Atmospheric Environment (v.157, #C)

Assessment for the impact of dust events on measles incidence in western China by Yuxia Ma; Jianding Zhou; Sixu Yang; Yuxin Zhao; Xiaodong Zheng (1-9).
Dust events affect human health in both drylands and downwind environments. In this study, we used county-level data during the period of 1965–2005 to assess the impact of dust events on measles incidence in Gansu province in Western China. We used Fast Fourier Transform (FFT) to set up the cyclical regression model; in particular, we set the model to downwind direction for the typical cities in the Hexi Corridor as well as the capital city Lanzhou. The results showed that Spring measles incidence was the highest in the Hexi Corridor, where dust events occur the most frequently over Gansu province. Measles incidence declined on the pathway of dust storms from west to east due to the weakening of both intensity and duration in dust storms. Measles incidence was positively correlated with monthly wind speed and negatively correlated with rainfall amount, relative humidity, and air pressure. Measles incidence was significantly (p ≤ 0.01) positively correlated with daily coarse particles, e.g., TSP and PM10. According to the cyclical regression model, average monthly excess measles that is related to dust events was 39.1 (ranging from 17.3 to 87.6), 149.9 (ranging from 7.1 to 413.4), and 31.3 (ranging from 20.6 to 63.5) in Zhangye, Lanzhou, and Jiuquan, respectively.
Keywords: Dust storm; Measles; Meteorological factors; Fast fourier transform;

Waste Water Treatment Plants are known to have significant emissions of several pollutants and odorants causing nuisance to the near-living population. One of the purposes of the present work is to study a suitable model to evaluate odour emissions from liquid passive area sources. First, the models describing volatilization under a forced convection regime inside a wind tunnel device, which is the sampling device that typically used for sampling on liquid area sources, were investigated. In order to relate the fluid dynamic conditions inside the hood to the open field and inside the hood a thorough study of the models capable of describing the volatilization phenomena of the odorous compounds from liquid pools was performed and several different models were evaluated for the open field emission. By means of experimental tests involving pure liquid acetone and pure liquid butanone, it was verified that the model more suitable to describe precisely the volatilization inside the sampling hood is the model for the emission from a single flat plate in forced convection and laminar regime, with a fluid dynamic boundary layer fully developed and a mass transfer boundary layer not fully developed. The proportionality coefficient for the model was re-evaluated in order to account for the specific characteristics of the adopted wind tunnel device, and then the model was related with the selected model for the open field thereby computing the wind speed at 10 m that would cause the same emission that is estimated from the wind tunnel measurement furthermore, the field of application of the proposed model was clearly defined for the considered models during the project, discussing the two different kinds of compounds commonly found in emissive liquid pools or liquid spills, i.e. gas phase controlled and liquid phase controlled compounds. Lastly, a discussion is presented comparing the presented approach for emission rates recalculation in the field, with other approaches possible, i.e. the ones relying on the recalculation of the wind speed at the emission level, instead of the wind speed that would cause in the open field the same emission that is measured with the hood.
Keywords: Odour emissions; Specific emission rate; Volatilization from liquid pools; Passive area sources; Dispersion modelling;

Association between prenatal exposure to industrial air pollution and onset of early childhood ear infection in China by Qihong Deng; Chan Lu; Yuguo Li; Lv Chen; Yanrong He; Jan Sundell; Dan Norbäck (18-26).
Otitis media (OM) is a common infection in early childhood with repeated attacks that lead to long-term complications and sequelae, but its etiology still remains unclear.To examine the association between early life exposure to air pollution and childhood OM, with the purpose of identifying critical windows of exposure and key components of air pollution in the development of OM.We conducted a prospective cohort study of 1617 children aged 3–4 years in Changsha, China (2011–2012). The prevalence of OM was assessed by a questionnaire administered by the parents. Individual exposures to nitrogen dioxide (NO2), sulfur dioxide (SO2) and particulate matter with an aerodynamic diameter ≤ 10 μm (PM10) during prenatal, postnatal, and current windows were estimated using the measured concentrations at monitoring stations. We used logistic regression model to examine the OM risk in terms of odds ratio (OR) and 95% confidence interval (CI) for exposure to different air pollutants during different timing windows, adjusting for covariates, multi-pollutants, and multi-windows.Life-time prevalence of doctor-diagnosed OM in preschool children in Changsha was 7.3%. Childhood OM was associated only with prenatal exposure to the industrial air pollution with adjusted OR (95% CI) = 1.44 (1.09–1.88) for a 27 μg/m3 increase in SO2, particularly during the first trimester of pregnancy. We further found that prenatal SO2 exposure was not associated with the repeated attacks but was associated with the onset of OM, adjusted OR (95% CI) = 1.47 (1.10–1.96). The association between prenatal SO2 exposure and early childhood OM was robust after adjusting for other pollutants and windows. Sensitivity analysis indicated that the association was stronger in females, children with parental atopy, and children living in houses with cockroaches, new redecoration, and condensation on window pane during winter.We provide new evidence that prenatal exposure to industrial air pollution is associated with early childhood OM in China and may contribute to the onset of childhood OM. Our findings are helpful in developing more effective preventative strategies for childhood OM.Display Omitted
Keywords: Air pollution; Ear infection; Otitis media; Pregnancy; Sulfur dioxide; Infection; Trimester;

