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Pyrolysis volatiles and the environmental impact of printing paper in an air atmosphere were investigated using pyrolysis-gas chromatography/mass spectrometry and scanning electron microscopy. CO2 and light-pollution products were found to be the major products from pyrolysis volatiles; furthermore, because oxygen participates in the chemical reaction, many of the pyrolysis volatiles emitted during the paper printing process were different from those formed under an N2 atmosphere. Although a small number of the volatiles were moderately toxic products, the concentrations of these volatiles were low. Heat-induced inkless eco-printing (HIEP) was found to take less time than the pyrolysis experiment in this paper and thus resulted in fewer pyrolysis volatiles. Thus, fewer pyrolysis volatiles will be emitted within the practical temperature range; in particular, no carcinogens were emitted in the pyrolysis temperature range of 250–700 °C. Therefore, HIEP was found to be an ecologically and environmentally preferable technology.

The present study was done to analyze and compare synoptic conditions during the most durable pollution and clean waves (MDPW and MDCW) in Tehran City (capital of Iran). For this purpose, air quality index (AQI) data were first obtained during 2009-2019 from the Tehran Air Quality Control Company in Tehran Province. Then, a threshold of (AQI ≤ 101) representing a polluted and unhealthy atmosphere was considered as MDPW, and a threshold of (AQI ≤ 50) representing a clean (good) air was selected as MDCW in Tehran City by identifying the polluted days. The results showed the presence of MDPW during 43 polluted days from November 21, 2010 to January 2, 2011. Intensity and frequency of the polluted days during statistical period showed a decreasing trend that coincided with an increasing trend of precipitation. Analysis of synoptic conditions occurred during 43 days of MDPW indicated penetration of Siberian high-pressure from the east at sea level and extension of sub-tropical anticyclone in mid-level from the west that led to development of an anticyclone circulation with descending and converging flow in Iran and surrounding region. As a result, a calm and sustainable climate and stable concentration of pollutants were observed throughout Tehran City. Backward trajectory of sources and entry route of the polluted air to Tehran City during peak days of pollution showed that desert regions of southern Iraq and central Iran along the southern and southwestern parts played a major role in increasing concentration of pollutants during occurrence of durable wave. Different routes were observed in entry of dusty and the polluted air to Tehran City according to hybrid single-particle Lagrangian integrated trajectory (HY SPLIT) model, but in most of peak days, the areas that were near and adjacent to Tehran City with height of less than 1000 m played a greater role in particle transport. Investigation of instability indices during MDPW showed that in most days of pollution, values of instability intensity were classified into weak class and lower troposphere (1000-850 hPa) compared to higher levels, and degree of stability and calmness of the atmosphere was more. So that, the highest frequency of temperature inversions occurred near the earth's surface.

For low temperature agricultural crop and meat drying, dryers utilizing the renewable energy source (solar energy) appear to be an efficient technique as it is ecofriendly, energy efficient, and available in free of cost. This work presents the experimental investigation on a solar food dryer equipped with external reflectors to enhance the rate of drying efficiency by removing the moisture content available in the anchovy fish. A comparison of conventional open solar drying is carried out to assess the parameters such as drying efficiency, moisture removal rate, and heat energy required for drying the anchovy fish using the modified solar dryer using the natural convection technique. From the experimental results it is observed that the relative humidity greatly influence the rate of drying. The average relative humidity during the experiments using open solar drying is found as 50–65% whereas, the using solar dryer the average relative humidity inside the chamber is found as 20–35%. The relative humidity of the fish using open solar drying is higher as compared to solar dryer drying as the drying products are kept in open atmosphere. The physical examination results on the dried products proved that using a modified solar dryers, the dried product is free from insects, and dust. Also, it is found that the loss of color from the product is a minimum while compared to conventional open solar drying. The results showed that the thermal efficiency of top tray (dryer 1) and bottom tray (dryer 2) is comparatively higher as compared to that of conventional open solar drying and found as 16.73 and 19.34 %, respectively. Results also showed that nearly 20.05% of the energy could be saved using the modified solar dryer as compared to the open solar drying technique.

In the terrestrial dipolar magnetic field, magnetic circular dichroism (MCD) of UV sunlight by paramagnetic O(2) in an Archean atmosphere (mostly CO(2) and N(2)) results in circular polarization anisotropy (~ 10(−10)). This is used to calculate enantiomeric excess (EE~10(−13)) of glyceraldehyde (3-carbon sugar) with a model that includes racemic production and asymmetric photolysis of its enantiomers. The sign and magnitude of enantiomeric excess (EE) vary with the Earth’s latitude. Unlike random noise fluctuation in spontaneous mirror symmetry breaking (SMSB) models, the sign of EE is deterministic and constant over large areas of prebiotic Earth. The magnitude is several orders greater than the mean amplitude of stochastically fluctuating EE. MCD could provide the initial EE for growth of homochirality by asymmetric autocatalysis.

The aim of this work was to evaluate simultaneously the effect of produced ethanolic biodiesel from several feedstocks (soybean, crambe, macaw, sunflower, and waste cooking oil) and engine operational conditions (low and high engine speed) during combustion of biodiesel/diesel blends on the N2O, NOx, NO, CO2, and CO emission levels in the atmosphere. The biodiesel samples were prepared in one and/or two reaction steps, according to the acid index of each raw material, by esterification using H2SO4 and/or chemical transesterification using sodium ethoxide, both, through ethanolic route. The quality of the produced biodiesels was confirmed by ASTM/EN specifications. Then, biodiesel/diesel blends were prepared according to the following proportions: 10% (B10), 15% (B15), 25% (B25), and 50% (B50). In general way, all raw materials under combustion at low and high engine speed contributed to the formation of NOx and this effect was more drastically increased as the biodiesel concentration in the blends increases. N2O presented a similar behavior except for blends containing crambe and macaw biodiesel whose emissions were slightly reduced as a function of biodiesel content in these blends. Then, Principal component analysis (PCA) was applied to discriminate the effect of engine operating conditions, biodiesel kind, and biodiesel content in the blends during their combustion on the exhaust emissions. The attained results point to crambe and macaw as more environmentally sustainable feedstocks for biodiesel production because they generate less greenhouse gas emissions. These results are particularly attractive considering that, both, crambe and macaw are non-edible feedstocks with great potential for biodiesel production.

