Seasonal and annual trends of carbonaceous species of PM<Subscript>10</Subscript> over a megacity Delhi,India during 2010–2017

PM₁₀ samples were collected to characterize the seasonal and annual trends of carbonaceous content in PM₁₀ at an urban site of megacity Delhi, India from January 2010 to December 2017. Organic carbon (OC) and elemental carbon (EC) concentrations were quantified by thermal-optical transmission (TOT) method of PM₁₀ samples collected at Delhi. The average concentrations of PM₁₀, OC, EC and TCA (total carbonaceous aerosol) were 222?±?87 (range: 48.2–583.8 μg m^?3), 25.6?±?14.0 (range: 4.2–82.5 μg m^?3), 8.7?±?5.8 (range: 0.8–35.6 μg m^?3) and 54.7?±?30.6 μg m^?3 (range: 8.4–175.2 μg m^?3), respectively during entire sampling period. The average secondary organic carbon (SOC) concentration ranged from 2.5–9.1 μg m^?3 in PM₁₀, accounting from 14 to 28% of total OC mass concentration of PM₁₀. Significant seasonal variations were recorded in concentrations of PM₁₀, OC, EC and TCA with maxima during winter and minima during monsoon seasons. In the present study, the positive linear trend between OC and EC were recorded during winter (R²?=?0.53), summer (R²?=?0.59) and monsoon (R²?=?0.78) seasons. This behaviour suggests the contribution of similar sources and common atmospheric processes in both the fractions. OC/EC weight ratio suggested that vehicular emissions, fossil fuel combustion and biomass burning could be the major sources of carbonaceous aerosols of PM₁₀ at the megacity Delhi, India. Trajectory analysis indicates that the air mass approches to the sampling site is mainly from Indo Gangetic plain (IGP) region (Uttar Pradesh, Haryana and Punjab etc.), Thar desert, Afghanistan, Pakistan and surrounding areas.     

Biogenic hydrogen sulphide emissions and non-sea sulfate aerosols over the Indian Sundarban mangrove forest

Temporal variations in atmospheric hydrogen sulphide concentrations and its biosphere-atmosphere exchanges were studied in the World’s largest mangrove ecosystem, Sundarbans, India. The results were used to understand the possible contribution of H₂S fluxes in the formation of atmospheric aerosol of different size classes (e.g. accumulation, nucleation and coarse mode). The mixing ratio of hydrogen sulphide (H₂S) over the Sundarban mangrove atmosphere was found maximum during the post-monsoon season (October to January) with a mean value of 0.59?±?0.02 ppb and the minimum during pre-monsoon (February to May) with a mean value of 0.26?±?0.01 ppb. This forest acted as a perennial source of H₂S and the sediment-air emission flux ranged between 1213?±?276 μg S m^?2 d^?1(December) and 457?±?114 μg S m^?2 d^?1 (August) with an annual mean of 768?±?240 μg S m^?2d^?1. The total annual emissions of H₂S from the Indian Sundarban were estimated to be 1.2?±?0.6 Tg S. The accumulation mode of aerosols was found to be more enriched with non-sea salt sulfate with an average loading of 5.74 μg m^?3 followed by the coarse mode (5.18 μg m^?3) and nucleation mode (1.18 μg m^?3). However, the relative contribution of Non-sea salt sulfate aerosol to total sulfate aerosol was highest in the nucleation mode (83%) followed by the accumulation (73%) and coarse mode (58%). Significant positive relations between H₂S flux and different modes of NSS indicated the likely link between H₂S, a dominant precursor for the non-sea salt sulfate, and non-sea sulfate aerosol particles. An increase in H₂S emissions from the mangrove could result in an increase in enhanced NSS in aerosol and associated cloud albedo, and a decrease in the amount of incoming solar radiation reaching the Sundarban mangrove forest.     