Hazardous gas leaks in the atmosphere can cause significant economic losses in addition to environmental hazards, such as fires and explosions. A three-stage hazardous gas leak source localization method was developed that uses movable and stationary gas concentration sensors. The method calculates a preliminary source inversion with a modified genetic algorithm (MGA) and has the potential to crossover with eliminated individuals from the population, following the selection of the best candidate. The method then determines a search zone using Markov Chain Monte Carlo (MCMC) sampling, utilizing a partial evaluation strategy. The leak source is then accurately localized using a modified guaranteed convergence particle swarm optimization algorithm with several bad-performing individuals, following selection of the most successful individual with dynamic updates. The first two stages are based on data collected by motionless sensors, and the last stage is based on data from movable robots with sensors. The measurement error adaptability and the effect of the leak source location were analyzed. The test results showed that this three-stage localization process can localize a leak source within 1.0 m of the source for different leak source locations, with measurement error standard deviation smaller than 2.0.
Keywords: Source inversion; Hazardous gas leak; Genetic algorithm; Markov Chain Monte Carlo; Particle swarm optimization;

Photochemical reaction between triclosan and nitrous acid in the atmospheric aqueous environment by Jianzhong Ma; Chengzhu Zhu; Jun Lu; Yu Lei; Jizhong Wang; Tianhu Chen (38-48).
Nitrous acid (HONO) is an important tropospheric pollutant and a major source of hydroxyl radical in the atmospheric gas phase. However, studies on the role of HONO in atmospheric aqueous phase chemistry processes are relatively few. The present work investigated the photochemical reaction of HONO with triclosan (TCS), which is an emerging contaminant, using a combination of laser flash photolysis spectrometry and gas chromatography mass spectrometry. With these techniques, the reaction pathway of HONO with TCS was proposed by directly monitoring the transient species and detecting the stable products. ·OH was generated from the photodissociation of the HONO aqueous solution and attacked TCS molecules on different sites to produce the TCS-OH adducts with a second-order rate constant of 1.11 × 109 L mol−1 s−1. The ·OH added a C atom adjacent to the ether bond in the aromatic ring of TCS and self-decayed when the ether bond broke. The intermediates generated from the addition of ·OH to the benzene ring of the TCS molecular structure were immediately nitrated by HONO, which played a key role in the formation process of nitrocompounds. An atmospheric model suggests that the aqueous oxidation of TCS by ·OH is a major reaction at high liquid water concentrations, and the photolysis of TCS dominates under low-humidity conditions.Display Omitted
Keywords: Laser flash photolysis; Triclosan; Nitrous acid; Atmospheric aqueous-phase; Transient absorption;