Efforts to improve the performance of hydrothermal treatment (HT) in producing high-quality solid fuel from sewage sludge were carried out by elevating reaction pressure and modifying reaction atmosphere. Reaction pressure was varied by injecting N2 at the initial pressures of 0.1, 1.3, and 3.1 MPa, where the N2 was substituted with air or CO2 to vary the reaction atmosphere. The dewatering performance of the treated sludge, heating value of its derived product, and the efficiency of the treatment process were used as examination criteria. Increasing the initial reaction pressure to 1.3 and 3.1 MPa evidently improved dewatering performance as it produced cakes with 2.4 and 4.4% lower moisture content than the cake produced with normal initial reaction pressure. However, the negative effect on higher heating value (HHV) was also prominent as it produced cakes with the lower HHV of 0.7 and 1.7 MJ/kg. The utilization of CO2 as reaction atmosphere leads to the production of cakes with the higher HHV of 0.3–0.5 MJ/kg than the cakes produced under N2 at the same pressure. Moreover, the application of the initial reaction pressure of 1.3 MPa was found as the prime condition since the treatment effectively produced cake with a high effective heating value with a relatively comparable efficiency to the conventional HT at normal initial pressure.

The co-combustion characteristics of municipal sewage sludge and bituminous coal in air and O2/CO2 atmospheres were assessed by using a thermogravimetric analysis approach between heating rates of 20 and 80 K min−1. The combustion characteristics of sewage sludge/bituminous coal blend (50% blending ratio) in air were also compared with its oxy-fuel behavior. In air atmosphere, the ignition temperatures for sludge/coal blends were between those for their parent samples, which ranged from 238 to 418 °C. In O2/CO2 atmosphere with oxygen content of 30%, the ignition temperatures of 50%sewage sludge/50%coal blend were between 260 and 275 °C, which were less than those (268–280 °C) in air. The ignition and burnout indexes of the sample in 30%O2/70%CO2 atmosphere were very close to those in air. The temperatures with respect to maximum combustion rates of the 50%sewage sludge/50%coal blend in 40%O2/60%CO2 were lower than those in air. The average value of the activation energy for the 50%sewage sludge/50%coal blend in 30%O2/70%CO2 was less than that in air.

This paper explores the effects that variation in the coalescence efficiency of the Venus cloud particles can have on the structure of the Venus cloud. It is motivated by the acknowledgment of uncertainties in the measured parameters—and the assumptions made to account for them—that define our present knowledge of the particle characteristics. Specifically, we explore the consequence of allowing the coalescence efficiency of supercooled sulfuric acid in the upper clouds to tend to zero. This produces a cloud that occasionally exhibits an enhancement of small particles at altitude (similar to the upper hazes observed by Pioneer Venus and subsequently shown to be somewhat transient). This simulated cloud occasionally exhibits a rapid growth of particle size near cloud base, exhibiting characteristics similar to those seen in the controversial Mode 3 particles. These results demonstrate that a subset of the variations observed as near-infrared opacity variations in the lower and middle clouds of Venus can be explained by microphysical, in addition to dynamical, variations. Furthermore, the existence of a population of particles exhibiting less efficient coalescence efficiencies would support the likelihood of conditions suitable for charge exchange, hence lightning, in the Venus clouds. We recommend future laboratory studies on the coalescence properties of sulfuric acid under the range of conditions experienced in the Venus clouds. We also recommend future in situ measurements to better characterize the properties of the cloud particles themselves, especially composition and particle habits (shapes).

The combustion behaviors of anthracite coal/spent coffee grounds under oxy-fuel condition were assessed by a thermal analysis technique. At heating rates of 10–40 K min−1, the ignition temperatures and burnout temperatures of all anthracite coal/spent coffee grounds blends decreased with increasing the blending ratios of biomass or oxygen contents in O2/CO2 atmospheres. The ignition temperatures of all samples at the similar oxygen content in oxy-fuel with that of air were higher than that in air atmosphere. In 30 % O2/70 % CO2 atmosphere, the average ignition and comprehensive performance indices of anthracite coal/spent coffee grounds at 40 K min−1 were about 4 times and 18 times more than that at 10 K min−1, respectively. At heating rate of 20 K min−1, the comprehensive performance indices of all samples in 30 % O2/70 % CO2 were very close to those in air. In air and O2/CO2 (21–40 % oxygen contents) atmospheres, the activation energies of release and combustion for volatile matters in the blends ranged from 33.66 to 147.32 kJ mol−1. Activation energies of char combustion in the blends ranged from 21.06 to 109.49 kJ mol−1. There were more significant synergistic effects between anthracite coal and spent coffee grounds during co-combustion in air and oxy-fuel atmospheres at 40 K min−1.

The combustion behaviors of lignite/eucalyptus bark under oxy-fuel condition were assessed based on a thermal analysis technique. The influences of oxygen concentration, heating rates and blending ratios on oxy-fuel combustion performances were revealed, which were compared with those in air. The ignition and comprehensive combustion indices increased with increasing oxygen contents during oxy-fuel combustion. At three heating rates of 10, 15 and 20 K min−1, the average comprehensive performance indices of lignite/eucalyptus bark in 40 %O2/60 %CO2 were about 5–7 times more than those in air. The average comprehensive performance indices of lignite/eucalyptus bark in air were about 2–3 times more than those in O2/CO2 atmosphere at analogous oxygen content. At heating rate of 20 K min−1, the ignition and comprehensive performance indices of lignite/eucalyptus bark in 25 %O2/75 %CO2 were very near to those in air. The combustion kinetics were also evaluated in conjunction with volatile matter and fixed carbon burning periods using Doyle’s and Coats–Redfern’s models. The oxy-fuel combustion kinetics of lignite/eucalyptus bark at oxygen content of 30 % was similar to that in air. There were more significant synergistic effects between lignite and eucalyptus bark during their co-combustion in air and O2/CO2 with oxygen contents of 25 and 30 %.