Ecological limits to terrestrial biological carbon dioxide removal

Terrestrial biological atmospheric carbon dioxide removal (BCDR) through bioenergy with carbon capture and storage (BECS), afforestation/reforestation, and forest and soil management is a family of proposed climate change mitigation strategies. Very high sequestration potentials for these strategies have been reported, but there has been no systematic analysis of the potential ecological limits to and environmental impacts of implementation at the scale relevant to climate change mitigation. In this analysis, we identified site-specific aspects of land, water, nutrients, and habitat that will affect local project-scale carbon sequestration and ecological impacts. Using this framework, we estimated global-scale land and resource requirements for BCDR, implemented at a rate of 1 Pg C y^?1. We estimate that removing 1 Pg C y^?1 via tropical afforestation would require at least 7?×?10⁶ ha y^?1 of land, 0.09 Tg y^?1 of nitrogen, and 0.2 Tg y^?1 of phosphorous, and would increase evapotranspiration from those lands by almost 50 %. Switchgrass BECS would require at least 2?×?10⁸ ha of land (20 times U.S. area currently under bioethanol production) and 20 Tg y^?1 of nitrogen (20 % of global fertilizer nitrogen production), consuming 4?×?10¹²?m³ y^?1 of water. While BCDR promises some direct (climate) and ancillary (restoration, habitat protection) benefits, Pg C-scale implementation may be constrained by ecological factors, and may compromise the ultimate goals of climate change mitigation.     

The vertical distribution of climate forcings and feedbacks from the surface to top of atmosphere

The radiative forcings and feedbacks that determine Earth’s climate sensitivity are typically defined at the top-of-atmosphere (TOA) or tropopause, yet climate sensitivity itself refers to a change in temperature at the surface. In this paper, we describe how TOA radiative perturbations translate into surface temperature changes. It is shown using first principles that radiation changes at the TOA can be equated with the change in energy stored by the oceans and land surface. This ocean and land heat uptake in turn involves an adjustment of the surface radiative and non-radiative energy fluxes, with the latter being comprised of the turbulent exchange of latent and sensible heat between the surface and atmosphere. We employ the radiative kernel technique to decompose TOA radiative feedbacks in the IPCC Fourth Assessment Report climate models into components associated with changes in radiative heating of the atmosphere and of the surface. (We consider the equilibrium response of atmosphere-mixed layer ocean models subjected to an instantaneous doubling of atmospheric CO₂). It is shown that most feedbacks, i.e., the temperature, water vapor and cloud feedbacks, (as well as CO₂ forcing) affect primarily the turbulent energy exchange at the surface rather than the radiative energy exchange. Specifically, the temperature feedback increases the surface turbulent (radiative) energy loss by 2.87 W m^?2 K^?1 (0.60 W m^?2 K^?1) in the multimodel mean; the water vapor feedback decreases the surface turbulent energy loss by 1.07 W m^?2 K^?1 and increases the surface radiative heating by 0.89 W m^?2 K^?1; and the cloud feedback decreases both the turbulent energy loss and the radiative heating at the surface by 0.43 and 0.24 W m^?2 K^?1, respectively. Since changes to the surface turbulent energy exchange are dominated in the global mean sense by changes in surface evaporation, these results serve to highlight the fundamental importance of the global water cycle to Earth’s climate sensitivity.     

Precipitation chemistry and ozone and sulfate concentrations in the ocean atmosphere observed by multi-year cruising in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September

A comprehensive study on the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere was carried out for the data sets in 1990’s. It is important to study the atmospheric situation over the past years as well as the latest, especially in the East Asian region where emission amount of anthropogenic air pollutants have increased year by year due to rapid economic growth. The survey was conducted for 5 years in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September in 1990’s. The purpose of the survey was to study and understand the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere comprehensively in one project. Rainfall over the ocean was insufficiently neutralized. Gas and aerosol over the ocean were mature, i.e., well-mixed, during the period of the transportation. The characteristic latitudinal dependence was observed in the tropospheric ozone concentration, namely, higher in the southern hemisphere and lower in the northern hemisphere (approximately 25 ppb in the 10–40°S region and 5–15 ppb in the 20–40°N region). On the other hand, high concentrations of tropospheric ozone of over 30 ppb were observed in the northern hemisphere, which was attributable to the long-range transportation. The TSP concentration was approximately under the level of 40 μg m^?3 irrespectively of the latitude; in contrast, the nss-SO₄ ^2- concentration showed a clear latitudinal dependence, i.e., higher in the northern hemisphere and lower in the southern hemisphere. The background levels of the nss-SO₄ ^2- concentration were approximately 0.5 μg m^?3 in the 10–40°S region and 2–3 μg m^?3 and 4–5 μg m^?3 in the 0–20°N and 20–40°N regions, respectively.     

