Haze Conditions Research Articles

Springtime Arctic haze contributions of submicron organic particles from European and Asian combustion sources

[1] The composition of Arctic aerosol, especially during the springtime Arctic haze, may play an important role in the radiative balance of the Arctic. The contribution of organic components to Arctic haze has only recently been investigated. Because measurements in this region are sparse, little is known about organic particle composition, sources, and concentrations. This study compares springtime measurements in the Arctic regions north of the Atlantic (ICEALOT, 2008) and Pacific (Barrow, Alaska, 2008 and 2009) oceans. The aerosol organic functional group composition from Fourier transform infrared (FTIR) spectroscopy combined with positive matrix factorization (PMF) and elemental tracer analysis indicate that mixed combustion sources account for more than 60% (>0.3 μg m−3) of the submicron organic mass (OM1) for springtime haze conditions in both regions. Correlations with typical combustion tracers (S, Zn, K, Br, V) provide evidence for the contribution of combustion sources to the Arctic OM1. However, the two regions are influenced by different urban and industrial centers with different fuel usage. High-sulfur coal burning in northeastern Europe impacts the northern Atlantic Arctic region, while oil burning and forest fires in northeastern Asia and Alaska impact the northern Pacific Arctic region. Quadrupole and High Resolution Aerosol Mass Spectrometry measurements confirm the highly oxygenated nature of the OM1, with an oxygenated organic aerosol (OOA) spectrum from PMF. High co-emissions of sulfate and organics from coal-burning in northeastern Europe produce significant concentrations of organosulfate functional groups that account for 10% of OM1 measured by FTIR spectroscopy during ICEALOT. These observations provide preliminary support for a heterogeneous mechanism of organosulfate formation on acidic sulfate particles.

The wavelength dependent model of extinction in fog and haze for free space optical communication

The wavelength dependence of the extinction coefficient in fog and haze is investigated using Mie single scattering theory. It is shown that the effective radius of drop size distribution determines the slope of the log-log dependence of the extinction on wavelengths in the interval between 0.2 and 2 microns. The relation between the atmospheric visibility and the effective radius is derived from the empirical relationship of liquid water content and extinction. Based on these results, the model of the relationship between visibility and the extinction coefficient with different effective radii for fog and for haze conditions is proposed.

Size-resolved hygroscopicity of submicrometer urban aerosols in Shanghai during wintertime

Information about the hygroscopic growth factors and mixing state is important for understanding the haze formation mechanism in the highly polluted Yangtze River Delta. Herein, the size-resolved hygroscopicity of ambient aerosols in Shanghai was studied during wintertime. The hygroscopic growth factors were measured using a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) for dry particles with diameters of 30–250 nm on the campus of Fudan University. A modal external mixture containing two hygroscopic groups was observed. The mean hygroscopic growth factors of the less-hygroscopic group at 85% relative humidity were lower than 1.10, and the average number fraction of the less-hygroscopic group varied in the range of 0.33–0.17, decreasing slightly with the increase of dry particle size. The mean hygroscopic growth factors of the more-hygroscopic group showed there was a significant difference between Aitken and accumulation mode particles, nearly 1.3 for Aitken mode particles and above 1.4 for accumulation mode particles. On the basis of the ammonium sulfate model, the average hygroscopic volume fraction of the more-hygroscopic particles was estimated to be in the range of 0.47–0.70, and there was a large gap between the hygroscopic volume fractions of Aitken and accumulation mode particles. The hygroscopic growth against relative humidity test not only showed that deliquescence relative humidity depended on particle size, but also revealed that the addition of nitrate on the particles was initially promoted by sulfate condensation. The results also suggested that most accumulation mode particles were deliquesced under haze conditions.