Woodchip is widely used as fuel in dedicated biomass and, even in some conventional energy generation plants. However, there are concerns about atmospheric air pollution from flue gases emitted during wood biomass combustion, particularly oxides of nitrogen (NO x ) and particulates <10 μm diameter (PM10). In the United Kingdom (UK) a small scale biomass heat generation support scheme, the Renewable Heat Incentive (RHI), has been introduced. Qualifying criteria for this scheme have included limits for flue gas emissions of NO X and PM10 of 150 and 30 g per gigajoule (g/GJ) of energy input, respectively. In an experiment, three locally available types of Willow (Salix spp) and one of Sitka spruce (Picea sitchensis) woodchips, showed significant differences in physical and chemical constituents, gaseous and particulate emissions. During combustion in a 120 kW biomass system, air flows, flue gas temperatures and energy output correlated with gaseous emissions, NO x with raw fuel ash, nitrogen, phosphorus and potassium content, as did all flue gas particulate fractions. PM10 ranged from 30.3 to 105.7 g/GJ and NO x from 91.2 to 174.3 g/GJ. Sitka spruce produced significantly lower emissions of PM10 and NOx (27.5 and 52.6% less, respectively) than the three willow fuels, from which emissions were above the RHI emissions limits.
Keywords: Particulates; Gaseous emissions; Combustion; Woodchip; Willows;

Organic aerosols over Indo-Gangetic Plain: Sources, distributions and climatic implications by Nandita Singh; Alaa Mhawish; Karine Deboudt; R.S. Singh; Tirthankar Banerjee (59-74).
Organic aerosol (OA) constitutes a dominant fraction of airborne particulates over Indo-Gangetic Plain (IGP) especially during post-monsoon and winter. Its exposure has been associated with adverse health effects while there are evidences of its interference with Earth's radiation balance and cloud condensation (CC), resulting possible alteration of hydrological cycle. Therefore, presence and effects of OA directly link it with food security and thereby, sustainability issues. In these contexts, atmospheric chemistry involving formation, volatility and aging of primary OA (POA) and secondary OA (SOA) have been reviewed with specific reference to IGP. Systematic reviews on science of OA sources, evolution and climate perturbations are presented with databases collected from 82 publications available throughout IGP till 2016. Both gaseous and aqueous phase chemical reactions were studied in terms of their potential to form SOA. Efforts were made to recognize the regional variation of OA, its chemical constituents and sources throughout IGP and inferences were made on its possible impacts on regional air quality. Mass fractions of OA to airborne particulate showed spatial variation likewise in Lahore (37 and 44% in fine and coarse fractions, respectively), Patiala (28 and 37%), Delhi (25 and 38%), Kanpur (24 and 30%), Kolkata (11 and 21%) and Dhaka. Source apportionment studies indicate biomass burning, coal combustion and vehicular emissions as predominant OA sources. However, sources represent considerable seasonal variations with dominance of gasoline and diesel emissions during summer and coal and biomass based emissions during winter and post-monsoon. Crop residue burning over upper-IGP was also frequently held responsible for massive OA emission, mostly characterized by its hygroscopic nature, thus having potential to act as CC nuclei. Conclusively, climatic implication of particulate bound OA has been discussed in terms of its interaction with radiation balance.Display OmittedLarge heterogeneities of organic aerosol were reported throughout IGP with characteristic variations in compositions and climate implications.
Keywords: Organic aerosol; Biomass; Climate change; CCN; PAHs; Indo-Gangetic plain; Trans-boundary;

Effectiveness of temporary control measures for lowering PM2.5 pollution in Beijing and the implications by Yong Wang; Yifeng Xue; Hezhong Tian; Jian Gao; Ying Chen; Chuanyong Zhu; Huanjia Liu; Kun Wang; Shenbing Hua; Shuhan Liu; Panyang Shao (75-83).
In order to investigate the effects of the temporary strengthening of air quality assurance controlling measures during the Beijing 2015 IAAF World Championships and the Military Parade Assurance Period (MPAP) in China, we collected daily PM2.5 aerosol samples at three typical sites (urban downtown, suburban and rural background area, respectively) in Beijing and investigated the variations of concentration of the water-soluble ions, elemental constituents, organic carbon (OC) and elemental carbon (EC) in PM2.5 from Aug.15 to Sept.10, 2015. Simultaneously, 1-h high-resolution continuous monitoring results of PM2.5 mass concentration as well as the chemical components which were measured at another online monitoring urban site were incorporated. The concentrations of PM2.5 and other gaseous pollutants (SO2, NO2 and CO) during the parade control period (Aug.20-Sept.3) exhibited a substantially decrease compared with the concentrations during both the non-control (August 15 to August 19 and September 4 to September 10) period and the same period in 2014. According to the CMC results, the major components were identified as secondary inorganic aerosol (SIA, the combination of sulfate, ammonium and nitrate), mineral dust and particular organic matter (POM), which together accounted for more than 80% of PM2.5 in urban and suburban sites. POM is found to account for the largest proportion, and the obviously higher proportion of POM in the urban area revealed the significance contribution from vehicles. Compared with the non-control period, the mass concentrations of SIA and secondary organic carbon (SOC) decreased obviously. However, SIA and SOC are observed to play an important role in contributing to the rapid growth process of PM2.5 under unfavorable meteorological conditions during the control period. In view of the gradual improvement of air quality in Beijing, as well as the contribution of secondary aerosol formations in total PM2.5, effective control of primary gaseous pollutants and volatile organic compounds (VOCs) will be very significant for further lowering the concentration of PM2.5 in Beijing in normal time.Display Omitted
Keywords: Parade blue; Chemical composition; Positive matrix factorization; Chemical mass closure; Secondary aerosols; Enhanced control measures;