Albedo enhancement over land to counteract global warming: impacts on hydrological cycle

A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO₂ leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (?8.2?W?m^?2) to counter global mean radiative forcing from a doubling of CO₂ (3.3?W?m^?2) is approximately twice the forcing needed over the oceans (?4.2?W?m^?2). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification.     

Ambient volatile organic compounds in the atmosphere of industrial central India

Volatile organic compounds (VOCs) are an important group of compounds because of their role in atmospheric chemistry and the risk they pose to human health and ecosystem. Therefore, the interest in determining VOCs in the atmosphere has increased over the last few decades to understand their emission, distribution, and sources. Considering the expanding urbanization and increasing use of fuels, very limited data of VOCs in India is available. This paper describes the chemical analysis of 12 light VOCs in 144 ambient air samples collected from three different sites near Raipur, India during a period of April, 2006-March, 2007 in order to understand their temporal and spatial distributions. This data has provided some important insights into the VOC profile, for the first time, of an industrial area in India. The annual average concentrations of all 12 VOCs in our study ranged from 43.2 to 160.4 μg m^?3 (mean: 95.6?±?31.0). The annual average concentration of individual VOCs in Raipur region ranged from 3.4 μg m^?3 for xylenes to 18.3 μg m^?3 for n-butane. n-Butane, i-butane, and propane were the three most abundant pollutants among all of the VOCs measured. The observed concentrations of these compounds in Raipur region were comparable to other Asian cities with some exceptions. The levels of total VOCs showed seasonal variations with a statistically significant winter maximum and lower values during summer and monsoon ranging from 55.9?±?9.9 μg/m³ in August to 144.5?±?15.5 μg/m³ in January. Sources of these VOCs have been described using species ratios and correlation studies.     

Influence of the atmospheric conditions on PM<Subscript>10</Subscript> concentrations in Poznań, Poland

This study investigates atmospheric conditions’ influence on the mean and extreme characteristics of PM₁₀ concentrations in Poznań during the period 2006–2013. A correlation analysis was carried out to identify the most important meteorological variables influencing the seasonal dynamics of PM₁₀ concentrations. The highest absolute correlation values were obtained for planetary boundary layer height (r = ?0.57), thermal (daily minimum air temperature: r = ?0.51), anemological (average daily wind speed: r = ?0.37), and pluvial (precipitation occurrence: r = ?0.36) conditions, however the highest correlations were observed for temporal autocorrelations (1 day lag: r = 0.70). As regulated by law, extreme events were identified on the basis of daily threshold value i.e. 50 μg m^?3. On average, annually there are approximately 71.3 days anywhere in the city when the threshold value is exceeded, 46.6 % of those occur in winter. Additionally, 83.7 % of these cases have been found to be continuous episodes of a few days, with the longest one persisting for 22 days. The analysis of the macro-scale circulation patterns led to the identification of an easy-to-perceive seasonal relations between atmospheric fields that favour the occurrence of high PM₁₀ concentration, as well as synoptic situations contributing to the rapid air quality improvement. The highest PM₁₀ concentrations are a clear reaction to a decrease in air temperature by over 3 °C, with simultaneous lowering of PBL height, mean wind speed (by around 1 m s^?1) and changing dominant wind directions from western to eastern sectors. In most cases, such a situation is related to the expansion of a high pressure system over eastern Europe and weakening of the Icelandic Low. Usually, air quality conditions improve along with an intensification of westerlies associated with the occurrence of low pressure systems over western and central Europe. Opposite relations are distinguishable in summer, when air quality deterioration is related to the inflow of tropical air masses originating over the Sahara desert.     

