Showing papers on "Haze published in 2018"

O-HAZE: A Dehazing Benchmark with Real Hazy and Haze-Free Outdoor Images

Abstract: Haze removal or dehazing is a challenging ill-posed problem that has drawn a significant attention in the last few years. Despite this growing interest, the scientific community is still lacking a reference dataset to evaluate objectively and quantitatively the performance of proposed dehazing methods. The few datasets that are currently considered, both for assessment and training of learning-based dehazing techniques, exclusively rely on synthetic hazy images. To address this limitation, we introduce the first outdoor scenes database (named O-HAZE) composed of pairs of real hazy and corresponding haze-free images. In practice, hazy images have been captured in presence of real haze, generated by professional haze machines, and O-HAZE contains 45 different outdoor scenes depicting the same visual content recorded in haze-free and hazy conditions, under the same illumination parameters. To illustrate its usefulness, O-HAZE is used to compare a representative set of state-of-the-art dehazing techniques, using traditional image quality metrics such as PSNR, SSIM and CIEDE2000. This reveals the limitations of current techniques, and questions some of their underlying assumptions.

I-HAZE: A Dehazing Benchmark with Real Hazy and Haze-Free Indoor Images

Abstract: Image dehazing has become an important computational imaging topic in the recent years. However, due to the lack of ground truth images, the comparison of dehazing methods is not straightforward, nor objective. To overcome this issue we introduce I-HAZE, a new dataset that contains 35 image pairs of hazy and corresponding haze-free (ground-truth) indoor images. Different from most of the existing dehazing databases, hazy images have been generated using real haze produced by a professional haze machine. To ease color calibration and improve the assessment of dehazing algorithms, each scene includes a MacBeth color checker. Moreover, since the images are captured in a controlled environment, both haze-free and hazy images are captured under the same illumination conditions. This represents an important advantage of the I-HAZE dataset that allows us to objectively compare the existing image dehazing techniques using traditional image quality metrics such as PSNR and SSIM.

Aerosol Liquid Water Driven by Anthropogenic Inorganic Salts: Implying Its Key Role in Haze Formation over the North China Plain

Abstract: This study reveals aerosol liquid water content (ALWC) in PM25 ranged from 2% up to 74%, and the associated secondary inorganic fraction rose from 24% to 55%, while ambient relative humidity (RH) increased from 15% to 83% in the atmosphere over Beijing Unexpectedly, the secondary inorganic fraction in PM25 increased with an increase in the ambient RH, which is a meteorological parameter independent of anthropogenic activities, indicating the presence of a feedback mechanism driven by Henry’s law and thermodynamic equilibrium During haze episodes, simultaneously elevated RH levels and anthropogenic secondary inorganic mass concentrations resulted in an abundant ALWC The condensed water could act as an efficient medium for multiphase reactions, thereby facilitating the transformation of reactive gaseous pollutants into particles and accelerating the formation of heavy haze ALWC was well correlated with the mass concentrations of both nitrate and sulfate, indicating both nitrate and sulfate salts play

Review of emissions from smouldering peat fires and their contribution to regional haze episodes

Abstract: Smouldering peat fires, the largest fires on Earth in terms of fuel consumption, are reported in six continents and are responsible for regional haze episodes. Haze is the large-scale accumulation of smoke at low altitudes in the atmosphere. It decreases air quality, disrupts transportation and causes health emergencies. Research on peat emissions and haze is modest at best and many key aspects remain poorly understood. Here, we compile an up-to-date inter-study of peat fire emission factors (EFs) found in the literature both from laboratory and from field studies. Tropical peat fires yield larger EFs for the prominent organic compounds than boreal and temperate peat fires, possibly due to the higher fuel carbon content (56.0 vs 44.2%). In contrast, tropical peat fires present slightly lower EFs for particulate matter with diameter ≤2.5 μm (PM2.5) for unknown reasons but are probably related to combustion dynamics. An analysis of the modified combustion efficiency, a parameter widely used for determining the combustion regime of wildfires, shows it is partially misunderstood and highly sensitive to unknown field variables. This is the first review of the literature on smouldering peat emissions. Our integration of the existing literature allows the identification of existing gaps in knowledge and is expected to accelerate progress towards mitigation strategies.