Characterizing CH4, CO2 and N2O emission from barn feeding Tibetan sheep in Tibetan alpine pastoral area in cold season by Tianwei Xu; Na Zhao; Linyong Hu; Shixiao Xu; Hongjin Liu; Li Ma; Xinquan Zhao (84-90).
Herein, methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) emission from different aged barn feeding Tibetan sheep were characterized using a respiration chamber in combination with gas chromatograph method in cold season of 2013. This work was based on measuring the increase of gas concentration inside respiration chamber by the means of gas chromatograph. Results indicated that diurnal CH4 emission patterns for barn feeding Tibetan sheep were driven by feeding schedule, diurnal CO2 emission patterns were relatively stable with two slight emission peaks, diurnal N2O emission patterns were driven by the variation of temperature inside chamber. Diurnal CH4 emission rates were 17.65, 19.49 and 21.06 g sheep−1 d−1 for yearling, two-year and three-year barn feeding Tibetan sheep, account for 6.15%, 5.76% and 5.45% of their daily gross energy intakes, respectively. Diurnal CO2 emission rates were 526.88, 588.43 and 640.66 g sheep−1 d−1 for yearling, two-year and three-year barn feeding Tibetan sheep, respectively. Diurnal N2O emission rates were 1.64, 1.25 and 1.05 mg sheep−1 d−1 for yearling, two-year and three-year barn feeding Tibetan sheep, respectively. Three-year barn feeding Tibetan sheep released more CO2-eq on per unit BW and BW0.75 gain basis.
Keywords: Tibetan sheep; Methane; Carbon dioxide; Nitrous oxide; Diurnal emission patterns; Tibetan alpine pastoral area;

Analysis of the characteristics of single atmospheric particles in Chengdu using single particle mass spectrometry by Junke Zhang; Bin Luo; Jianqiang Zhang; Feng Ouyang; Hongyi Song; Peichuan Liu; Pan Cao; Klaus Schäfer; Shigong Wang; Xiaojuan Huang; Yongfu Lin (91-100).
Chengdu, the capital of Sichuan Province and the main city in Sichuan basin, is one of the heavily polluted cities in China. The characteristics of single particles in the atmosphere over Chengdu are critical for the in-depth understanding of their sources, formation mechanisms, and effects. In this study, a continuous ambient aerosol measurement was performed in summer in Chengdu with a single particle aerosol mass spectrometer (SPAMS) and other monitoring instruments. The particulate matter (PM) mass concentrations were low during our study period: PM2.5 and PM10 (aerosol particles with an aerodynamic diameter of less than 2.5 or 10 μm) were 40.5 ± 23.6 μg m−3 and 67.0 ± 38.1 μg m−3, respectively. This was mainly caused by the favorable meteorological conditions during the summer season. Twelve particle types were identified and classified as dust particles (Dust), four types of carbonaceous particles, organic nitrogen and potassium containing particles (KCN), four types of secondary particles, Na-K-containing particles (NaK), and metal-containing particles (Metal). The highest contribution of particles was from potassium with elemental carbon (KEC; 23.0%), and the lowest from elemental carbon (EC; 0.2%). All types of particles showed different diurnal variations and size distributions, which were closely related to their sources and reactions in the atmosphere. The eastern and southern air masses corresponded with high PM2.5 mass concentrations. The contributions of KEC and K-sulfate (KSO4) particles to PM2.5 were clearly higher than those in air masses from the southeast. During polluted days, the contributions of KEC and KSO4 particles increased, while the contributions of organic carbon (OC), combined OC and EC particles (OCEC), and K-nitrate (KNO3) particles decreased. This shows the importance of biomass burning and industrial emissions for the PM2.5 pollution in Chengdu. These results will be useful for the in-depth understanding of the PM2.5 pollution in Chengdu, even in Sichuan basin.
Keywords: Single particles; Single particle aerosol mass spectrometer (SPAMS); Chemical composition; Chengdu;