Aerosol optical properties of regional background atmosphere in Northeast China

Aerosol optical properties from 2005 to 2008 at the Longfengshan regional background station in Northeast China were measured and analyzed. The annual mean of aerosol optical depth (AOD) at 440 nm for the four years was about 0.27 ± 0.25, 0.39 ± 0.37, 0.35 ± 0.34, and 0.38 ± 0.38, respectively, and the corresponding annual mean for the Angstrom exponent between 440 nm and 870 nm was about 1.43 ± 0.48, 1.23 ± 0.37, 1.53 ± 0.47, and 1.55 ± 0.42. The average monthly AOD 440nm showed similar seasonal variation with a maximum in spring and a minimum in autumn. The monthly means of AOD at 440, 675, 870 and 1020 nm increase from the January to March with the maxima about 0.77 ± 0.04, 0.65 ± 0.04, 0.58 ± 0.06, 0.57 ± 0.07, respectively and decrease from September to February with the minima about 0.32 ± 0.12, 0.22 ± 0.09, 0.15 ± 0.08, and 0.13 ± 0.07 in January. The monthly mean of Angstrom exponent shows a minimum in March (0.97 ± 0.52) and a maximum in September (1.66 ± 0.29). Both the AOD and Angstrom exponent presents single peak distributions of occurrence frequencies. The Longfenshan data showed high AODs (>1.00) both clustering in the fine mode growth wing and the coarse mode. Two typical cases under dust and haze conditions showed that the AOD under dusty day decreased from 2.20 to 1.20 and the Angstrom exponent increased from 0.10 to 1.00. On the contrast, the AOD under haze day remained relatively stable about 0.90 and the Angstrom exponent was around 1.40. The 3-day backtrajectory analysis at Longfengshan illustrated that the air-masses near ground on the dust day were from Bohai Sea and passed through Liaodong Peninsula and Northeast plain in China. But the air-masses on 500 m AGL were originated from western Mongolia and crossed Gobi deserts, Otindag Sand Land and Horqin Sand Land in Northeast China. The air-masses at Longfengshan near ground 500 m and 1000 m AGL on the haze days were from North China Region and passed through Northeast Heavy Industrial Base in Northeast China.

Haze episodes at Syowa Station, coastal Antarctica: Where did they come from?

During our aerosol measurement program at Syowa Station, Antarctica, in 2004–2007, some low‐visibility (haze) phenomena were observed during winter–spring under conditions with low winds and without drifting snow and fog. During “Antarctic haze” phenomena, the number concentration of aerosol particles and black carbon concentration increased by 1 to 2 orders higher relative to background conditions at Syowa Station, whereas surface O3 concentration dropped simultaneously, especially after polar sunrise. Chemical analysis showed that major aerosol constituents in the haze phenomena were sea salt (e.g., Na+, Cl−). Trajectory analysis and the Navy Aerosol Analysis and Prediction System model showed that plumes from biomass burning in South America and southern Africa were transported to Syowa Station, on the Antarctic coast, because of the eastward (occasionally westward) approach of cyclones in the Southern Ocean and subsequent poleward flow. This poleward flow from midlatitudes of the plume and injection of sea‐salt particles during the transport might engender Antarctic haze phenomena at Syowa Station. Differences of O3 concentration between the background and the haze conditions tended to be larger in spring (after polar sunrise) than in winter. Enhancement of sea‐salt particles in the haze events can serve important roles in providing additional sources of reactive halogen species.

A Volumetric Approach to Change Detection in Satellite Images

The increasing availability of very high resolution satellite imagery has spurred interest in automatically detecting very fine detailed changes in an area over time, a particularly useful tool for analyzing activity in dense urban areas. However, attempting automated change detection at this resolution is difficult due to the motion parallax of elevated structures. This paper presents a comprehensive solution to change detection in areas of significant 3D relief using a new framework called volumetric appearance modeling (VAM). This approach can manage the complications of unknown and changing world surfaces by maintaining a 3D voxel-based model, where probability distributions for surface occupancy and image appearance are stored in each voxel. These distributions are continuously updated as new images are received using an adaptive learning procedure. This representation is demonstrated to produce accurate change detection results under conditions of variable illumination and viewpoint as well as haze conditions present in satellite imagery. The volumetric representation also supports automatic sensor model correction to align incoming imagery to a common geographic reference. This registration approach is demonstrated to achieve geo-positioning accuracy on the order of the ground sampling distance (GSD) or better.