Nitrate-driven urban haze pollution during summertime over the North China Plain

Abstract: . Compared to the severe winter haze episodes in the North China Plain (NCP), haze pollution during summertime has drawn little public attention. In this study, we present the highly time-resolved chemical composition of submicron particles (PM 1) measured in Beijing and Xinxiang in the NCP region during summertime to evaluate the driving factors of aerosol pollution. During the campaign periods (30 June to 27 July 2015, for Beijing and 8 to 25 June 2017, for Xinxiang), the average PM 1 concentrations were 35.0 and 64.2 µ g m −3 in Beijing and Xinxiang. Pollution episodes characterized with largely enhanced nitrate concentrations were observed at both sites. In contrast to the slightly decreased mass fractions of sulfate, semivolatile oxygenated organic aerosol (SV-OOA), and low-volatility oxygenated organic aerosol (LV-OOA) in PM 1 , nitrate displayed a significantly enhanced contribution with the aggravation of aerosol pollution, highlighting the importance of nitrate formation as the driving force of haze evolution in summer. Rapid nitrate production mainly occurred after midnight, with a higher formation rate than that of sulfate, SV-OOA, or LV-OOA. Based on observation measurements and thermodynamic modeling, high ammonia emissions in the NCP region favored the high nitrate production in summer. Nighttime nitrate formation through heterogeneous hydrolysis of dinitrogen pentoxide (N 2 O 5) enhanced with the development of haze pollution. In addition, air masses from surrounding polluted areas during haze episodes led to more nitrate production. Finally, atmospheric particulate nitrate data acquired by mass spectrometric techniques from various field campaigns in Asia, Europe, and North America uncovered a higher concentration and higher fraction of nitrate present in China. Although measurements in Beijing during different years demonstrate a decline in the nitrate concentration in recent years, the nitrate contribution in PM 1 still remains high. To effectively alleviate particulate matter pollution in summer, our results suggest an urgent need to initiate ammonia emission control measures and further reduce nitrogen oxide emissions over the NCP region.

I-HAZE: a dehazing benchmark with real hazy and haze-free indoor images

Abstract: Image dehazing has become an important computational imaging topic in the recent years. However, due to the lack of ground truth images, the comparison of dehazing methods is not straightforward, nor objective. To overcome this issue we introduce a new dataset -named I-HAZE- that contains 35 image pairs of hazy and corresponding haze-free (ground-truth) indoor images. Different from most of the existing dehazing databases, hazy images have been generated using real haze produced by a professional haze machine. For easy color calibration and improved assessment of dehazing algorithms, each scene include a MacBeth color checker. Moreover, since the images are captured in a controlled environment, both haze-free and hazy images are captured under the same illumination conditions. This represents an important advantage of the I-HAZE dataset that allows us to objectively compare the existing image dehazing techniques using traditional image quality metrics such as PSNR and SSIM.

Haze production rates in super-Earth and mini-Neptune atmosphere experiments

Abstract: Numerous Solar System atmospheres possess photochemically generated hazes, including the characteristic organic hazes of Titan and Pluto. Haze particles substantially impact atmospheric temperature structures and may provide organic material to the surface of a world, potentially affecting its habitability. Observations of exoplanet atmospheres suggest the presence of aerosols, especially in cooler (<800 K), smaller (<0.3× Jupiter’s mass) exoplanets. It remains unclear whether the aerosols muting the spectroscopic features of exoplanet atmospheres are condensate clouds or photochemical hazes1–3, which is difficult to predict from theory alone 4 . Here, we present laboratory haze simulation experiments that probe a broad range of atmospheric parameters relevant to super-Earth- and mini-Neptune-type planets 5 , the most frequently occurring type of planet in our galaxy 6 . It is expected that photochemical haze will play a much greater role in the atmospheres of planets with average temperatures below 1,000 K (ref. 7 ), especially those planets that may have enhanced atmospheric metallicity and/or enhanced C/O ratios, such as super-Earths and Neptune-mass planets8–12. We explored temperatures from 300 to 600 K and a range of atmospheric metallicities (100×, 1,000× and 10,000× solar). All simulated atmospheres produced particles, and the cooler (300 and 400 K) 1,000× solar metallicity (‘H2O-dominated’ and CH4-rich) experiments exhibited haze production rates higher than our standard Titan simulation (~10 mg h–1 versus 7.4 mg h–1 for Titan 13 ). However, the particle production rates varied greatly, with measured rates as low as 0.04 mg h–1 (for the case with 100× solar metallicity at 600 K). Here, we show that we should expect great diversity in haze production rates, as some—but not all—super-Earth and mini-Neptune atmospheres will possess photochemically generated haze. Laboratory experiments explore aerosol formation at conditions that can be found on planets with radii between Earth and Neptune that do not exist in the Solar System but are common elsewhere. Photochemically generated hazes are produced in most cases.