Ab initio calculations at the G2 level were used in a theoretical description of the kinetics and mechanism of the hydrogen abstraction reactions from fluoro-, chloro- and bromomethane by chlorine atoms. The profiles of the potential energy surfaces show that mechanism of the reactions under investigation is complex and consists of two - in the case of CH3F+Cl - and of three elementary steps for CH3Cl+Cl and CH3Br+Cl. The heights of the energy barrier related to the H-abstraction are of 8–10 kJ mol−1, the lowest value corresponds to CH3Cl+Cl and the highest one to CH3F+Cl. The rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The kinetic equations derived in this study\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \begin{array}{*{20}c} {k\left( {\mathrm{C}{{\mathrm{H}}_3}\mathrm{F}+\mathrm{Cl}} \right)=6.75\times 1{0^{-12 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{2.12 }}\times\exp (-900/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_3}\mathrm{Cl}+\mathrm{Cl}} \right)=6.97\times 1{0^{-12 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.73 }}\times\exp (-795/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_3}\mathrm{Br}+\mathrm{Cl}} \right)=6.26\times 1{0^{-12 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.82 }}\times\exp (-795/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ \end{array} $$\end{document}and\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \begin{array}{*{20}c} {k\left( {\mathrm{C}{{\mathrm{H}}_2}\mathrm{F}+\mathrm{HCl}} \right)=2.88\times 1{0^{-13 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{2.02 }}\times\exp (-1255/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_2}\mathrm{Cl}+\mathrm{HCl}} \right)=2.42\times 1{0^{-13 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.57 }}\times\exp (-2100/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_2}\mathrm{Br}+\mathrm{HCl}} \right)=2.21\times 1{0^{-13 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.69 }}\times\exp (-1485/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ \end{array} $$\end{document}allow a description of the kinetics of the reactions under investigation in the temperature range of 200–3000 K. The kinetics of reactions of the entirely deuterated reactants were also included in the kinetic analysis. Results of ab initio calculations show that D-abstraction process is related with the energy barrier of 5 kJ mol−1 higher than the H-abstraction from the corresponding non-deuterated reactant molecule. The derived analytical equations for the reactions, CD3X+Cl, CH2X+HCl and CD2X+DCl (X = F, Cl and Br) are a substantial supplement of the kinetic data necessary for the description and modeling of the processes of importance in the atmospheric chemistry.

This paper uses a lifecycle analysis to trace the fate of carbon bound in wood products until most of the carbon is released back into the atmosphere. A sensitivity analysis has been carried out to find the effect of change in terminal use (recycling, land filling and burning of discarded products), half-life of wood products and decay rate of carbon in landfills. Of the total carbon harvested from forests in India, about 90% is released into the atmosphere in the first year, due to burning of fuelwood; at the end of 100 years, about 0.8% still remains in the wood products. The sensitivity analysis shows that the length of the lifespan of wood products has only a marginal effect on the amount of carbon sequestered but has significant effect on the amount of carbon in products in use. Thus an important conclusion from this scenario is that by increasing the durability of the wood products, carbon can be locked over a period equal to the time needed to grow the timber for these products. Further, the carbon storage is affected more significantly by the decay rate of carbon in landfills than the proportion of products recycled. The study also shows that wood products can be important stores of carbon, but only if they can substitute for a unit of carbon emitted by burning fossil fuels. Such a lifecycle analysis has the potential to account completely for carbon stock changes in the wood products, where and when they are occurring, and explain how they are occurring.

Birch pollen is one of the main causes of allergy during spring and early summer in northern and central Europe. The aim of this study was to create a forecast model that can accurately predict daily average concentrations of Betula sp. pollen grains in the atmosphere of Szczecin, Poland. In order to achieve this, a novel data analysis technique—artificial neural networks (ANN)—was used. Sampling was carried out using a volumetric spore trap of the Hirst design in Szczecin during 2003–2009. Spearman’s rank correlation analysis revealed that humidity had a strong negative correlation with Betula pollen concentrations. Significant positive correlations were observed for maximum temperature, average temperature, minimum temperature and precipitation. The ANN resulted in multilayer perceptrons 366 8: 2928-7-1:1, time series prediction was of quite high accuracy (SD Ratio between 0.3 and 0.5, R > 0.85). Direct comparison of the observed and calculated values confirmed good performance of the model and its ability to recreate most of the variation.

Refrigerator chill compartments with volumes of 22-L were fabricated, which had different gas tightness properties to gas or water vapor, ranging from 1,770 to 107,000 mL/hr·m2·atm in CO2 permeance at 25°C. Those compartments were filled with prepared fresh vegetables, and then their ability to preserve the quality at 3°C for 14 days was compared. The internal atmosphere and humidity were monitored together with the stored produce quality. The air-tight compartment with the lowest permeance created an atmosphere slightly different from air (CO2 0.8–1.6%; O2 19.7–20.4%), while the other ones had atmospheres of normal air. The relative humidity of the compartments ranged from 52 to 97%. Two air-tight compartments, maintaining a relative humidity mostly higher than 95%, preserved the produce better than the conventional open type one, with reduced weight loss and better retentions of ascorbic acid and chlorophyll.

Dry deposition of gases plays an important role for the deterioration of stone materials and a better understanding of the processes involved will improve our ability to maintain stone monuments and buildings. As a part of an EU-project an investigation with four calcareous stone types have been exposed outdoor at two test sites in Norway for two years. The exposure has been carried out in sheltered position and the amount of reaction products and the penetration depth of SO2 into the stones was determined as soluble sulphate after half a year and after one and two years. Even if most of the sulphate was found in the upper 0.3 mm of the stone, there was an increase in the sulphate content in stone even down to the center of the stone sample. In laboratory tests with SO2, NO2 and changing relative humidity the synergistic effect of NO2 and the importance of the relative humidity was investigated. The uptake rates were calculated from the laboratory studies by analyzing the gas concentrations before and after the exposure chamber. By calculating the deposition velocity from the field study by using the amount of sulphate found in the stones together with the average outdoor concentration of SO2 at the test sites, the values were a magnitude higher than in the laboratory test, highest at the industrial paper mill sites with high concentrations both of SO2 and some hypochlorite and lower in urban atmosphere with fairly low values of SO2 and high values of NO2.

IN view of the interest taken by growers and merchants in England and in South Africa in the possibilities of a new process for the handling of quickly ripening pears in sealed tins or in sealed and punctured tins, the following observations on the behaviour of pears in an atmosphere of nitrogen may be of scientific interest and practical importance.

This paper develops the Möbius strip as an ‘ordering theory’ (Sandberg and Alvesson, 2020) that brings CCT studies into dialogue with mainstream marketing approaches. The aim is to work toward a transdisciplinary understanding of market spatiality, a topic that has become increasingly important for theorists and practitioners (Warnaby and Medway, 2013; Castilhos et al., 2016; Chatzidakis et al., 2018). Building on psychosocial interpretations of the Möbius strip as a ‘tactical’ way of thinking, a range of insights and ideas are organized along a single strip of theorization. This paper maps a continuous plane of logic between the concepts of space, place, emplacement, spatiality, implacement, and displacement. The potential applications of the Möbius strip are then demonstrated by showing how the transdisciplinary topic of ‘atmosphere’ can be theorized from multiple perspectives. The paper concludes by exploring how the Möbius strip might also be employed in other areas of marketing theory and practice, potentially generating further transdisciplinary conversations between CCT and the marketing mainstream.

