 4.86 Gg (0.40%), 2.77 Gg (0.23%) and 1.65 Gg (0.13%), respectively. The trend analysis revealed positive trends for all the livestock categories, except sheep and goats which showed negative trends, consequently balancing out. The results obtained for the year 2014 were 37% higher than the enteric CH₄ emissions in 1990, 1994 and 2000 inventories and the emissions estimated entirely from IPCC default emission factors. This demonstrates the need for the development of Tier 2 emission factors for key category sectors such as cattle and sheep in South Africa. To fully adhere to the principles of GHG inventory accounting, there has to be total livestock inclusivity and major improvements in activity data collection. Full article

As the main anthropogenic greenhouse gas that contributes most to global warming, CO₂ plays an important role in climate changes in Central Asia. Due to the lack of studies of near-surface CO₂ in this region, we first confirmed the applicability of the near-surface Greenhouse Gases Observing Satellite (GOSAT) CO₂ data in Central Asia using atmospheric CO₂ concentration data from nine ground-based station observations. We then analyzed the temporal and spatial distributions of the near-surface CO₂ concentrations in Central Asia and their controlling factors using statistical analysis methods. The results show that the near-surface CO₂ concentrations are high in the western part of this region and low in the east. From June 2009 to May 2013, the near-surface CO₂ concentrations increased gradually, with the highest value being in spring and the lowest in autumn. The temporal distribution of CO₂ concentrations is mainly affected by photosynthesis, respiration, and heating. The combined effect of terrestrial ecosystems and CO₂ diffusion by wind is responsible for the higher near-surface CO₂ concentration in the northern, western, and southwestern areas of the five Central Asian countries compared to the central, eastern, and southern areas, and energy consumption and wind are the major factors that affect the heterogeneity of the spatial distribution of the CO₂ concentrations in Xinjiang. Full article

In spite of the still increasing number of engineered nanomaterial (ENM) applications, large knowledge gaps exist with respect to their environmental fate, especially after release into air. This review aims to summarize the current knowledge of emissions and behavior of airborne engineered nanomaterials. The whole ENM lifecycle is considered from the perspective of possible releases into the atmosphere. Although in general, emissions during use phase and end-of-life seem to play a minor role compared to entry into soil and water, accidental and continuous emissions into air can occur especially during production and some use cases such as spray application. Implications of ENMs on the atmosphere as e.g., photo-catalytic properties or the production of reactive oxygen species are reviewed as well as the influence of physical processes and chemical reactions on the ENMs. Experimental studies and different modeling approaches regarding atmospheric transformation and removal are summarized. Some information exists especially for ENMs, but many issues can only be addressed by using data from ultrafine particles as a substitute and research on the specific implications of ENMs in the atmosphere is still needed. Full article

During the third China Arctic Research Expedition (July–September 2008), size-resolved measurements of bacteria-containing particles (BCPs) in the marine boundary layer (MBL) air were conducted during a cruise through the East China Sea, the Yellow Sea, the Japan Sea, the Okhotsk Sea, the Bering Sea, the Chukchi Sea, and the Arctic Ocean. The concentrations of total airborne BCPs (TBCPs), non-salt tolerant airborne BCPs (NSBCPs), and salt tolerant airborne BCPs (SBCPs) varied from 29 to 955 CFU m⁻³ (CFU = Colony Forming Unit), 16 to 919 CFU m⁻³, and 4 to 276 CFU m⁻³, with an average value of 275, 182, and 92 CFU m⁻³, respectively. Although the SBCP concentrations were less than the NSBCP concentrations when averaged over all measurements, there are several cases where the reverse is true (e.g., in the high Arctic Ocean). During the cruise, the TBCP sizes were dominated by the diameter >4.7 μm fraction (accounted for 46.3% on average), while the fine fraction (diameter <2.1 μm) accounted for 27.8%. For NSBCPs and SBCPs, the coarse fraction also was the dominant fraction over most regions. The influence of local meteorological conditions on the abundance, size distributions, and species of airborne bacteria is discussed. Notably, in the atmosphere over the Arctic Ocean the abundance of airborne bacteria was apparently related to the distribution of sea ice. As cultivation based methodologies may underestimate the environmental bacterial communities, it is expected that the abundance of bacteria in the ambient air would be higher than that observed in this study. In order to distinguish different species of bacteria, molecular biological techniques (e.g., 16S rDNA analysis) are required for identification in future investigations. Full article

