An embedding technique to determine ττ backgrounds in proton-proton collision data

An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).Peer reviewe

Performance of missing transverse momentum reconstruction in proton-proton collisions at root s=13 TeV using the CMS detector

The performance of missing transverse momentum ((p) over right arrow (miss)(T)) reconstruction algorithms for the CMS experiment is presented, using proton-proton collisions at a center-of-mass energy of 13 TeV, collected at the CERN LHC in 2016. The data sample corresponds to an integrated luminosity of 35.9 fb(-1). The results include measurements of the scale and resolution of (p) over right arrow (miss)(T), and detailed studies of events identified with anomalous (p) over right arrow (miss)(T). The performance is presented of a (p) over right arrow (miss)(T) reconstruction algorithm that mitigates the effects of multiple proton-proton interactions, using the "pileup per particle identification" method. The performance is shown of an algorithm used to estimate the compatibility of the reconstructed (p) over right arrow (miss)(T) with the hypothesis that it originates from resolution effects.Peer reviewe

Background-like nitrate in desert air

The atmospheric nitrogen cycle is a key process driving the earth&#39;s environmental evolution. Current model studies require knowledge of NOx soil emissions from various land types, but desert emissions remain unquantified or are not addressed with high confidence. Our measurements at two observatories in Taklimakan desert during a dust episode showed an approximately stable and dust-independent nitrate in the air. Its concentration estimated from PM2.5, PM10 and TSP samples under non-dust, floating dust and dust storm conditions was 3.81&plusmn;1.24&mu;gm-3, 2.95&plusmn;0.69&mu;gm-3, 4.99&plusmn;1.71&mu;gm-3, respectively, despite the more-than-one-order difference of dust loading. This concentration was much larger than that in remote marine and tropical forest air. Comprehensive investigation revealed a similar presence of nitrate in other desert air. The nitrate was hypothesized to be the consequence of the conversion of NOx released from desert soils. These results indicate a background-like nitrate and active reactions of nitrogen compounds in desert air.</p

Indoor and Outdoor Chemical Components of PM2.5 in the Rural Areas ofNorthwestern China

A case study of indoor and outdoor fine particles (PM2.5) was undertaken for rural areas in northwestern China, and quantitative data was obtained on their chemical composition including carbon fractions, water soluble ions, and elements. OM (organic matter), sulfate, and geological material dominated PM2.5, followed by nitrate and ammonium, which accounted for 78&ndash;85% of the mass for indoor and outdoor environments. The variations of the carbon fractions indicated that four OC factions and EC1 were more abundant in winter than in summer. SO4 2&minus; contributions were the highest of the ionic species for indoor and outdoor environments (about 40% of total ions in winter and 53% in summer), followed by NO3 &minus; (about 23% in winter and 14% in summer). The integrated results from the ratios of K+/OC, K+/EC, and as well as the EF (enrichment factor) values for K, Cl, S and Pb, indicate that the biofuel contributions were significant in the rural area. The indoor/outdoor ratios and correlations of the components were also investigated. The results for the indoor and outdoor PM2.5 sources showed that biomass burning in summer was the dominant primary source (31% for indoor and 44% for outdoor), and those for winter were coal combustion (21% for indoor and 29% for outdoor) and biomass burning (24% for indoor and 16% for outdoor). Due to the local patterns of energy consumption, the discussion presented in this work could give implications for future strategies to improve rural air quality.</p

The impact of biomass burning on total suspended particulate matter in the southeastern Tibetan Plateau

To investigate the impact of biomass burning (BB) emissions on total suspended particulate (TSP) in the southeastern Tibetan Plateau (TP), BB tracers (including levoglucosan, mannosan, and galactosan) were measured at Lulang (a remote site, &sim;3300 m above sea level) during the period 2015&ndash;2016. The concentrations of levoglucosan and mannosan showed large variability of more than 8-fold (range: 0.029&ndash;0.253 &mu;g m&minus;3) and 6-fold (range: 0.01&ndash;0.061 &mu;g m&minus;3), respectively. The highest seasonal average concentrations of levoglucosan (0.131 &plusmn; 0.073 &mu;g m&minus;3) and mannosan (0.028 &plusmn; 0.019 &mu;g m&minus;3) were observed during the winter season. The BB contributions to the TSP organic carbon (OC) and TSP mass were estimated with positive matrix factorization (PMF) by using BB tracers, inorganic ions, elements, OC, and EC. The BB contributions to the TSP OC and TSP mass were quite substantial in winter with 26% and 14%, respectively. The results evidenced a major contribution of BB to the aerosol OC during winter season. Major potential source distributions of BB were identified, which included the pollution bands along the Indo-Gangetic Plain, the Yarlung Tsangpo River Valley and the interior of the TP. In addition to the long-range transport of BB, the sources of anthropogenic emissions (residential BB for cooking and heating) in the TP may be an important contributor. The results facilitated understanding of the characteristics and effects of BB in the TP.</p