This paper deals with two well-known problems of ecology and environmental science, global warming and the threat to plant pollination, and their interrelationship. In this paper, a nonlinear mathematical model is proposed and analysed to study the dynamics of plant–pollinator interactions under the adverse effects of increasing environmental temperature due to the increasing concentration of greenhouse gases in the environment. The aim of this paper is also to provide some insights into the problem of global warming and to provide some solutions to the same. Analysis for existence, local stability, and global stability of the interior equilibrium point and uniform persistence of solutions of the system are carried out followed by numerical simulations. Results show that the huge emission of greenhouse gases into the atmosphere, not only reduces plant–pollinator interactions but it may also cause the extinction of the population of pollinators and plants. Results also suggest the immediate reduction of those types of greenhouse gases which cause warming of the environment with higher intensity. Our analysis points out the need for more researches to find out some techniques so that the cooling rate of the environment can be increased.

The aim of this paper is to explore the connection between moods and meteors or atmospheric phenomena in Heidegger’s thinking. The idea of the weather as something affecting our emotional state is not new but goes all the way back to Homer. However, the ontological basis of this connection is missing. In this paper, I argue that Heidegger provides exactly such an ontological account of moods and meteors not as two separate spheres but as a common atmosphere of attuned elementality—a dynamic interface where beings bend into being. Being can no longer be understood solely as that which determines beings qua beings but beings inform/transform being as well. The aim of this paper is to explore the connection between moods and meteors or atmospheric phenomena in Heidegger’s thinking. The idea of the weather as something affecting our emotional state is not new but goes all the way back to Homer. However, the ontological basis of this connection is missing. In this paper, I argue that Heidegger provides exactly such an ontological account of moods and meteors not as two separate spheres but as a common atmosphere of attuned elementality—a dynamic interface where beings bend into being. Being can no longer be understood solely as that which determines beings qua beings but beings inform/transform being as well.

In part I of this paper series, the application of an incomplete adjoint operator to calculate the optimal reduction of the total emissions S′ was suggested. This paper, part II of the series, focuses on calculating the reduction of the anthropogenic emission source S′a As Sc (the source term due to the chemical reaction in the atmosphere) is a complex function of the pollutant concentration ρ, we propose an iterative optimization method using a positive-negative discriminant to obtain S′a from S′. The convergence of the iterations is also proven in this paper.

This paper delineates the process of activation of soot or black carbon particles into cloud droplets over Chennai, India (an Asian megacity). Archaic wood-fired cooking stove emissions from crowded shantytown settlements dispense copious amounts of carbonaceous particles into the city’s atmosphere during morning and evening cooking periods. Traffic emissions also add considerably to the city’s particulate matter loads. At other times, when these sources are reduced (e.g. during non-cooking periods), a pall of residual pollution hovers above the city. This study assesses this problem definitively through process modelling studies undertaken during a typical pre-monsoonal month (October) when the levels of pollution are very high. The novelty of this paper includes a clear quantification of the percentage of activated nuclei resulting from these sources using a sophisticated cloud chemical parcel model. The results show that 85% of the soot and black carbon particles are activated into very small low-lying cloud droplets within Chennai’s boundary layer. We further show for the first time that the presence of these particles results in a slowing down of the auto-conversion process (cloud water to rain droplets). This study could serve as a pointer for other Asian Cities with a sizeable shantytown population in India and elsewhere.

This paper establishes the kinetic equations in atmospheric chemistry that describe the macroscopic mechanisms of secondary fine particle pollution generated by precursors during atmospheric self-purification. The dynamic and static solutions of these equations can be applied to calculate quantitative relationships between the concentration ratio of precursors and secondary fine particles as well as the physical clearance power of the atmosphere, chemical reaction rate, and the scale of a contaminated area. The dynamic solution presented here therefore corresponds with a theoretical formula for calculating the overall rate constant for the oxidation reaction of reducing pollutants in the actual atmosphere based on their local concentrations and meteorological monitoring data. In addition, the static solution presented in this paper reveals the functional relationship between the concentration of secondary fine particles and precursor emission rate as well as atmospheric self-purification capacity. This result can be applied to determine the atmospheric environmental capacity of a precursor. Hourly records collected over the last 40 years from 378 weather stations in mainland China as well as the spatiotemporal distribution sequence of overall oxidation reaction rates from precursors show that when the reference concentration limit of secondary fine particles is 100 μmol m-3, the atmospheric environmental capacity of total precursors can be calculated as 24890×1010 mol yr-1. Thus, when the annual average concentration limit of given fine particles is 35 μg m-3 and the ratio of sulfate and nitrate to 30% and 20% of the total amount of fine particles, the capacities of SO2, NOx and NH3 are 1255, 1344, and 832 (1010g yr-1), respectively. The clearance density of precursors for different return periods across mainland China under above conditions are also provided in this study.

In this paper, a Markov-switching linked autoregressive model is proposed to describe and forecast non-continuous wind direction data. Due to the influence factors of geography and atmosphere, the distribution of wind direction is disjunct and multi-modal. Moreover, for a number of practical situations, wind direction is a time series and its dependence on time provides very important information for modeling. Our model takes these two points into account to give an accurate prediction of this kind of wind direction. A simulation study shows that our model has a significantly higher prediction accuracy and a smaller mean circular prediction error than three existing models and it is illustrated to be effective by analyzing real data. Supplementary materials accompanying this paper appear online.