Variability of airborne bacteria in an urban Mediterranean area (Thessaloniki, Greece) by Savvas Genitsaris; Natassa Stefanidou; Matina Katsiapi; Konstantinos A. Kormas; Ulrich Sommer; Maria Moustaka-Gouni (101-110).
The abundance, biomass and the taxonomic composition of the total airborne bacterial communities in a coastal urban area of Northeastern Mediterranean Sea were examined. In total, 27 air samples were collected across three seasons from a sampling point of approximately 30 m altitude in the center of the city. The abundance and biomass were determined with the use of epifluorescent microscopy, while the taxonomic composition was characterized by next-generation sequencing methods. Overall, the highest values of bacterial abundance were recorded during summer, with values exceeding abundances recorded in other urban sites across Europe, reaching 41 × 104 cells m−3. Out of 6 core meteorological parameters, only air temperature was found to significantly affect the abundance and biomass of airborne bacteria. Concerning the taxonomic composition of the airborne bacterial community, the group of Proteobacteria was the most diverse, with 47% of the total number of OTUs belonging to them, followed by Firmicutes, Actinobacteria and Bacteroidetes. The most dominant OTU belonged to γ-Proteobacteria, and was closely affiliated to Pseudomonas sp., a taxon commonly found to actively participate in the formation of ice-nuclei in the atmosphere. Finally, 19 OTUs were shared between all seasons and were found to be among the most dominant overall. The majority of these OTUs were affiliated to genera from soil and wastewater origin, while several were affiliated to genera that include known or opportunistic pathogens. Yet, only rare OTUs were affiliated to taxa with possible marine origin (e.g. Synechococcus sp.). The results showed that the atmosphere of the study area harbors a diverse and abundant bacterial community.
Keywords: Biodiversity; Pyrosequencing; 16S rRNA gene; Prokaryotes; Bioaerosols; Coastal;

Effects of warming and nitrogen fertilization on GHG flux in the permafrost region of an alpine meadow by Xiaopeng Chen; Genxu Wang; Tao Zhang; Tianxu Mao; Da Wei; Zhaoyong Hu; Chunlin Song (111-124).
The limited number of in situ measurements of greenhouse gas (GHG) flux during soil freeze-thaw cycles in permafrost regions limits our ability to accurately predict how the alpine ecosystem carbon sink or source function will vary under future warming and increased nitrogen (N) deposition. An alpine meadow in the permafrost region of the Qinghai-Tibet Plateau was selected, and a simulated warming with N fertilization experiment was carried out to investigate the key GHG fluxes (ecosystem respiration [Re], CH4 and N2O) in the early (EG), mid (MG) and late (LG) growing seasons. The results showed that: (i) warming (4.5 °C) increased the average seasonal Re, CH4 uptake and N2O emission by 73.5%, 65.9% and 431.6%, respectively. N fertilization (4 g N m−2) alone had no significant effect on GHG flux; the interaction of warming and N fertilization enhanced CH4 uptake by 10.3% and N2O emissions by 27.2% than warming, while there was no significant effect on the Re; (ii) the average seasonal fluxes of Re, CH4 and N2O were MG > LG > EG, and Re and CH4 uptake were most sensitive to the soil freezing process instead of soil thawing process; (iii) surface soil temperature was the main driving factor of the Re and CH4 fluxes, and the N2O flux was mainly affected by daily rainfall; (iv) in the growing season, warming increased greenhouse warming potential (GWP) of the alpine meadow by 74.5%, the N fertilization decreased GWP of the warming plots by 13.9% but it was not statistically significant. These results indicate that (i) relative to future climate warming (or permafrost thawing), there could be a hysteresis of GHG flux in the alpine meadow of permafrost region; (ii) under the scenario of climate warming, increasing N deposition has limited impacts on the feedback of GHG flux of the alpine meadow.
Keywords: Simulated warming; Nitrogen addition; Greenhouse gas; Freeze-thaw cycles;