Chemical composition of PM2.5 at a high–altitude regional backgroundsite over Northeast of Tibet Plateau

Aerosol samples were collected from a site near Qinghai Lake (QHL) on the northeastern margin of the Tibetan Plateau (TP) to investigate PM2.5 mass levels and chemical composition, especially their seasonal patterns and sources. The PM2.5 ranged from 5.7 to 149.7&nbsp;&mu;g m&ndash;3, and it was predominately crustal material (-40% on average). The combined mass of eight water&ndash;soluble inorganic ions ranged from 1.0 to 41.5&nbsp;&mu;g m&ndash;3, with the largest contributions from SO42&ndash; NO3-, and Ca2+. Low abundances of organic carbon (OC, range: 1.0 to 8.2&nbsp;&mu;g m&ndash;3) and elemental carbon (EC, 0.2 to 2.3&nbsp;&mu;g m&ndash;3) were found in QHL. Weak seasonality in the OC/EC ratio (4.5&plusmn;2.0) indicated simple and stable sources for carbonaceous particles. The water&ndash;soluble ions, OC and EC accounted for ~30%, 10% and 2% of the PM2.5, respectively. Water&ndash;soluble organic carbon (WSOC, range: 0.5 to 4.3&nbsp;&mu;g m&ndash;3) accounted for 47.8% of the OC. Both OC and WSOC were positively correlated with water&ndash;soluble K+(r=0.70 and 0.73 respectively), an indicator of biomass burning. Higher WSOC and stronger correlations between WSOC and EC in spring and winter compared with summer and autumn are evidence for primary biomass burning aerosols. The concentrations of mass and major compositions were 2&ndash;10 times higher than those for some TP or continental background sites but much lower than urban areas. Compared with particles produced from burning yak dung (a presumptive source material), PM2.5 had higher SO42&ndash;/OC ratios. The higher ratios were presumed as a result of fossil fuel combustion. After excluding data for dust storms events, the relative percentages of OM, EC, K+, NH4+, NO3&ndash; and mineral dust showed little difference among seasons despite different monsoons dominated in four seasons; implying that the PM2.5 sources were relatively stable. The results from QHL evidently reflect regional cha racteristics of the aerosol.</p

Detection and distribution of Tris(2-chloroethyl) phosphate on the East Antarctic ice sheet

Use of PBDEs (Polybrominated Diphenyl Ethers) has been restricted in Europe and North America in recent years. As substitute products with similar properties, OPEs (Organophosphate Esters) are now used as alternatives to PBDEs. Recent research has revealed that, similar to PBDEs, OPEs are also environmentally hazardous like PBDEs. Thus knowledge of their distribution and transport is needed to understand the extent of risk. However, studies on environmental OPEs mainly focus on Europe and North America. Knowledge in the southern hemisphere is very limited. In this study, we analyzed fresh snow samples collected along the transect from Zhongshan Station to Kunlun Station, East Antarctica. Several OPEs were detected in this transect, among which Tris(2-chloroethyl) phosphate (TCEP) had the highest frequency of quantification. It was quantified in most samples from the coastal half of the transect and was detected but not quantified in most samples in the inland half. We show that TCEP at this transect probably originated from the ocean around Antarctica. This study is the first to report the presence of TCEP on the Antarctica ice sheet, providing evidence of its long range transport from the source regions. This work also indicate that TCEP can transport hundreds of kilometers in the Antarctica.</p

Seasonal characteristics of oxalic acid and related SOA in the free troposphere of Mt. Hua, central China: Implications for sources and formation mechanisms