In this paper, we present a characterization of the optical properties of the aerosols emitted during biomass burning (BB) season in the period 2005–2009. Trends of aerosol optical depth (AOD), Angstrom exponent (α), and precipitable water (PW) were analyzed using a 5-year dataset from AErosol RObotic NETwork (AERONET) observations over Tuxtla Gutierrez (TG), Chiapas. The overall mean AOD (500 nm) during the 2005–2009 period was 0.26 ± 0.18. However, monthly mean values of AOD > 0.5 during the spring months (April and May) would indicate the high load of particles emitted by fires. The overall mean of α (440–870 nm) was 1.40 ± 0.21, which confirms the presence of fine aerosols. Additionally, the combined analysis of the α with its spectral curvature δα, and the results from the spectral de-convolution algorithm (SDA) shows that fine-mode aerosols dominated AOD variability in TG. In this paper, the trajectories of air masses (400 and 1500 m, a.s.l.) arriving at the TG site were classified by using backward trajectory cluster analysis. Trajectory clustering results indicate a BB regional transport from Central America that affects the atmosphere in southeastern Mexico. We use observations of fire radiative power (FRP) from the Moderate Resolution Imaging Spectroradiometer (MODIS) to study the incidence of wildfires and to estimate the BB emissions from 2005 to 2009 in southeastern Mexico. The results indicated a gradual decrease in fires throughout the years. Campeche and Yucatan are the states in southeastern Mexico where BB produces the highest emissions of carbon dioxide (CO2), carbon monoxide (CO), black carbon (BC), and particulate material PM2.5. However, the largest emissions come from wildfires in Guatemala. Finally, to put in context the aerosol optical properties over southeastern Mexico, the sun photometric measurements in TG are compared with those retrieved from AERONET stations located in other tropical biomass burning regions (Brazil and Zambia).

Road transport systems generate toxic particulate matter (PM) when in motion, that ultimately finds its way to the atmosphere. The PM produced by road transport systems can be broadly classified as exhaust and non-exhaust emissions. Exhaust emission is primarily due to product of combustion, as is the case of internal combustion engines and the PM is released to the atmosphere through the tail. Non-exhaust PM sources can be classified as sources such as emissions due to brake wear, tyre wear, road surface wear and resuspension. Both exhaust and non-exhaust sources generate PM of various sizes and shapes that has an impact on our health. Strict legislations by authorities have led to reduced exhaust emissions; however, due to the nature of complexity of PM generation by non-exhaust sources, effective control of non-exhaust emission still needs to be developed. Thus, as exhaust emissions are being controlled, non-exhaust is becoming a significant source of PM emission. The present paper reviews work done by previous researchers on non-exhaust PM and specifically, brake wear from road transport systems as this is one of the most important non-exhaust source of PM in the environment. The finding of the paper would be beneficial to policy makers and researchers.

This paper presents an experimental study on the influence of an oxygen-enriched combustion atmosphere on the process of oxidation. Changing the composition of the oxidizing atmosphere exerts little effect on the oxidation at 800 °C, and CO2 and H2O serves as the primary oxidizing atmosphere in the range of 800–1200 °C. In a high-temperature environment, billets become badly oxidized despite the presence of a certain amount of reducing gas because of the high concentration of CO2 and H2O. This paper also presents the crystal microstructure of steel billet at different temperatures.

More than three decades have passed since the publication of the last review of the Venus clouds and hazes. The paper published in 1983 in the Venus book summarized the discoveries and findings of the US Pioneer Venus and a series of Soviet Venera spacecraft (Esposito et al. in Venus, p. 484, 1983). Due to the emphasis on in-situ investigations from descent probes, those missions established the basic features of the Venus cloud system, its vertical structure, composition and microphysical properties. Since then, significant progress in understanding of the Venus clouds has been achieved due to exploitation of new observation techniques onboard Galileo and Messenger flyby spacecraft and Venus Express and Akatsuki orbiters. They included detailed investigation of the mesospheric hazes in solar and stellar occultation geometry applied in the broad spectral range from UV to thermal IR. Imaging spectroscopy in the near-IR transparency “windows” on the night side opened a new and very effective way of sounding the deep atmosphere. This technique together with near-simultaneous UV imaging enabled comprehensive study of the cloud morphology from the cloud top to its deep layers. Venus Express operated from April 2006 until December 2014 and provided a continuous data set characterizing Venus clouds and hazes over a time span of almost 14 Venus years thus enabling a detailed study of temporal and spatial variability. The polar orbit of Venus Express allowed complete latitudinal coverage. These studies are being complemented by JAXA Akatsuki orbiter that began observations in May 2016. This paper reviews the current status of our knowledge of the Venus cloud system focusing mainly on the results acquired after the Venera, Pioneer Venus and Vega missions.

This paper presents results from measurements of flue gas components and spontaneous emission originated from excited OH-molecules of pulverized coal combustion in air- and CO2/O2−atmospheres. Measurements were conducted for various local oxygen-fuel ratios and O2 contents of the CO2/O2−atmosphere. For this purpose a swirl burner (60kWth) specially designed for oxy-fuel combustion was used. In the present study, measurements in the flame of the swirl burner were performed in a vertical downward fired test furnace. A CCD-camera system was used to capture spontaneous emission of excited OH-molecules. Furthermore, the global flue gas emissions were measured in the stack to gain data for a general description of the combustion process. The measurements were performed for combustion with air and with a premixed oxy-fuel atmosphere. Two different oxy-fuel atmospheres were tested (21 vol.-% O2/ 79 vol.-% CO2 and 25 vol.-% O2/ 75 vol.-% CO2). In addition the oxygen-fuel ratio in the proximity of the burner was varied between 1.0 and 0.6 while the global oxygen-fuel ratio was fixed at 1.3. Global concentrations of CO and NO in the flue gas as well as profiles of the spontaneous emission of OH-molecules are presented and discussed within this paper. Based on these measurements flame structures and flame characteristics are identified.

International audience; This paper deals with the composition and chemical processes occurring in the neutral atmosphere of Venus. Since the last synthesis, observers as well as modellers have emphasised the spatial and temporal variability of minor species, going beyond a static and uniform picture that may have prevailed in the past. The outline of this paper acknowledges this situation and follows closely the different dimensions along which variability in composition can be observed: vertical, latitudinal, longitudinal, temporal. The strong differences between the atmosphere below and above the cloud layers also dictate the structure of this paper. Observational constraints, obtained from both Earth and Venus Express, as well as 1D, 2D and 3D models results obtained since 1997 are also extensively referred and commented by the authors. An non-exhaustive list of topics included follows: modelled and observed latitudinal and vertical profiles of CO and OCS below the clouds of Venus; vertical profiles of CO and SO2 above the clouds as observed by solar occultation and modelled; temporal and spatial variability of sulphur oxides above the clouds. As a conclusion, open questions and topics of interest for further studies are discussed.