Revised Algorithm for Estimating Light Extinction from IMPROVE Particle Speciation Data

The Interagency Monitoring of Protected Visual Environments (IMPROVE) particle monitoring network consists of approximately 160 sites at which fine particulate matter (PM2.5) mass and major species concentrations and course particulate matter (PM10) mass concentrations are determined by analysis of 24-hr duration sampling conducted on a 1-day-in-3 schedule. A simple algorithm to estimate light extinction from the measured species concentrations was incorporated in the 1999 Regional Haze Rule as the basis for the haze metric used to track haze trends. A revised algorithm was developed that is more consistent with the recent atmospheric aerosol literature and reduces bias for high and low light extinction extremes. The revised algorithm differs from the original algorithm in having a term for estimating sea salt light scattering from Cl - ion data, using 1.8 instead of 1.4 for the mean ratio of organic mass to measured organic carbon, using site-specific Rayleigh scattering based on site elevation and mean temperature, employing a split component extinction efficiency associated with large and small size mode sulfate, nitrate and organic mass species, and adding a term for nitrogen dioxide (NO2) absorption for sites with NO2 concentration information. Light scattering estimates using the original and the revised algorithms are compared with nephelometer measurements at 21 IMPROVE monitoring sites. The revised algorithm reduces the underprediction of high haze periods and the overprediction of low haze periods compared with the performance of the original algorithm. This is most apparent at the hazier monitoring sites in the eastern United States. For each site, the PM10 composition for days selected as the best 20% and the worst 20% haze condition days are nearly identical regardless of whether the basis of selection was light scattering from the original or revised algorithms, or from nephelometer-measured light scattering.

Radiance simulations of selected atmospheric species at different observer attitudes for ground-based FTIR spectroscopy: implications for aerosol polluted sites in West Africa

The pure air and clear sky conditions necessary for continuous Fourier Transform Infra-Red (FTIR) measurements of trace gases are issues of concern for West African sites. This is due to possible severe interruption by Sahara dust outbreak, which leaves trails throughout the year. Using data simulated by means of an atmospheric radiative transfer code, it is strengthened that the lower strengths observed for selected trace gas absorption spectra for higher observation altitudes may imply that increasing measurement altitudes or initiating balloon measurements to avoid aerosols and its associated haze conditions would be at the risk of managing reduced FTIR signatures. Continuous FTIR measurements in aerosol-polluted regions on the other hand can be a novel method for establishing more links between mineral aerosols and trace gas mixing ratios and or heterogeneous chemistry. Keywords: Trace gases, FTIR, spectroscopy, aerosols, and atmospheric pollution. Nigerian Journal of Physics Vol. 18 (2) 2006: pp. 227-234

Airborne dust accumulation and soil development in the North-East sector of Gran Canaria (Canary Islands, Spain)

The island of Gran Canaria is located in the eastern Atlantic, to the west of the Saharan Desert, and, as a result of its proximity, is regularly affected by Saharan dust. When this weather condition occurs (haze conditions) the particulate/aerosol accumulation rate was lightly higher than under non-haze conditions (5.4±3.8 mg m −2 h −1 versus 4.3±2.1 mg m −2 h −1). To quantify the contribution of airborne Saharan dust to soil development in northeastern Gran Canaria, aeolian dust was collected weekly at different altitudes and distances from the coast during a year in a series of collection plots. Mean values of dust accumulation rates decreased with increasing altitude (from 79 to 17 g m −2 yr −1). The mineralogy of airborne dust, identified by XRD, was quartz, Mg-calcite, calcite, feldspars, dolomite, magnetite, aragonite, halite, and minor amounts of illite, kaolinite-chlorite and palygorskite. Quartz is considered allochthonous because it is not present in the volcanic substrate of the island. However, the difference in quartz concentration from haze to non-haze conditions was only 10% higher. This suggests an external source, but does not preclude a recycled origin. The recognition of well shaped dolomites, observed by SEM-EDX in collected dust samples and in soils samples of the lowest altitude plot, indicate an edaphic origin, but are later recycled as an airborne component.