Based on the daily precipitation data from 53 meteorological stations, 11 extreme precipitation indices were selected, categorized and calculated; the temporal and spatial patterns in these indices and their teleconnections with the large-scale circulations were analyzed by the non-parametric Mann-Kendall test; and Sen’s slope estimator and linear regression for the period of 1960–2014 were calculated. The results indicated that all extreme precipitation indices had spatial patterns decreasing from the southeastern to the northwestern parts of the Beijing-Tianjin Sand Source Region (BTSSR), except for the consecutive dry days (CDD), which exhibited a reverse spatial pattern. At the whole-region scale, most extreme precipitation indices showed an insignificant decreasing trend, with exceptions in the intensity indices (RX1day and RX5day) with a statistical significance at the 90% confidence level. The total annual precipitation showed a general shift towards a drier climate in the study area. Spatially, all indices for extreme precipitation showed decreasing trends at most stations, except for simple daily intensity index (SDII) and heavy precipitation days (R10). The change in extreme precipitation may be affected by the El Niño-Southern Oscillation (ENSO), East Asian Summer Monsoon (EASM) and Pacific Decadal Oscillation (PDO). Better understanding of extreme precipitation for the BTSSR may be useful in the regional planning for ecological restoration and water management. Full article

Air pollution is an important public health issue. High levels of carbon monoxide in the atmosphere are hazardous to human health. Studies regarding the concentration of this and other gases in the atmosphere allow political actions to manage and reduce the emission of pollutants. In this context, this paper studied the annual, seasonal, weekly and daily variations of carbon monoxide (CO) concentration for the Metropolitan Region of São Paulo (MRSP). We studied three sites in the MRSP, two of them are located in areas under the influence of heavy vehicle traffic (Osasco and Congonhas) and the third one in a city park (Ibirapuera Park). The results showed high influence of gasoline vehicles on CO emission. In the annual scale, CO concentration decreased due to improvements in emission technology, despite the increasing number of vehicles. CO emission showed a seasonal, weekly and diurnal cycle associated to meteorological conditions and emission patterns. The highest values of mean concentration were observed in June/July for Osasco (2.20 ppm), Congonhas (2.04 ppm) and Ibirapuera (1.04 ppm), during the morning, due to weak dispersion of the polluting gases and higher emission from the rush hours. Full article

The variation of precipitation plays an important role in the eco-hydrological processes and water resources regimes on the Tibetan Plateau (TP). Based on the monthly mean precipitation data of 65 meteorological stations over the TP and surrounding areas from 1961 to 2015, variations, trends and temporal–spatial distribution of precipitation have been studied; furthermore, the possible reasons were also discussed preliminarily. The results show that the annual mean precipitation on the TP was 465.5 mm during 1961–2015. The precipitation in summer (June–August (JJA)) accounted for 60.1% of the whole year’s precipitation, the precipitation in summer half-year (May–October) accounted for 91.0%, while the precipitation in winter half-year (November–April) only accounted for 9.0% of the whole year’s precipitation. During 1961–2015, the annual precipitation trend was 3.8 mm/10a and the seasonal precipitation trends were 3.0 mm/10a, 0.0 mm/10a, −0.1 mm/10a and 0.4 mm/10a in spring, summer, autumn and winter on the TP, respectively. The precipitation has decreased from the southeastern to northwestern TP; the trend of precipitation has decreased with the increase of altitude, but the correlation was not significant. The rising of air temperature and land cover changes may cause the precipitation by changing the hydrological cycle and energy budget. Furthermore, different patterns of atmospheric circulation can also influence precipitation variation in different regions. Full article