This paper investigates patterns of daily evolutions of CO2 in the lower atmosphere at a rural site over 2 years. The first part is devoted to observation analysis using a clustering procedure. However, direct application of the average-linkage method yielded undesirable results. In order to improve this procedure, data were previously processed using three smoothing procedures: the kernel smoothing method, the elliptical procedure, and the second-order cylindrical model. These procedures successfully revealed that clusters were based on daily concentration and range. However, the unequal distribution of frequencies in the clusters proved to be a noticeable disadvantage. Four alternative and simpler schemes for grouping observations were proposed in the second part of this paper. The first, comprising groups following fixed values of daily range and mean concentration, provided a sharp contrast between spring, with a marked daily cycle linked to the biological peak, and summer with a smooth daily cycle and low concentration when the biological minimum was reached. The second scheme is based on isopleth analysis and considers observation groups of similar frequencies following an increasing order of mean concentration and daily range. As a result, seasonal evolution was less marked. Straight lines were the borders for groups in the third scheme, which was similar and simpler than the second. The final scheme divided observations by means of equations of daily range as a quadratic function of daily concentration. The groups formed may be linked to seasons, with the group prevailing in summer presenting a noticeable daily range.

The major tasks of the Baltic Sea Experiment (BALTEX) are to simulate the water and energy cycles of the Baltic Sea catchment and to identify important processes, which are relevant to the climate in the Baltic region. A fully coupled regional climate model system for the Baltic Sea region, called BALTIMOS, was developed in the framework of the German climate research program DEKLIM by linking existing model components for the atmosphere, for the ocean including sea ice, and for hydrology. With this system, it is possible to model the complete water and energy cycles for the Baltic Sea catchment for today’s climate, as well as for the future with climate scenarios. The emphasis in this paper is given to the description of the modelling system and on the comparison of the results of the fully coupled BALTIMOS system against the results of the uncoupled atmospheric component REMO for today’s climate. Both simulations are driven at the atmospheric lateral boundaries with ECMWF analysis data from the European Centre for Medium Range Weather Forecast (ECMWF) for 5 years each. In the uncoupled run, the sea surface temperature (SST) and ice surface temperature (IST) analysed by ECMWF are prescribed, while in the coupled run, SST and IST are provided by the ocean/sea ice model BSIOM. Several analysed parameters are very similar for the land part of the Baltic Sea catchment, while there are differences especially for surface and near-surface temperatures for the fraction of the Baltic Sea itself that indicate further research efforts. As no corrections for the modelled air-sea fluxes are applied for the coupled model system, it is a good result that no drift of the coupled model system is visible in the 5-year integration. The present paper gives an overview about the development of the coupled model system and shows results from first integrations of the system.

Gas explosions or mine fires present the safety threats for coal miners or mine rescues members. For an explosive atmosphere in the underground mine, careful determination of its explosibility status and applying some mitigations to switch an explosive atmosphere into a non-explosive one are very important for any underground rescues or a mine fire extinguishment. However, due to the complicated compositions in an underground sealed atmosphere, accurate determination of the explosibility of such atmosphere status is always a knotty problem for mining engineers. Beside of that, a proper estimation method for the needed time span when an explosive atmosphere is artificially or naturally changed into a non-explosive is also urgently desired. In order to improve the mine safety, this paper is going to address such mentioned problems. The original Coward explosibility diagram is modified with handling the combination effects of different inert gases for more accurate determining the explosibility of an underground sealed atmosphere which consists of complex gas compositions. Then, based on the revised explosibility diagram, a set of mathematical equations are theoretically derived to estimate the inertisation time of a sealed mine atmosphere by using different inerting approaches. Such research efforts can help mine operators understand the risk and provide a tool to control such atmosphere away from dangerous conditions. In order to demonstrate the research findings, at the end of the paper, the explosibility of gas sample taken from a real mine has been analyzed by using the revised Coward diagram. Also, the different inertisation time durations of various mitigation measures for such underground atmosphere have also been calculated.

The damage caused by the asteroid 17–20 metres in diameter that exploded over Chelyabinsk, Russia, on 15 February 2013 is estimated here to have an energy equivalent to about 500 kilotons of TNT. The fireball that streaked across the skies above Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth of information. Two papers in this issue present detailed reconstructions of the Chelyabinsk event. From an analysis of videos, Jiři Borovicka et al. determined the trajectory and velocity of the superbolide with high precision. Its orbit was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), suggesting that the two bodies may be part of the same asteroid family. And they show that it broke into small pieces between the altitudes of 45 and 30 kilometres. In the companion paper, Peter Brown et al. analysed the damage caused by the airburst which they estimate was equivalent in energy to the detonation of 400 to 600 kilotons of TNT. They suggest that the number of impactors with diameters of tens of metres was an order of magnitude higher than current estimates, shifting much of the residual impact risk to these sizes. Most large (over a kilometre in diameter) near-Earth asteroids are now known, but recognition that airbursts (or fireballs resulting from nuclear-weapon-sized detonations of meteoroids in the atmosphere) have the potential to do greater damage1 than previously thought has shifted an increasing portion of the residual impact risk (the risk of impact from an unknown object) to smaller objects2. Above the threshold size of impactor at which the atmosphere absorbs sufficient energy to prevent a ground impact, most of the damage is thought to be caused by the airburst shock wave3, but owing to lack of observations this is uncertain4,5. Here we report an analysis of the damage from the airburst of an asteroid about 19 metres (17 to 20 metres) in diameter southeast of Chelyabinsk, Russia, on 15 February 2013, estimated to have an energy equivalent of approximately 500 (±100) kilotons of trinitrotoluene (TNT, where 1 kiloton of TNT = 4.185×1012 joules). We show that a widely referenced technique4,5,6 of estimating airburst damage does not reproduce the observations, and that the mathematical relations7 based on the effects of nuclear weapons—almost always used with this technique—overestimate blast damage. This suggests that earlier damage estimates5,6 near the threshold impactor size are too high. We performed a global survey of airbursts of a kiloton or more (including Chelyabinsk), and find that the number of impactors with diameters of tens of metres may be an order of magnitude higher than estimates based on other techniques8,9. This suggests a non-equilibrium (if the population were in a long-term collisional steady state the size-frequency distribution would either follow a single power law or there must be a size-dependent bias in other surveys) in the near-Earth asteroid population for objects 10 to 50 metres in diameter, and shifts more of the residual impact risk to these sizes.

This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for naturally occurring CO2 deposits (analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects.