Impact of California Fires on Local and Regional Air Quality: The Role of a Low-Cost Sensor Network and Satellite Observations.

Abstract: PM2.5, or fine particulate matter, is a category of air pollutant consisting of particles with effective aerodynamic diameter equal to or less than 2.5 μm. These particles have been linked to human health impacts as well as regional haze, visibility, and climate change issues. Due to cost and space restrictions, the U.S. Environmental Protection Agency monitoring network remains spatially sparse. To increase the spatial resolution of monitoring, previous studies have used satellite data to estimate ground-level PM concentrations, despite these estimates being associated with moderate to large uncertainties when relating a column measure of aerosol (aerosol optical depth) with surface measurements. To this end, we discuss a low-cost air quality monitor (LCAQM) network deployed in California. In this study, we present an application of LCAQM and satellite data for quantifying the impact of wildfires in California during October 2017. The impacts of fires on PM2.5 concentration at varying temporal (hourly, daily, and weekly) and spatial (local to regional) scales have been evaluated. Comparison between low-cost air quality sensors and reference-grade air quality instruments shows expected performance with moderate to high uncertainties. The LCAQM measurements, in the absence of federal equivalent method data, were also found to be very useful in developing statistical models to convert aerosol optical depth into PM2.5 with performance of satellite-derived PM2.5, similar to that obtained using the federal equivalent method data. This paper also highlights challenges associated with both LCAQM and satellite-based PM2.5 measurements, which require further investigation and research.

Spatial evaluation of Indonesia's 2015 fire-affected area and estimated carbon emissions using Sentinel-1.

Abstract: Fires raged once again across Indonesia in the latter half of 2015, creating a state of emergency due to poisonous smoke and haze across Southeast Asia as well as incurring great financial costs to the government. A strong El Nino-Southern Oscillation (ENSO) led to drought in many parts of Indonesia, resulting in elevated fire occurrence comparable with the previous catastrophic event in 1997/98. Synthetic Aperture Radar (SAR) data promise to provide improved detection of land use and land cover changes in the tropics as compared to methodologies dependent upon cloud and haze free images. This study presents the first spatially explicit estimates of burned area across Sumatra, Kalimantan and West Papua based on high resolution Sentinel-1A SAR imagery. Here we show that 4,604,569 hectares (ha) were burned during the 2015 fire season (overall accuracy 84 %), and compare this with other existing operational burned area products (MCD64, GFED4.0, GFED4.1s). Intersection of burned area with fine-scale land cover and peat layer maps indicates that 0.89 gigatons carbon dioxide equivalents (Gt CO2e) were released through the fire event. This result is compared to other estimates based on non-spatially explicit thermal anomaly measurements or atmospheric monitoring. Using freely available SAR C-band data from the Sentinel mission, we argue that the presented methodology is able to quickly and precisely detect burned areas, supporting improvement in fire control management as well as enhancing accuracy of emissions estimation. This article is protected by copyright. All rights reserved.

The South Asian monsoon-pollution pump and purifier.

Abstract: Air pollution is growing fastest in monsoon-affected South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the wet summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism by which contaminants are rapidly oxidized and deposited to Earth's surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.