Interferometric measurement of ionization in a grassfire

Grassfire plumes are weakly ionized gas. The ionization in the fire plume is due to thermal and chemi-ionization of incumbent species, which may include graphitic carbon, alkalis and thermally excited radicals, e.g., methyl. The presence of alkalis (e.g., potassium and sodium) in the fires makes thermal ionization a predominant electron producing mechanism in the combustion zone. Alkalis have low dissociation and ionization potentials and therefore require little energy to thermally decompose and give electrons. Assuming a Maxwellian velocity distribution of flame particles and electron-neutral collision frequency much higher than plasma frequency, the propagation of radio waves through a grassfire is predicted to have attenuation and phase shift. Radio wave propagation measurements were performed in a moderate intensity (554 kW m^?1) controlled grassfire at 30- and 151-MHz frequencies on a 44 m path using a radio wave interferometer. The maximum temperature measured in the controlled burn was 1071 K and the observed fire depth was 0.9 m. The radio wave interferometer measured attenuation coefficients of 0.033 and 0.054 dB m^?1 for 30- and 151-MHz, respectively. At collision frequency of 1.0 × 10¹¹ s^?1, maximum electron density was determined to be 5.061 × 10¹⁵ m^?3.     

Atmospheric abundance of HULIS during wintertime in Indo-Gangetic Plain: impact of biomass burning emissions

This study reports for the first-time the ambient concentrations of HULIS mass (HULIS-OM, Humic-like substances) and HULIS-C (carbon) in PM₁₀ (particulate matter with aerodynamic diameter?≤?10 μm) from the Indo-Gangetic Plain (IGP at Kanpur, wintertime). HULIS extraction followed by purification and isolation protocol with methanol: acetonitrile (1:1 v/v) on HLB (Hydrophilic-Lipophilic Balanced) cartridge has been established. Quantification of HULIS-C was achieved on a total organic carbon (TOC) analyser whereas HULIS-OM was determined gravimetrically. Consistently high recovery (> 90%) of HULIS-C based on analysis of Humic standard (sodium salt of Humic acid) suggested suitability of our established analytical protocol involving solvent extraction, purification and accurate quantification of HULIS. HULIS-OM varied from 17.3–38 μg m^?3 during daytime and from 19.8–40.6 μg m^?3 during night in this study. During daytime the HULIS-OM constituted 20–30% mass fraction of OM_Total and 10–15% of PM₁₀ mass. However, a relatively low contribution of HULIS-OM has been observed during the night. This observation has been attributed to higher concentrations of OM and PM₁₀ in night owing to nighttime chemical reactivity and condensation of organics in conjunction with shallower planetary boundary layer height. Strong correlation of HULIS-C with K⁺_BB (R²?>?0.80) and significant day-night variability of HULIS-C/WSOC ratio in conjunction with air-mass back trajectories (showing transport of pollutants from upwind IGP) suggest biomass burning emission and secondary transformations as important sources of HULIS over IGP. High-loading of atmospheric PM₁₀ (as high as 440 μg m^?3) with significant contribution of water-soluble organic aerosols (WSOC/OC: ~ 0.40–0.80) during wintertime highlights their plausible potential role in fog and haze formation and their impact on regional-scale atmospheric radiative forcing over the IGP.     

Climate variability of cold surge and its impact on the air quality of Taiwan

Climate change has been receiving wide attention in the last few decades. In order to quantify the climate variability of extreme weather events and their possible impacts on weather parameters and air quality, cold surge events in the past 45 years and the difference in characteristics of air pollutants before and after frontal passage has been examined after December 1993 in Taiwan. The potential impact of climate change on air pollutant concentration and its health implication were presented and discussed. In the past 45 years, the cold surge days (about 18.7 days, or 0.42 day/year) decreased significantly and the average lowest daily temperature for winter in northern Taiwan increased nearly 3°C (0.067°C/year). Based on the definition of cold surge in Taiwan and excluding the stagnation frontal passage, 21 cold surge frontal passage (CSFP) cases and 89 common frontal passage (CFP) events in winter (December–February) were identified in the past 12 years (1993–2005). We take the frontal passage day as the baseline and the differences in air pollutant concentrations and weather-related parameters between the two days before and after the frontal passage days were examined for each case. The averages of the above-mentioned differences during CSFP were compared to the corresponding differences during CFP. During CSFP, the air temperatures after the frontal passage were nearly 4–6°C lower than before the passage at both the background windward stations and urban stations. The average wind speed was about 4–5 m/s higher at the windward stations and less than 2 m/s higher in the major urban areas in Taiwan. During CFP, there was a 2°C increase in temperature but 1 m/s decrease in wind speeds on the day after frontal passage. Because of these meteorological differences, the concentration change of air pollutants during CSFP is significantly greater than that during CFP, especially for PM₁₀ concentration. The difference of PM₁₀ concentration during CSFP can be as large as 20–40 μg/m³ while that during CFP is only about 10 μg/m³. The differences in the other air pollutants such as CO, SO₂, and O₃ during CSFP are greater than those during CFP, but the difference is insignificant. Under the warming trend, less frequent CSFP’s are expected; the impacts on deterioration of air quality and human health are noteworthy.     