In this paper, we focus on ionospheric absorption in the East Asia sector, and look for manifestations of atmospheric influences in this area. First, a 4-year historical record of absorption measurement at Beijing is presented. This record was obtained by a sweep frequency technique, in which 27-days periodic variation of the absorption level was found to be dominant, appearing in most seasons except winters. Instead, unusual enhancements of the absorption level appeared in winters (winter anomaly), at the meantime the level varied with periods mainly in the range of 8–12 days. Comparing to 27-days period from the Sun, the shorter period oscillations should be related to planetary wave activities in lower atmosphere. Second, fmin data from 5 mid-latitude ionosondes in Japan were used as an indirect but long-term measurement. With the fmin data covering two solar cycles, disturbances with various periods were found to be active around solar maximum years, but the 8–12 days oscillations always existed in winter, showing seasonal dependence instead of connection to solar activity. These results given in this paper demonstrate seasonal and solar cycle-dependent features of the ionospheric absorption in East Asia sector, and confirm the existence of influence from atmosphere-ionosphere coupling in this area, as well as the relationship between ionospheric winter anomaly and planetary wave activity.

Atmospheric gravity wave (AGW) is a typical phenomenon in the upper atmosphere. At mid/low latitudes, climatological sources such as unstable barometric activity in the troposphere play an important role to generate AGWs in the thermosphere. While these sources are also important at high latitudes, energy input from the magnetosphere has additional large contributions to AGW generation. This paper reviews previous studies of AGWs associated with auroral activity at high latitudes. Theoretical studies have indicated that Joule/particle heating and the Lorentz force are major processes for generating AGWs in the thermosphere. Many observations show that AGWs can propagate horizontally for thousands of km from the source region. The paper summarizes equations regarding AGW generation by Joule/particle heating and the Lorentz force, and discusses the relative importance of these two processes.

The atmospheric oxidation degradation of fluorotelomer acrylates (FTAcs) has been proposed as a potential source of perfluorocarboxylic acids (PFCAs) in remote locations. In this paper, detailed reactions of the main oxidant OH radicals with 4:2 FTAc in the atmosphere have been investigated by using density functional theory (DFT) calculation. All possible pathways involved in the oxidation process were presented and discussed. Based on the mechanism, transition state theory (TST) was used to predict the rate constants of the key elementary steps including the initial reactions of OH radical with n:2 FTAcs and the subsequent reactions of the main intermediates. Studies show that the reaction processes of OH radical addition to C = C bond are dominant and the fluorotelomer glyoxylate and formaldehyde are the major products. At 296 K, the calculated overall rate constant of 4:2 FTAc with OH radical is 1.19 × 10

The relationship between the radiance ratio (radiance at wavelength 450 nm to 650 nm) and aerosol optical depth (AOD) is analyzed in this paper by numerical simulation and a “LUT” (look-up table) approach is then presented for the retrieval of AOD from the radiance ratio. In this LUT approach, the AOD retrieval error depends mainly on the assumption of aerosol types. From the preliminary simulation, a typical error of 15%–20% in AOD obtained from the radiance ratio is estimated, due to neglecting changes in the ground albedo and background atmosphere. At its worst, the AOD error reached a maximum of around 50%, which will be refined in the future. In the latter part of the paper, comparisons are made between AOD from the imager and from the CE-318 sun photometer, both located at Xianghe observatory in Hebei Province (39.75°N, 116.96°E). This field experiment shows that AOD from the imager is highly correlated with AOD from the sun photometer, with a correlation coefficient of 0.95 and an average retrieval error of around 7%. A contrast experiment confirms the feasibility of retrieving AOD from all-sky images, but more analysis and future research are required to improve the accuracy.

A method of high resolution periodic signal reconstruction has been developed and implemented into software algorithms. This method, that utilizes a narrow band-pass filter, permits the detection of tidal waves in the atmosphere. Our paper describes and reviews the strength of this method, commonly referred to as the KZFT algorithm. The focus of this paper is given to the recovery of tides in the atmosphere as well as to a discussion of specifics of the reconstruction of these waves. We conclude with several examples regarding the impact of the tidal wave to other atmospheric variables, including wind speed and cloud cover, but details are left for further investigation.

We investigated the interannual variations of the winter stratospheric polar vortex in this paper. EOF analysis shows that two modes of variability dominate the stratospheric polar vortex on interannual timescales. The leading mode (EOF1) reflects the intensity variation of the polar vortex and is characterized by a geopotential height seesaw between the polar region and the mid-latitudes. The second one (EOF2) exhibits variation in the zonal asymmetric part of the polar vortex, which mainly describes the stationary planetary wave activity. As the strongest interannual variation signal in the atmosphere, the QBO has been shown to influence mainly the strength of the polar vortex. On the other hand, the ENSO cycle, as the strongest interannual variation signal in the ocean, has been shown to be mainly associated with the variation of stationary planetary wave activity in the stratosphere. Possible influences of the stratospheric polar vortex on the tropospheric circulation are also discussed in this paper.

Arid and semi-arid areas comprise about 30% of the earth’s surface. Changes in climate and climate variability will likely have a significant impact on these regions. The Loess Plateau over Northwest China is a special semi-arid land surface and part of a dust aerosol source. To improve understanding and capture the direct evidence of the impact of human activity on the semi-arid climate over the Loess Plateau, the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) was established in 2005. SACOL consists of a large set of instruments and focuses on: (1) monitoring of long term tendencies in semiarid climate changes; (2) monitoring of the aerosol effect on the water cycle; (3) studies of interaction between land surface and the atmosphere; (4) improving the land surface and climate models; and (5) validation of space-borne observations. This paper presents a description of SACOL objectives, measurements, and sampling strategies. Preliminary observation results are also reviewed in this paper.

This paper discusses atmospheric ions and their role in aerosol formation. Emphasis is placed upon the upper troposphere where very low temperatures tend to facilitate new particle formation by nucleation. New measurements addressed include: Laboratory measurements of cluster ions, aircraft measurements of ambient atmospheric ions, atmospheric measurements of the powerful nucleating gas H2SO4 and its gaseous precursor SO2. The paper also discusses model simulations of aerosol formation and growth. It is concluded that in the upper troposphere new aerosol formation via ions is a frequent process with relatively large rates. However new particle formation by homogeneous nucleation which does not involve ions also seems to be efficient. The bottleneck in the formation of upper troposphere aerosol particles with sizes sufficiently large to be climate relevant is mostly not nucleation but sufficient growth of new and still very small particles. Our recent upper troposphere SO2 measurements suggest that particle growth by gaseous sulphuric acid condensation can be efficient in certain circumstances. If so, cosmic ray mediated formation of CCN sized particles should at least occasionally be operative in the upper troposphere.