Haze Production in the Atmospheres of super-Earths and mini-Neptunes: Insights from the Lab

Abstract: Numerous solar system atmospheres possess aerosols including the characteristic organic hazes of Titan and Pluto. Haze particles substantially impact atmospheric temperatures structures and may provide organic material to the surface of a world, thereby affecting its habitability. Observations of exoplanet atmospheres suggest the presence of aerosols, especially in cooler (<800 K), smaller (<0.3 times Jupiter's mass) exoplanets. It remains unclear if the aerosols muting the spectroscopic features of exoplanet atmospheres are condensate clouds or photochemical hazes, which is difficult to predict from theory alone. We present here the first laboratory haze simulation experiments for atmospheric compositions expected for super-Earths and mini-Neptunes. We explored temperatures from 300 to 600 K and a range of atmospheric metallicities (100x, 1000x, 10000x solar); all simulated atmospheres produced particles, and the cooler (300 and 400 K) 1000x solar metallicity ("H2O-dominated", CH4-rich) experiments exhibited haze production rates higher than our standard Titan simulation (~10 mg/hr versus 7.4 mg/hr for Titan). However the particle production rates varied greatly, with measured rates as low as 0.04 mg/hr (100x solar metallicity, 600 K). Here we show that we should expect some, but not all, super-Earth and mini-Neptune atmospheres to possess a thick photochemically generated haze.

Theoretical transmission spectra of exoplanet atmospheres with hydrocarbon haze: Effect of creation, growth, and settling of haze particles. I. Model description and first results

Abstract: Recently, properties of exoplanet atmospheres have been constrained via multi-wavelength transit observation, which measures an apparent decrease in stellar brightness during planetary transit in front of its host star (called transit depth). Sets of transit depths so far measured at different wavelengths (called transmission spectra) are somewhat diverse: Some show steep spectral slope features in the visible, some contain featureless spectra in the near-infrared, some show distinct features from radiative absorption by gaseous species. These facts infer the existence of haze in the atmospheres especially of warm, relatively low-density super-Earths and mini-Neptunes. Previous studies that addressed theoretical modeling of transmission spectra of hydrogen-dominated atmospheres with haze used some assumed distribution and size of haze particles. In this study, we model the atmospheric chemistry, derive the spatial and size distributions of haze particles by simulating the creation, growth and settling of hydrocarbon haze particles directly, and develop transmission spectrum models of UV-irradiated, solar-abundance atmospheres of close-in warm ($\sim$ 500 K) exoplanets. We find that the haze is distributed in the atmosphere much more broadly than previously assumed and consists of particles of various sizes. We also demonstrate that the observed diversity of transmission spectra can be explained by the difference in the production rate of haze monomers, which is related to the UV irradiation intensity from host stars.

New positive feedback mechanism between boundary layer meteorology and secondary aerosol formation during severe haze events

Abstract: Severe haze events during which particulate matter (PM) increases quickly from tens to hundreds of microgram per cubic meter in 1-2 days frequently occur in China. Although it has been known that PM is influenced by complex interplays among emissions, meteorology, and physical and chemical processes, specific mechanisms remain elusive. Here, a new positive feedback mechanism between planetary boundary layer (PBL), relative humidity (RH), and secondary PM (SPM) formation is proposed based on a comprehensive field experiment and model simulation. The decreased PBL associated with increased PM increases RH by weakening the vertical transport of water vapor; the increased RH in turn enhances the SPM formation through heterogeneous aqueous reactions, which further enhances PM, weakens solar radiation, and decreases PBL height. This positive feedback, together with the PM-Radiation-PBL feedback, constitutes a key mechanism that links PM, radiation, PBL properties (e.g. PBL height and RH), and SPM formation, This mechanism is self-amplifying, leading to faster PM production, accumulation, and more severe haze pollution.

High H2O2 Concentrations Observed during Haze Periods during the Winter in Beijing: Importance of H2O2 Oxidation in Sulfate Formation

Abstract: Atmospheric hydrogen peroxide (H2O2) plays an important role in sulfate formation. To explore the contribution of the H2O2 oxidation pathway to atmospheric sulfate in winter in Beijing, three field campaigns of atmospheric H2O2 measurements were conducted at an urban site (Beijing) and a rural site (Wangdu) during the winter in 2016, 2017, and 2018. The H2O2 concentrations were usually around the detection limit (0.05 ppbv) during clean and severely polluted periods, whereas the highest H2O2 concentration of 0.90 ppbv was observed during moderately polluted periods. Obvious increases in the concentration of H2O2 could be observed after sunset at the urban site during each moderately polluted day, which was mainly attributed to transportation of H2O2-rich air from the rural areas in the south of Beijing. Coincident increases in the concentrations of H2O2 and PM2.5 were also observed during the day at high NO concentrations, implying that heterogeneous reactions might contribute to the formation of H2O2 und...