Photooxidation of cyclohexanone in simulated atmosphere: A potential source of atmospheric formic acid by Aparajeo Chattopadhyay; Koushik Mondal; Monoj Samanta; Tapas Chakraborty (125-134).
Gas phase photooxidation of cyclohexanone (CH) has been studied in the laboratory in a simulated atmospheric environment (synthetic air, 1 bar pressure) under the exposure of 311 nm UV light. Formic acid along with formaldehyde and ethylene are identified as the major photooxidation products. Quantum yield for the production of these species is measured and the values are compared with previous studies on the photo dissociation of CH. For 6 h of light irradiation with initial CH concentration of 9.19 ± 0.1 × 1016 molecules cm−3, the measured quantum yield values of ethylene and formaldehyde, the two primary photooxidation products, are 0.0395 ± 0.001 and 0.0028 ± 0.002, respectively. These values are comparable with CH dissociation quantum yield, 0.24 ± 0.02, and also the quantum yield of CO production, 0.0940 ± 0.001. The energetic parameters of different steps of the proposed reaction mechanism are calculated by electronic structure theory method at DFT/B3LYP/6–311++G** level. A reaction modeling has been performed, and similarity in simulated quantum yield values with that of the experimentally measured ones validates the suggested reaction mechanism. Experimentally measured values of rate constants of most of the elementary reaction steps incorporated in the modeling are not known, and the calculated values, obtained by use of CVT and RRKM theoretical methods are used. The total yield of formic acid, which has been assigned as a secondary oxidation product, is 3.46 ± 0.25 × 1015 molecules cm−3 as obtained from experiment and this data matches well with the value of 2.67 × 1015 molecules cm−3 obtained from reaction modeling for 6 h of UV irradiation. The yield of formic acid is comparable with the yield of primary photo products. The results imply that photooxidation of CH and analogous compounds might have significant contributions to production of formic acid in the earth's troposphere. According to the prediction of the modeling results presented here, the contribution of cyclohexanone photooxidation to the atmospheric concentration of formic acid is ∼1 pptv.Display Omitted
Keywords: Photochemistry; Photooxidation; Atmospheric chemistry; Reaction kinetics; Kinetic simulation;

Exposure to fine particulate, black carbon, and particle number concentration in transportation microenvironments by R. Morales Betancourt; B. Galvis; S. Balachandran; J.P. Ramos-Bonilla; O.L. Sarmiento; S.M. Gallo-Murcia; Y. Contreras (135-145).
This research determined intake dose of fine particulate matter (PM2.5), equivalent black carbon ( e BC ), and number of sub-micron particles ( N p ) for commuters in Bogotá, Colombia. Doses were estimated through measurements of exposure concentration, a surrogate of physical activity, as well as travel times and speeds. Impacts of travel mode, traffic load, and street configuration on dose and exposure were explored. Three road segments were selected because of their different traffic loads and composition, and dissimilar street configuration. The transport modes considered include active modes (walking and cycling) and motorized modes (bus, car, taxi, and motorcycle). Measurements were performed simultaneously in the available modes at each road segment. High average e BC concentrations were observed throughout the campaign, ranging from 20 to 120 μ g m − 3 . Commuters in motorized modes experienced significantly higher exposure concentrations than pedestrians and bicyclists. The highest average concentrations of PM2.5, e BC , and N p were measured inside the city's Bus Rapid Transit (BRT) system vehicles. Pedestrians and bicycle users in an open street configuration were exposed to the lowest average concentrations of PM2.5 and e BC , six times lower than those experienced by commuters using the BRT in the same street segment. Pedestrians experienced the highest particulate matter intake dose in the road segments studied, despite being exposed to lower concentrations than commuters in motorized modes. Average potential dose of PM2.5 and e BC per unit length traveled were nearly three times higher for pedestrians in a street canyon configuration compared to commuters in public transport. Slower travel speed and elevated inhalation rates dominate PM dose for pedestrians. The presence of dedicated bike lanes on sidewalks has a significant impact on reducing the exposure concentration for bicyclists compared to those riding in mixed traffic lanes. This study proposes a simple method to perform loading effect correction for measurements of black carbon using multiple portable aethalometers.
Keywords: Fine particulate; Black carbon; Pollution in urban microenvironments in latin-America; Ultrafine particles; Micro-aethalometer loading correction;