This paper is devoted to a determination of the statistical mean quantities describing spectral line radiation of dynamically active stochastic and multicomponent atmospheres. The lines in LTE are considered so that the effects of multiple scattering can be neglected. Two types of problem are discussed. In the first it is assumed that the realization of one or another type of nonthermal motion depends on the type of structural element and in the other this type of dependence is absent, i.e., it is supposed that the assumed random values of the velocity are distributed according to a law that is common to all the components. Particular attention is paid to a determination of the relative mean square deviation of the intensity of the observed radiation. It appears that the distinctive feature of the relative mean square deviation of the radiation in a line formed in a dynamically active stochastic atmosphere is local “spikes” (maxima) in the wings of the line. The theoretical results in this paper are compared with spectral observations of quiescent solar prominences obtained in framework of the SOHO space mission.

In the previous paper we considered two classic problems - the diffuse reflection of the light beam from semi-infinite atmosphere, and the Milne problem. For both problems we used the technique of invariance principle. In this paper we consider the solution of the problem when in semi-infinite atmosphere the sources of unpolarized radiation are exist. Here we used the technique of the Green matrices. We consider only continuum radiation., Comment: 9 pages. In submission to Astrophysics and Space Science

A large number of papers have been published and great efforts have been made in the recent 20 years by the Chinese oceanographic and meteorological scientists in the ocean-atmosphere interaction studies. The present paper is an overview of the major achievements made by Chinese scientists and their collaborators in studies of larger scale ocean-atmosphere interaction in the following oceans: the South China Sea, the Tropical Pacific, the Indian Ocean and the North Pacific. Many interesting phenomena and dynamic mechanisms have been discovered and studied in these papers. These achievements have improved our understanding of climate variability and have great implications in climate prediction, and thus are highly relevant to the ongoing international Climate Variability and Predictability (CLIVAR) efforts.

During ice storms, ice forms on high voltage electrical lines. This ice formation often results in downed lines and has been responsible for considerable damage to life and property as was evidenced in the catastrophic ice storm of Quebec recently. There are two main aspects, viz., the formation of ice and its timely mitigation. In this paper, we mathematically model the melting of ice due to a higher current applied to the transmission wire. The two dimensional cross-section contains four layers consisting of the transmission wire, water due to melting of ice, ice, and the atmosphere. The model includes heat equations for the various regions with suitable boundary conditions. Heat propagation and ice melting are expressed as a Stefan-like problem for the moving boundary between the layers of ice and water. The model takes into account gravity which leads to downward motion of ice and to forced convection of heat in the water layer. In this paper, the results are applied to the case when the cross-sections are concentric circles to yield melting times for ice dependent on the increase in intensity of the electrical flow in the line.

The paper compares ten different global precipitation data sets over the oceans and discusses their respective strengths and weaknesses in ocean regions where they are potentially important to the salinity and buoyancy budgets of surface waters. Data sets (acronyms of which are given in Section 2) are categorised according to their source of data, which are (1) in situ for Center for Climatic Research (Legates and Willmott, 1990; Archive of Precipitation Version 3.01, http://climate.geog.udel.edu/~climate), Southampton Oceanography Centre (SOC) (Josey et al., J Clim 12:2856–2880, 1999) and University of Wisconsin-Milwaukee (UWM) (Da Silva et al. 1994); (2) satellite for Microwave Sounding Unit (MSU) (Spencer, J Clim 6:1301–1326, 1993), TOPEX (Quartly et al., J Geophys Res 104:31489–31516, 1999), and Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite (HOAPS) (Bauer and Schluessel, J Geophys Res 98:20737–20759, 1993); (3) atmospheric forecast model re-analyses for European Centre for Medium-range Weather Forecast (ECMWF) (Gibson et al. 1997) and National Center for Environmental Prediction (NCEP) (Kalnay et al., Bull Am Meteorol Soc 77:437–471, 1996); and (4) composite for Global Precipitation Climatology Project (GPCP) (satellites and rain gauges, Huffman et al., Bull Am Meteorol Soc 78(1):5–20, 1997) and Climate Prediction Center Merged Analysis of Precipitation (CMAP) (satellites, rain gauges and atmospheric forecast model, Xie and Arkin, Bull Am Meteorol Soc 78(11):2539–2558, 1997). Although there is no absolute field of reference, composite data sets are often considered as the best estimates. First, a qualitative comparison is carried out, which provides for each data set, a description of the geographical distribution of the climatological mean precipitation field. A more careful comparison between data sets is undertaken over periods they have in common. First, six among the ten data sets (SOC, UWM, ECMWF, NCEP, MSU and CMAP) are compared over their common period of 14 years, from 1980 to 1993. Then CMAP is compared to GPCP over the 1988–1995 period and to HOAPS over the 1992–1998 period. Usual diagnostics, like comparison of the precipitation patterns exhibited in the annual climatological means of zonal averages and global budget, are used to investigate differences between the various precipitation fields. In addition, precipitation rates are spatially integrated over 16 regional boxes, which are representative of the major ocean gyres or large-scale ocean circulation patterns. Seasonal and inter-annual variations are studied over these boxes in terms of time series anomalies or correlation coefficients. The analysis attempts to characterise differences and biases according to the original source of data (i.e. in situ or satellite, etc.). Qualitative agreement can be observed in all climatologies, which reproduce the major characteristics of the precipitation patterns over the oceans. However, great disagreements occur in terms of quantitative values and regional patterns, especially in regions of high precipitation. However, a better agreement is generally found in the northern hemisphere. The most significant differences, observed between data sets in the mean seasonal cycles and interannual variations, are discussed. A major result of the paper, which was not expected a priori, is that differences between data sets are much more dependent upon the ocean region that is considered than upon the origin of the data sets (in situ vs satellite vs model, etc.). Our analysis did not provide enough objective elements, which would allow us to clearly recommend a given data set as reference or best estimate. However, composite data sets (GPCP, and especially CMAP), because they never appeared to be really “off” when compared to other data sets, may represent the best recent data set available. CMAP would certainly be our first choice to drive an ocean GCM.

The problem of finding statistical averages which characterize the radiation field in a semi-infinite atmosphere has been discussed by the author in a series of papers. In this paper some of the results obtained there are generalized to media of finite optical thickness. The average number of scattering events undergone by a photon during its random walk in an atmosphere and the average time required for this are determined. Three different types of averages are considered, depending on the photon characteristics over which the averages are taken. Special attention is devoted to the asymptotic behavior of these quantities for media with large optical depths taking the influence of continuum absorption into account.