Effects of the large-scale atmospheric circulation on the onset and strength of urban heat islands: a case study

Air temperature was monitored at 13 sites across the urban perimeter of a Brazilian midsize city in winter 2011. In this study, we show that the urban heat island (UHI) develops only at night and under certain weather conditions, and its intensity depends not only on the site's land cover but also on the meteorological setting. The urban heat island intensity was largest (6.6 °C) under lingering high-pressure conditions, milder (3.0 °C) under cold anticyclones and almost vanished (1.0 °C) during the passage of cold fronts. The cooling rates were calculated to monitor the growth and decay of the UHI over each specific synoptic setting. Over four contiguous days under the effect of a lingering high-pressure event, we observed that the onset of cooling was always at about 2 h before sunset. The reference site attained mean cooling rate of ?2.6 °C h^?1 at sunset, whilst the maximum urban rate was ?1.2 °C h^?1. Under a 3-day cold anticyclone episode, cooling also started about 2 h before sunset, and the difference between maximum rural (?2.0 °C h^?1) and urban (?1.0 °C h^?1) cooling rates diminished. Under cold-front conditions, the cooling rate was homogeneous for all sites and swang about zero throughout the day. The air temperature has a memory effect under lingering high-pressure conditions which intensified the UHI, in addition to the larger heat storage in the urban area. Cold anticyclone conditions promoted the development of the UHI; however, the cold air pool and relatively light winds smoothed out its intensity. Under the influence of cold fronts, the urban fabric had little effect on the city's air temperature field, and the UHI was imperceptible.     

Photochemical activation of chlorine by iron-oxide aerosol

The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe₂O₃) aerosol particles (mainly hematite, specific surface ~150 m² g^?1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe₂O₃ at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L^?1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8?×?10²¹ atoms cm^?2 h^?1, respectively. In a further series of experiments, the pure Fe₂O₃ aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8?×?10²⁰ Cl atoms cm^?2 h^?1 (at ~4 ppb HCl) to 5?×?10²² Cl atoms cm^?2 h^?1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe₂O₃ experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl.     

Impacts of 21st century climate change on global air pollution-related premature mortality

Climate change modulates surface concentrations of fine particulate matter (PM_2.5) and ozone (O₃), indirectly affecting premature mortality attributed to air pollution. We estimate the change in global premature mortality and years of life lost (YLL) associated with changes in surface O₃ and PM_2.5 over the 21st century as a result of climate change. We use a global coupled chemistry-climate model to simulate current and future climate and the effect of changing climate on air quality. Epidemiological concentration-response relationships are applied to estimate resulting changes in premature mortality and YLL. The effect of climate change on air quality is isolated by holding emissions of air pollutants constant while allowing climate to evolve over the 21st century according to a moderate projection of greenhouse gas emissions (A1B scenario). Resulting changes in 21st century climate alone lead to an increase in simulated PM_2.5 concentrations globally, and to higher (lower) O₃ concentrations over populated (remote) regions. Global annual premature mortality associated with chronic exposure to PM_2.5 increases by approximately 100 thousand deaths (95 % confidence interval, CI, of 66–130 thousand) with corresponding YLL increasing by nearly 900 thousand (95 % CI, 576–1,128 thousand) years. The annual premature mortality due to respiratory disease associated with chronic O₃ exposure increases by +6,300 deaths (95 % CI, 1,600–10,400). This climate penalty indicates that stronger emission controls will be needed in the future to meet current air quality standards and to avoid higher health risks associated with climate change induced worsening of air quality over populated regions.     