Methods and Results from a New Survey of Values for Eastern Regional Haze Improvements

A contingent valuation survey was designed and implemented in 2003 to elicit the willingness to pay for haze reduction in scenic areas of the Eastern United States. This survey updated and enhanced a portion of a 1988 survey, Chestnut and Rowe’s Preservation Values Study, which is commonly used to estimate benefits of haze reduction policies. The 2003 survey incorporated features to address criticisms of the 1988 survey regarding its lack of budget constraints and its simplistic descriptions of changes in visibility. In preparing the new survey, we identified a fundamental error in the 1988 survey regarding the amount of visibility change that respondents were asked to value. When corrected, it reduces the estimates in that study of willingness to pay per unit of visibility change by ~40%. More importantly, we estimate that haze reduction benefits based on that study are overstated by ~70%. Results from our 2003 survey demonstrate that the distribution of willingness to pay is highly skewed, which implies that a haze reduction policy of which the costs per person are equal to the average willingness to pay would be rejected by between 70% and 80% of the public if subjected to a majority vote. Moreover, estimates of willingness to pay are sensitive to how respondents are reminded of their budget constraints. We find a statistically significant decline in willingness to pay when budgetary reminders are included. Finally, we find evidence that a large portion of the willingness to pay appears to be associated with improvement on the worst condition days. Little additional value appears to be associated with improvements to the majority of days that have haze conditions nearer the average. These survey results have important implications for policy making on haze reduction.

Seasonal variability of the aerosol parameters over Kanpur, an urban site in Indo-Gangetic basin

With the growing antropogenic activities and urbanization, pollution level is found to be increasing in the Indo-Gangetic (IG) basin. This trend of increasing pollution has direct impact on the climatic conditions, especially the increase of haze, fog and cloudy conditions in the region. A ground-based CIMEL radiometer has been deployed on the campus of the Indian Institute of Technology (IIT) Kanpur, India, as a part of the Aerosol Robotic Network (AERONET) program with an objective to characterize the aerosols in the IG basin. The optical properties of the aerosols over Kanpur, which is one of the largest industrial cities in the IG basin, show strong seasonal and inter-annual variations. The fine mode urban/industrial aerosols contribute more than 75% to the observed aerosol optical depth (AOD) during the post-monsoon and winter seasons, whereas the natural dusts contribute ∼60% to the AOD during the pre-monsoon and monsoon seasons. Effective radius ( R eff) and volume weighted mean radius ( R V), the two best representative parameter of the coarse and fine modes of aerosol size distribution show maximum values during winter season. The increase in the R V is attributed to the hygroscopic growth of fine mode particles in presence of high relative humidity and favorable temperature condition; but the increase in r eff is due to the association of the fine mode absorbing particles to the coarser dusts. This is also reflected in low values (<0.8) of single scattering albedo (SSA) at coarse mode during the season. Higher values of SSA at fine mode indicate dominance of water-soluble aerosols scattering in nature. The linear regression equations between AOD (at 0.67 μm wavelength) and extinction coefficient due to fine and coarse modes also reveal the relative contribution of the fine and coarse mode particles to the observed optical properties during different seasons in Kanpur.

Air mass modification over Europe: EARLINET aerosol observations from Wales to Belarus