Some studies have shown that low-molecular-weight VOCs such as ethylene and acetylene can form SOA. However, so far propylene (C3H6) has not been studied. The current work systematically investigates irradiations of propylene in the presence of NOx (x = 1, 2) in a self-made indoor chamber. Only a small amount of secondary organic aerosols (SOA) was formed under 5% and 80% RH conditions without sodium chloride (NaCl) seed particles or in the presence of solid NaCl. When NaCl was in the form of droplets, liquid water content (LWC) increased from 34.5 to 169.8 μg m−3 under different initial NaCl concentrations, and correspondingly the amount of SOA linearly increased from 5.9 to 29.8 μg m−3 (SOA = 0.0164 × LWC+1.137, R2 = 0.97) at the C3H6/NOx ratio of 32.2–44.9 (ppbC/ppb). The initial C3H6/NOx concentration ratio considerably impacted the formation of SOA, in which the amount of SOA increased from 12.1 to 47.9 μg m−3 exponentially as the ratio decreased from 46.5 to 6.3 with an important point of the ratio value of 11. At the ratio of less than 11 in the regime under the control of C3H6, SOA concentrations decreased considerably with increasing ratio, whereas at the ratio value of larger than 11 in the NOx controlled regime, SOA slightly decreased with increasing ratio. From combination of the analysis of different functional groups of particles by IR spectra and ESI-Exactive-Orbitrap mass spectrometer, the constituents of SOA were identified to be hydroperoxides (e.g. HOCH2CCl(CH3)OOH), esters (e.g. CH2ClC(O)OCHClCHO), organic nitrates (e.g. HO2CH(CH2Cl)C(O)OCCl(CH2Cl)C(O)OCHClCH2ONO2), etc. Furthermore, a liquid-phase mechanism of SOA formation has been proposed in this study.
Keywords: Propylene; Secondary organic aerosols; Liquid water content; Ratio of C3H6/NOx;

Straw incorporation is a common agricultural practice, but the additional carbon source may increase greenhouse gas emissions by stimulating microbial activity in soil, particularly when straw is applied at the same time as nitrogen (N) fertilizer. We investigated the coupled effects of straw and N fertilizer on greenhouse gas emissions in a rainfed winter wheat–summer fallow system in Northwest China. Simultaneous applications of straw and N fertilizer increased N2O emissions by up to 88%, net greenhouse gas (NGHG) emission and net greenhouse gas intensity (NGHGI) by over 90%, and the N2O emission factor by over 2-fold. When straw was applied before N fertilizer, the emission factor (0.22%) decreased by approximately one-half compared with that for simultaneous applications (0.45%). In addition, early straw incorporation decreased N2O emissions, NGHG, and NGHGI by 35% (0.62 kg N2O-N ha−1 yr−1), 40% (242 kg CO2-eq ha−1 yr−1), and 38% (42 kg CO2-eq t−1 grain), respectively. We identified the period 30–35 days after N fertilization as a crucial period for evaluating the effectiveness of management practices on N2O emissions. The time between straw and fertilizer applications was negatively related to N2O emission (R2 = 0.8031; p < 0.01) but positively related to soil CH4 uptake (R2 = 0.7662; p < 0.01). Therefore, early straw incorporation can effectively mitigate greenhouse gas emissions by reducing N2O flux and increasing soil CH4 uptake without significantly decreasing grain yield.
Keywords: Coupled effects; Early straw incorporation; N2O emission; CH4 uptake; CEP;

Corrigendum to ‘Mortality and air pollution in Beijing: The long-term relationship’ [Atmospheric Environment 150C (2017) 238–243] by Guiqian Tang; Pusheng Zhao; Yinghong Wang; Wenkang Gao; Mengtian Cheng; Jinyuan Xin; Xin Li; Yuesi Wang (167).