Decadal surface temperature trends in India based on a new high-resolution data set

Abstract: A new comprehensive surface temperature data set for India is used to document changes in Indian temperature over seven decades, in order to examine the patterns and possible effects of global warming. The data set is subdivided into pre-monsoon, monsoon, and post-monsoon categories in order to study the temperature patterns in each of these periods. When the decade means in maximum, minimum and daily mean temperature for the 2000s are compared to those of the 1950s, a consistent pattern of warming is found over northwestern and southern India, and a pattern of cooling is seen in a broad zone anchored over northeastern India and extending southwestward across central India. These patterns are explained by the presence of a large region of anthropogenic brown haze over India and adjacent ocean regions. These aerosols absorb solar radiation, leading to warming of the haze layer over northeastern and central India and to cooling of the surface air beneath. The heated air rises and then sinks to the north and south of the haze region over northwestern and southern India, warming the air by compression as it sinks in those regions. The possible impact of these temperature patterns on Indian agriculture is considered.

Photochemical Haze Formation in the Atmospheres of Super-Earths and Mini-Neptunes

Abstract: UV (ultraviolet) radiation can induce photochemical processes in the atmospheres of exoplanet and produce haze particles. Recent transmission spectra of super-Earths and mini-Neptunes have demonstrated the possibility that exoplanets have haze/cloud layers at high altitudes in their atmospheres. Haze particles play an important role in planetary atmospheres because they affect the chemistry, dynamics, and radiation flux in planetary atmospheres, and may provide a source of organic material to the surface which may impact the origin or evolution of life. However, very little information is known about photochemical processes in cool, high-metallicity exoplanetary atmospheres. We present here photochemical haze formation in laboratory simulation experiments with UV radiation; we explored temperatures ranging from 300 to 600 degrees Kelvin and a range of atmospheric metallicities (100 times, 1000 times, and 10000 times solar metallicity). We find that photochemical hazes are generated in all simulated atmospheres, but the haze production rates appear to be temperature dependent: the particles produced in each metallicity group decrease as the temperature increases. The images taken with an atomic force microscope (AFM) show that the particle size (15 nanometers to 190 nanometers) varies with temperature and metallicity. Our results provide useful laboratory data on the photochemical haze formation and particle properties, which can serve as critical inputs for exoplanet atmosphere modeling, and guide future observations of exoplanets with the Transiting Exoplanet Survey Satellite (TESS), the James Webb Space Telescope (JWST), and the Wide-Field Infrared Survey Telescope (WFIRST).

Contribution of Hydroxymethane Sulfonate to Ambient Particulate Matter: A Potential Explanation for High Particulate Sulfur During Severe Winter Haze in Beijing