For the first time, the vertically resolved aerosol optical properties of western and central/eastern European haze are investigated as a function of air mass transport. Special emphasis is put on clean maritime air masses that cross the European continent from the west and become increasingly polluted on their way into the continent. The study is based on observations at seven lidar stations (Aberystwyth, Paris, Hamburg, Munich, Leipzig, Belsk, and Minsk) of the European Aerosol Research Lidar Network (EARLINET) and on backward trajectory analysis. For the first time, a lidar network monitored continent‐scale haze air masses for several years (since 2000). Height profiles of the particle backscatter coefficient and the particle optical depth of the planetary boundary layer (PBL) at 355‐nm wavelength are analyzed for the period from May 2000 to November 2002. From the observations at Aberystwyth, Wales, the aerosol reference profile for air entering Europe from pristine environments was determined. A mean 355‐nm optical depth of 0.05 and a mean PBL height of 1.5 km was found for clean maritime summer conditions. The particle optical depth and PBL height increased with increasing distance from the North Atlantic. Mean summer PBL heights were 1.9–2.8 km at the continental sites of Leipzig, Belsk, and Minsk. Winter mean PBL heights were mostly between 0.7 and 1.3 km over the seven EARLINET sites. Summer mean 355‐nm optical depths increased from 0.17 (Hamburg, northwesterly airflow from the North Sea) and 0.21 (Paris, westerly flow from the Atlantic) over 0.33 (Hamburg, westerly flow) and 0.35 (Leipzig, westerly flow) to 0.59 (Belsk, westerly flow), and decreased again to 0.37 (westerly flow) at Minsk. Winter mean optical depths were, on average, 10–30% lower than the respective summer values. PBL‐mean extinction coefficients were of the order of 200 Mm−1 at 355 nm at Hamburg and Leipzig, Germany, and close to 600 Mm−1 at Belsk, Poland, in winter for westerly flows. Whereas the optical depth for westerly flows was typically &lt;0.35 during the summer halfyear, it increased to values of 0.5–0.7 over most of the central European sites during easterly flows. Compared to aerosol sources in Poland and southeastern Europe, the highly industrialized and populated western European region was found to contribute only moderately to the European aerosol burden. Comparably clean conditions (low particle optical depth) prevailed at the Munich site, indicating a sensitive influence of the orography on haze conditions. Estimates of the mean effective (upward minus downward) aerosol mass flux into the atmosphere along the way from the Atlantic Ocean to central Europe (Leipzig), and from Leipzig to Belsk, that are consistent with the optical depth increase, yield values of 0.11–0.17 μg/(m2s) and 0.25 μg/(m2s), respectively. These values correspond to mean effective aerosol mass fluxes for 50 km × 50 km grid cells of the order of 10000 Mg/year and 20000 Mg/year, respectively. The estimates are in reasonable agreement with EMEP emission data.

Influence of ammonia on sulfate formation under haze conditions

In the presence of hygroscopic material, stable aqueous droplets form at relative humidity below 100%. In this work, we examined the role and importance of NH3 in SO2 oxidation under haze conditions. Synthetic deposits composed mainly of NaCl and NaNO3 were exposed to SO2/NH3/air gas mixture under controlled conditions, typical for heavily polluted atmosphere. In contrast to catalytic reaction by Mn(II) in the absence of NH3, which is self-limited, the production of sulfate in the presence of NH3 at RH 80% increases considerably and linearly with time. The catalytic effect of Mn(II) was observed only for NaNO3 deposits. Non-catalytic SO2 oxidation in the presence of NH3 is negligible below the deliquescent relative humidity, i.e. RH<75%. Above this value a considerable increase of sulfate formation in a narrow range of relative humidity (75–80%) was noticed. We found out that the reaction rate is not proportional to the volume of condensed water; we suggest that available surface play a role in limiting the reaction. The rate of conversion for both pure salts at RH⩾80% was found to be 1.1% h−1 ([SO2]=2 ppm, [NH3]=1 ppm, T=10°C), which is more than an order of magnitude higher in comparison with our previous results on MnCl2/NaCl and MnCl2/NaNO3 at RH=80% in the absence of NH3.

Analyses of Aerosol Events Observed at Four Sun Photometer Sites in Japan during March-April 2002

Aerosol-induced atmospheric optical phenomena were analyzed at four sun photometer sites in Japan, viz., Ryori (39°02´N, 141°50´E), Tsukuba (36°03´N, 140°08´E), Yonagunijima (24°28´N, 123deg;01´E), and Minamitorishima (24°18´N, 153°58´E), over the period MarchHApril 2002 to elucidate the causes of such phenomena, and explain regional differences. Using observed optical properties, the phenomena were classified into three kinds of aerosol events: Type A, Type B, and Type C, which, respectively, correspond to relatively clear conditions, typical Kosa conditions, and haze conditions. The frequency of occurrence of these aerosol events was found to be significantly different at the four observation sites in Japan during the observation period. Type B events were found to occur rather frequently in Ryori in northern Japan. The severe Kosa events observed at Ryori on April 10, 2002, which constitute a case study, passed over Northeast China where dust storms have rarely been reported before 2000. The smallest mean aerosol optical depth at 500 nm (τ500) and Angstrom exponent (α) were observed in Minamitorishima. However, according to other studies, the mean τ500 in Minamitorishima was larger than those in the eastern Pacific, which showed that the influence of the Asian outflow on atmospheric optical properties was still significant even 3,000 km away from the Asian continent. The mean τ500 and α, as well as the frequency of occurrence of Type C events, were the largest at our observation site in Yonagunijima. Based on the trajectory analysis obtained during the observation period, the high frequency of Type C events at Yonagunijima was ascribed to the haze from biomass burning in Southeast Asia and/or urban pollution in coastal areas in Southeast China. The frequency of Type C events in Ryori and Tsukuba indicated that haze is not an uncommon occurrence, not only in southern Japan, but also in central and northern Japan, and that, along with Kosa events, they may affect atmospheric optical properties over Japan in the spring.