Future surface mass balance of the Antarctic ice sheet and its influence on sea level change, simulated by a regional atmospheric climate model

A regional atmospheric climate model with multi-layer snow module (RACMO2) is forced at the lateral boundaries by global climate model (GCM) data to assess the future climate and surface mass balance (SMB) of the Antarctic ice sheet (AIS). Two different GCMs (ECHAM5 until 2100 and HadCM3 until 2200) and two different emission scenarios (A1B and E1) are used as forcing to capture a realistic range in future climate states. Simulated ice sheet averaged 2 m air temperature (T_2m) increases (1.8–3.0 K in 2100 and 2.4–5.3 K in 2200), simultaneously and with the same magnitude as GCM simulated T_2m. The SMB and its components increase in magnitude, as they are directly influenced by the temperature increase. Changes in atmospheric circulation around Antarctica play a minor role in future SMB changes. During the next two centuries, the projected increase in liquid water flux from rainfall and snowmelt, together 60–200 Gt year^?1, will mostly refreeze in the snow pack, so runoff remains small (10–40 Gt year^?1). Sublimation increases by 25–50 %, but remains an order of magnitude smaller than snowfall. The increase in snowfall mainly determines future changes in SMB on the AIS: 6–16 % in 2100 and 8–25 % in 2200. Without any ice dynamical response, this would result in an eustatic sea level drop of 20–43 mm in 2100 and 73–163 mm in 2200, compared to the twentieth century. Averaged over the AIS, a strong relation between $\Updelta$ SMB and $\Updelta\hbox{T}_{2{\rm m}}$ of 98 ± 5 Gt w.e. year^?1 K^?1 is found.     

Climate entropy budget of the HadCM3 atmosphere–ocean general circulation model and of FAMOUS, its low-resolution version

The entropy budget is calculated of the coupled atmosphere–ocean general circulation model HadCM3. Estimates of the different entropy sources and sinks of the climate system are obtained directly from the diabatic heating terms, and an approximate estimate of the planetary entropy production is also provided. The rate of material entropy production of the climate system is found to be ～50 mW m^?2 K^?1, a value intermediate in the range 30–70 mW m^?2 K^?1 previously reported from different models. The largest part of this is due to sensible and latent heat transport (～38 mW m^?2 K^?1). Another 13 mW m^?2 K^?1 is due to dissipation of kinetic energy in the atmosphere by friction and Reynolds stresses. Numerical entropy production in the atmosphere dynamical core is found to be about 0.7 mW m^?2 K^?1. The material entropy production within the ocean due to turbulent mixing is ～1 mW m^?2 K^?1, a very small contribution to the material entropy production of the climate system. The rate of change of entropy of the model climate system is about 1 mW m^?2 K^?1 or less, which is comparable with the typical size of the fluctuations of the entropy sources due to interannual variability, and a more accurate closure of the budget than achieved by previous analyses. Results are similar for FAMOUS, which has a lower spatial resolution but similar formulation to HadCM3, while more substantial differences are found with respect to other models, suggesting that the formulation of the model has an important influence on the climate entropy budget. Since this is the first diagnosis of the entropy budget in a climate model of the type and complexity used for projection of twenty-first century climate change, it would be valuable if similar analyses were carried out for other such models.     

Assessment of surface air warming in northeast China, with emphasis on the impacts of urbanization

Based on homogenized land surface air temperature (SAT) data (derived from China Homogenized Historical Temperature (CHHT) 1.0), the warming trends over Northeast China are detected in this paper, and the impacts of urban heat islands (UHIs) evaluated. Results show that this region is undergoing rapid warming: the trends of annual mean minimum temperature (MMIT), mean temperature (MT), and mean maximum temperature (MMAT) are 0.40 C decade^?1, 0.32 C decade^?1, and 0.23 C decade^?1, respectively. Regional average temperature series built with these networks including and excluding “typical urban stations” are compared for the periods of 1954–2005. Although impacts of UHIs on the absolute annual and seasonal temperature are identified, UHI contributions to the long-term trends are less than 10% of the regional total warming during the period. The large warming trend during the period is due to a regime shift in around 1988, which accounted for about 51% of the regional warming.     