PM10 aerosols from the summit of Mt. Hua (2060 m a.s.l) in central China during the winter and summer of 2009 were analyzed for dicarboxylic acids, ketocarboxylic acids and alpha-dicarbonyls. Molecular composition of dicarboxylic acids (C-2-C-11) in the free tropospheric aerosols reveals that oxalic acid (C-2, 399 +/- 261 ng m(-3) in winter and 522 +/- 261 ng m(-3) in summer) is the most abundant species in both seasons, followed by malonic (C-3) and succinic (C-4) acids, being consistent with that on ground levels. Most of the diacids are more abundant in summer than in winter, but adipic (C-6) and phthalic (Ph) acids are twice lower in summer, suggesting more significant impact of anthropogenic pollution on the wintertime alpine atmosphere. Moreover, glyoxal (Gly) and methylglyoxal (mGly) are also lower in summer (12 +/- 6.1 ng m(-3)) than in winter (22 +/- 13 ng m(-3)). As both dicarbonyls are a major precursor of C-2, their seasonal variation patterns, which are opposite to those of the diacids, indicate that the mountain troposphere is more oxidative in summer. C-2 showed strong linear correlations with levoglucosan in winter and oxidation products of isoprene and monoterpane in summer. PCA analysis further suggested that the wintertime C-2 and related SOA in the Mt Hua troposphere mostly originate from photochemical oxidations of anthropogenic pollutants emitted from biofuel and coal combustion in lowland regions. On contrast, the summertime C-2 and related SOA mostly originate from further oxidation of the mountainous isoprene and monoterpene oxidation products. The AIM model calculation results showed that oxalic acid concentration well correlated with particle acidity (R-2 = 0.60) but not correlated with particle liquid water content, indicating that particle acidity favors the organic acid formation because aqueous-phase C-2 production is the primary mechanism of C-2 formation in ambient aerosols and is driven by acid-catalyzed oxidation.</p

Typical synoptic situations and their impacts on the wintertime airpollution in the Guanzhong basin, China

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 &quot;north-low&quot;, &quot;southwest-trough&quot;, &quot;southeast-high&quot;, &quot;transition&quot;, &quot;southeast-trough&quot;, and &quot;inland-high&quot;. The FLEXPART model has been utilized to demonstrate the corresponding pollutant transport patterns for the typical synoptic situations in the basin. Except for &quot;southwest-trough&quot; and &quot;southeast-high&quot; (defined as favorable synoptic situations), the other 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 2.5aEuro-A mu m) 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 6 days representing the typical synoptic situations during the wintertime of 2013, and the results generally show a good agreement 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, and planetary boundary layer, 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.</p

Black carbon (BC) in a northern Tibetan mountain: effect of Kuwait fires on glaciers

The black carbon (BC) deposition on the ice core at Muztagh Ata Mountain, northern Tibetan Plateau, was analyzed. Two sets of measurements were used in this study, which included the air samplings of BC particles during 2004&ndash;2006 and the ice core drillings of BC deposition during 1986&ndash;1994. Two numerical models were used to analyze the measured data. A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions, and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo. The results show that during 1991&ndash;1992, there was a strong spike in the BC deposition at Muztagh Ata, suggesting that there was an unusual emission in the upward region during this period. This high peak of BC deposition was investigated by using the global chemical transportation model (MOZART-4). The analysis indicated that the emissions from large Kuwait fires at the end of the first Gulf War in 1991 caused this high peak of the BC concentrations and deposition (about 3&ndash;4 times higher than other years) at Muztagh Ata Mountain, suggesting that the upward BC emissions had important impacts on this remote site located on the northern Tibetan Plateau. Thus, there is a need to quantitatively estimate the effect of surrounding emissions on the BC concentrations on the northern Tibetan Plateau. In this study, a sensitivity study with four individual BC emission regions (Central Asia, Europe, the Persian Gulf, and South Asia) was conducted by using the MOZART-4 model. The result suggests that during the &ldquo;normal period&rdquo; (non-Kuwait fires), the largest effect was due to the Central Asia source (44 %) during the Indian monsoon period, while during the non-monsoon period, the largest effect was due to the South Asia source (34 %). The increase in radiative forcing increase (RFI) due to the deposition of BC on snow was estimated by using the radiative transfer model (SNICAR). The results show that under the fresh snow assumption, the estimated increase in RFI ranged from 0.2 to 2.5 W m&minus;2, while under the aged snow assumption, the estimated increase in RFI ranged from 0.9 to 5.7 W m&minus;2. During the Kuwait fires period, the RFI values increased about 2&ndash;5 times higher than in the &ldquo;normal period&rdquo;, suggesting a significant increase for the snow melting on the northern Tibetan Plateau due to this fire event. This result suggests that the variability of BC deposition at Muztagh Ata Mountain provides useful information to study the effect of the upward BC emissions on environmental and climate issues in the northern Tibetan Plateau. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region.</p