Sulfate formation on synthetic deposits under haze conditions

Particles and droplets containing liquid water represent very important media for chemical reactions. The presented investigation was focused on the formation of acidic product (sulfate) during SO 2 oxidation in the presence of manganese under haze conditions, i.e. at relative humidity below 100%. Since the reaction kinetics of the transformation of atmospheric trace gases depend on the concentration and composition of the aqueous phase, the influence of these parameters was studied. Synthetic deposits of varying composition containing mainly NaCl and NaNO 3 were exposed to SO 2 /air gas mixture at concentrations typical for heavily polluted atmosphere. Experiments were carried out in a specially designed reaction chamber under controlled conditions. Formation of sulfate was negligible below the deliquescent point on both matrices in the presence and absence of Mn(II). However, above this threshold relative humidity, the production of SO 4 2− was observed only in the presence of Mn(II). The reaction rate increases exponentially with relative humidity. A considerable increase was noticed at relative humidity above 85%, where the amount of condensed water becomes substantial. For example, the reaction rate at SO 2 concentration of 3 ppmv on MnCl 2 /NaCl deposits at T =10°C increased from 3.2 to 16.6 mg SO 4 2− /(g salt h), if the RH is increased from 80% to 90%. Our results also showed that the process of SO 2 conversion on deposits is self-limited due to a decrease of pH of condensed water.

Mixing states of individual aerosol particles in spring Arctic troposphere during ASTAR 2000 campaign

The present study mainly focuses on the mixing states of aerosol constituents and their vertical distribution in spring Arctic troposphere during the ASTAR 2000 campaign (T. Yamanouchi et al., Arctic Study of Tropospheric Aerosol and Radiation (ASTAR) campaign: An overview and first results, submitted to Bulletin of the American Meteorological Society, 2002) (hereinafter referred to as Yamanouchi et al., submitted manuscript, 2002). Sulfate and soot were identified as major aerosol under both Arctic haze and background conditions, and sea‐salts are major only in lower troposphere (&lt;3 km above sea level). Mineral/dusts and unknown species were obtained as minor constituents during the ASTAR 2000 campaign. Airborne aerosol measurements were carried out under the Arctic haze (23 March), and aerosol‐enriched (20 March and 12 April) conditions. The highest relative abundance of soot (∼94.7%) was observed in free troposphere on 23 March, when the heaviest Arctic haze condition during the ASTAR 2000 campaign (Yamanouchi et al., submitted manuscript, 2002) was transported directly from Russian industrial regions to the measuring area for several days. Moreover, whereas the external mixing of soot and sulfate dominated under the Arctic haze and aerosol enriched conditions, in the background conditions the internal mixing is dominant. On the other hand, most of aerosol particles containing sulfate had the external mixing states with soot and other aerosol constituents in the free troposphere under both the Arctic haze and background conditions. Sea‐salts are dominant only in the lower troposphere (&lt;3 km asl), although a few sea‐salt particles were observed in the middle‐upper troposphere (3–7 km). Some sea‐salt particles were modified (Cl− depleted) in the lower troposphere (&lt;3 km) during the ASTAR 2000 campaign.