A nocturnal atmospheric loss of CH<Subscript>2</Subscript>I<Subscript>2</Subscript> in the remote marine boundary layer

Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH₂I₂) and chloro-iodomethane (CH₂ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH₂I₂ and CH₂ICl in air and of CH₂I₂ in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH₂I₂ was lower in amplitude than that of CH₂ICl, despite its faster photolysis rate. We speculate that night-time loss of CH₂I₂ occurs due to reaction with NO₃ radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k _CH2I2+NO3 of ≤4 × 10^?13 cm³ molecule^?1 s^?1; a previous kinetic study carried out at ≤100 Torr found k _CH2I2+NO3 of 4 × 10^?13 cm³ molecule^?1 s^?1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/? 0.8 nmol m^?2 d^?1 for CH₂I₂ and 3.7 +/? 0.8 nmol m^?2 d^?1 for CH₂ICl), we show that the model overestimates night-time CH₂I₂ by >60 % but reaches good agreement with the measurements when the CH₂I₂ + NO₃ reaction is included at 2–4 × 10^?13 cm³ molecule^?1 s^?1. We conclude that the reaction has a significant effect on CH₂I₂ and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.     

A numerical study of the influence of urban expansion on monthly climate in dry autumn over the Pearl River Delta, China

Summary In this study, we employed a regional model to simulate the impact of urban expansion on monthly climate in Pearl River Delta (PRD) region. Two experiments were performed by prescribing two different land covers in the PRD region. One land cover represents vegetation in the 1970s which is derived from the United States Geological Survey (USGS) data with 24-category (hereafter referred to as NU). The other land cover represents the current urban condition which is derived from remote sensing data acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) in 2004 (hereafter referred to as HU). Using the two land cover datasets, monthly climate of October 2004 was simulated, which was a very dry season in the PRD region. The results obtained from the numerical simulation show a distinct difference in simulated shelter-level temperature, humidity, surface fluxes and the height of planetary boundary layer (PBL) with two different land cover data sets being specified. The maximum difference in simulated monthly mean temperature over urban areas was 0.9 °C. A large temperature difference was found in urbanized area in Guangzhou, Dongguan, Zhongshan and Shenzhen. The monthly mean relative humidity in urban areas decreased by 1.4% as a result of urban expansion (from 59.2% in NU to 57.8% in HU). The maximum decrease in mixing ratio was 0.4 g/kg in Guangzhou and Dongguan, whereas the maximum decrease in relative humidity was 2.4%. There was an increase of sensible heat flux in developed lands and the maximum increase was 90 W m⁻². In contrast, latent hear flux in urban area decreased and the maximum decrease was 300 W m⁻². In addition, the increase in mean height of PBL ranged from 20 to 80 m (HU compared with NU), and the maximum change of the height was 180 m over urban area in city of Guangzhou.     

Mn(II)-catalysed S(IV) oxidation and its inhibition by acetic acid in acidic aqueous solutions

The kinetics of the S(IV) oxidation by oxygen in the presence of Mn(II) ions and acetic acid has been studied. Experiments were carried out at 25°C, 3.5?≤?pH?≤?5.0, [S(IV)]≈1?×?10^?3 mol/dm³, 1?×?10^?6 mol/dm³?≤?[Mn(II)]?≤?1?×?10^?5 mol/dm³, 1?×?10^?6 mol/dm³?≤?[CH₃COOH]?≤?1?×?10^?4 mol/dm³. Based on the experimental results, rate constants and orders of the reactions were determined. Depending on the reaction conditions, the observed rate constants for the Mn(II)-catalysed S(IV) oxidation ranged between 3.91?×?10^?8 and 8.89?×?10^?7 (mol/dm³) s^?1, and in the presence of acetic acid they ranged between 2.95?×?10^?8 and 7.45?×?10^?7 (mol/dm³) s^?1. The reaction order in S(IV) was zero for both reactions. The effect of Mn(II) ion and acetic acid concentrations as well as an initial pH of the solution on the S(IV) oxidation rate was discussed. It was found that the rate of the S(IV) oxidation depends on the initial pH of the solution but it is independent of the pH change during the reaction. Acetic acid has a weak inhibiting effect on the Mn(II)-catalysed S(IV) oxidation. Under the experimental conditions the S(IV) oxidation rate decreased no more than twice.