Abstract: PM2.5 during severe winter haze in Beijing, China, has reached levels as high as 880 μg/m, with sulfur compounds contributing significantly to PM2.5 composition. This sulfur has been traditionally assumed to be sulfate, although atmospheric chemistry models are unable to account for such large sulfate enhancements under dim winter conditions. Using a 1-D model, we show that well-characterized but previously overlooked chemistry of aqueous-phase HCHO and S(IV) in cloud droplets to form a S(IV)-HCHO adduct, hydroxymethane sulfonate, may explain high particulate sulfur in wintertime Beijing. We also demonstrate in the laboratory that methods of ion chromatography typically used to measure ambient particulates easily misinterpret hydroxymethane sulfonate as sulfate. Our findings suggest that HCHO and not SO2 has been the limiting factor in many haze events in Beijing and that to reduce severe winter pollution in this region, policymakers may need to address HCHO sources such as transportation. Plain Language Summary Air pollution in Beijing is especially severe in winter, when concentrations of tiny particles in the air can reach concentrations over 20 times greater than the safe level recommended by theWorld Health Organization. In these severe pollution episodes, observations show that a large portion of the particles is made up of sulfur. Scientists have assumed that this sulfur is in the form of sulfate; however, computer simulations of air pollution chemistry have been unable to explain such high sulfate concentrations. We show with a simple computer simulation that a large portion of the sulfur in these haze episodes may, instead of sulfate, actually be a molecule called hydroxymethane sulfonate, which is formed by a chemical reaction in cloud droplets of dissolved formaldehyde with dissolved sulfur dioxide. We also show in laboratory experiments that the machines typically used for determining the chemical composition of particles easily misinterpret hydroxymethane sulfonate as sulfate. Importantly, the chemistry that produces hydroxymethane sulfonate is usually limited by formaldehyde, implying that reductions in sulfur dioxide would be ineffective at reducing severe haze. Instead, focusing future emissions reductions on formaldehyde emissions may be an effective way to curtail severe winter haze in the Beijing area.

Attribution of Anthropogenic Influence on Atmospheric Patterns Conducive to Recent Most Severe Haze Over Eastern China

Abstract: Severe haze pollution in eastern China has caused substantial health impacts and economic loss. Conducive atmospheric conditions are important to affect occurrence of severe haze events, and circulation changes induced by future global climate warming are projected to increase the frequency of such events. However, a potential contribution of an anthropogenic influence to recent most severe haze (December 2015 and January 2013) over eastern China remains unclear. Here we show that the anthropogenic influence, which is estimated by using large ensemble runs with a climate model forced with and without anthropogenic forcings, has already increased the probability of the atmospheric patterns conducive to severe haze by at least 45% in January 2013 and 27% in December 2015, respectively. We further confirm that simulated atmospheric circulation pattern changes induced by anthropogenic influence are driven mainly by increased greenhouse gas emissions. Our results suggest that more strict reductions in pollutant emissions are needed under future anthropogenic warming. Plain Language Summary Extremely severe haze pollution occurred in December 2015 and January 2013 over eastern China with concentrations of PM2.5 reaching 500 μg m . During such severe haze, atmospheric circulation exhibited an anomalous east-west sea level pressure gradient and a weakened East Asia monsoon. We assess in this work the role of anthropogenic climate change in such large-scale circulation anomalies by using a large ensemble of climate simulations forced with and without anthropogenic forcings. Anthropogenic influence is estimated to increase the probability of the occurrence of anomalous atmospheric pattern similar to that in January 2013 (December 2015) by 45% (27%). We further confirm that the simulated anthropogenic circulation changes are induced mainly by increased greenhouse gas emissions. Results from our study suggest that more strict emission reduction measures are needed to improve air quality under a continuing anthropogenic warming in the upcoming decades and global effort to reduce greenhouse gas emissions can decrease the risk of severe haze over eastern China.

Urban haze and photovoltaics

Abstract: Urban haze is a multifaceted threat. Foremost a major health hazard, it also affects the passage of light through the lower atmosphere. In this paper, we present a study addressing the impact of haze on the performance of photovoltaic installations in cities. Using long-term, high resolution field data from Delhi and Singapore we derive an empirical relation between reduction in insolation and fine particulate matter (PM2.5) concentration. This approach enables a straightforward way to estimate air pollution related losses to photovoltaic power generation anywhere on the planet. For Delhi, we find that insolation received by silicon PV panels was reduced by 11.5% ± 1.5% or 200 kWh m−2 per year between 2016 and 2017 due to air pollution. We extended this analysis to 16 more cities around the planet and estimated insolation reductions ranging from 2.0% (Singapore) to 9.1% (Beijing). Using spectrum data from Singapore, we projected how other photovoltaic technologies would be affected and found an additional reduction compared to silicon of between 23% relative for GaAs and 42% for a 1.64 eV perovskite material. Considering current installation targets and local prices for electricity, we project that annual losses in revenue from photovoltaic installations could exceed 20 million USD for Delhi alone, indicating that annual economic damage from air pollution to photovoltaic site operators and investors worldwide could be billions of dollars.