Vertical variations of sea-salt modification in the boundary layer of spring Arctic during the ASTAR 2000 campaign

Airborne and ground-based aerosol/gas measurements were carried out in Svalbard between mid-March and mid-April 2000. From the viewpoint of vertical features of sea-salt modification in the lower troposphere (1500 m) of the Arctic spring, more than 1000 individual sea-salt particles were analyzed with scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDX) in the present study. Individual particle analysis suggested a vertical gradient of sea-salt modification in fine sea-salt particles with an altitude of 59–1485 m above sea level (asl), e.g. chlorine liberation rates of 33.0% (212 m asl) and 81.0% (1266 m asl) on 15 March, and 72.7% (100 m asl), 83.8% (495 m asl) and 95.8% (1411 m asl) on 26 March. Sea salts may be dominantly modified with SO2 and SO42− under Arctic haze conditions with higher SO2 concentration (≥2 nmol m−3), whereas they are dominantly modified with NO3− and reactive nitrogen oxides under Arctic background conditions, with [HNO3] of 0.15–1.3 nmol m−3 and [SO2] of 0.04–2 nmol m−3. Vertical trends in sea-salt modification suggested that it makes a significant contribution to the formation of reactive halogen species in the upper boundary layer and the lower free troposphere of the spring Arctic.

Improving image quality in poor visibility conditions using a physical model for contrast degradation

In daylight viewing conditions, image contrast is often significantly degraded by atmospheric aerosols such as haze and fog. This paper introduces a method for reducing this degradation in situations in which the scene geometry is known. Contrast is lost because light is scattered toward the sensor by the aerosol particles and because the light reflected by the terrain is attenuated by the aerosol. This degradation is approximately characterized by a simple, physically based model with three parameters. The method involves two steps: first, an inverse problem is solved in order to recover the three model parameters; then, for each pixel, the relative contributions of scattered and reflected flux are estimated. The estimated scatter contribution is simply subtracted from the pixel value and the remainder is scaled to compensate for aerosol attenuation. This paper describes the image processing algorithm and presents an analysis of the signal-to-noise ratio (SNR) in the resulting enhanced image. This analysis shows that the SNR decreases exponentially with range. A temporal filter structure is proposed to solve this problem. Results are presented for two image sequences taken from an airborne camera in hazy conditions and one sequence in clear conditions. A satisfactory agreement between the model and the experimental data is shown for the haze conditions. A significant improvement in image quality is demonstrated when using the contrast enhancement algorithm in conjuction with a temporal filter.

Height dependent absorption of solar radiation in the arctic atmosphere

Measured profiles of the total flux of solar radiation are carried out under conditions of the arctic haze during spring in the Arctic. Vertical profiles of the arctic atmosphere heating rate obtained show the complex, multilayer structures of the arctic haze aerosol. These investigations yielded no considerable differences in the haze structure both in the Canadian and in the Russian sectors of the Arctic. Atmosphere heating rate due to the absorption of solar fluxes was found up to 1.8 K/day. The minimum of the aerosol density was found to be northward of Greenland. The heating rates in this region were comparable with the values peculiar to the standard atmosphere. The investigations of the horizontal distribution of the broadband solar radiation fluxes have shown that the aerosol structure of arctic haze is highly inhomogeneous over all regions of observations. The changes of aerosol vertical distributions were notable over the distance 200 km. It was also found, that the aerosol layers located in the altitudes region of 4000–7000 m were playing the predominant role in the absorption of solar radiation.

Effect of physical properties of atmospheric aerosols on path radiance

Using a set of simplified radiative transfer equations, the effects of the changes in the physical properties (such as columnar size distribution, optical depth and refractive index) of atmospheric aerosols on the upwelling atmospheric path radiance are investigated for a nadir viewing remote sensor at various solar illumination angles in the context of developing operational methods for correcting radiances received by remote sensing satellites for atmospheric effects. It is seen that at low solar illumination angles and high haze conditions (aerosol optical depths > 0.5) the path radiance depends strongly on the nature of the aerosol size distribution, whereas for low to moderate values of aerosol optical depths ( < 0.5), the path radiance increases nearly linearly with optical depths. Spectral variations indicate a large increase in path radiance with decrease in wavelength.