Effects of urbanization and forest type on species composition and diversity,forest characteristics,biomass carbon sink,and their associations in Changchun,Northeast China:implications for urban carbon stock improvement

Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban forests and improvement of function.To clarify the effect of two forest types with different urbanization intensities,we determined differences in vegetation composition and diversity,structural traits,and carbon stocks of 152 plots(20 m×20 m)in urban park forests in Changchun,which had the largest green quantity and carbon density effectiveness.We found that 1.1-fold thicker and healthier trees,and 1.6-to 2.0-fold higher,healthier,denser,and more various shrubs but with sparser trees and herbs occurred in the central urban forests(p<0.05)than in the outer forests.The conifer forests exhibited 30–70%obviously higher tree aboveground carbon sequestration(including stem and leaf)and 20%bigger trees,especially in the outer forests(p<0.05).In contrast,1.1-to 1.5-fold higher branch stocks,healthier and more diverse trees were found in broadleaved forests of both the inner and outer forests(p<0.05).Plant size and dominant species had similarly important roles in carbon stock improvement,especially big-sized woody plants and Pinus tabuliformis.In addition,a higher number of deciduous or needle species positively affected the broadleaved forest of the central urban area and conifer forest of the outer urban area,respectively.These findings can be used to guide precise management and accelerate the improvement of urban carbon function in Northeast China in the future.

Geospatial Analysis of Urban Heat Island Effects and Tree Equity

In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest access. Urban Heat Island Effects are measurable phenomenon that are being experienced by the world’s most urbanized areas, including increased summer high temperatures and lower evapotranspiration from having impervious surfaces instead of vegetation and trees. Tree canopy cover is our natural mitigation tool that absorbs sunlight for photosynthesis, protects humans from incoming radiation, and releases cooling moisture into the air. Unfortunately, urban areas typically have low levels of vegetation. Vulnerable urban communities are lower-income areas of inner cities with less access to heat protection like air conditioners. This study uses mean evapotranspiration levels to assess the variability of urban heat island effects across the state of Tennessee. Results show that increased developed land surface cover in Tennessee creates measurable changes in atmospheric evapotranspiration. As a result, the mean evapotranspiration levels in areas with less tree vegetation are significantly lower than the surrounding forested areas. Central areas of urban cities in Tennessee had lower mean evapotranspiration recordings than surrounding areas with less development. This work demonstrates the need for increased tree canopy coverage.

Study on the Urbanization of Nanjing City and Its Greenhouse Effect

To study the relationship between the enlargement of Nanjing City and urban greenhouse effect,the temperature of Nanjing Station and its suburban stations during 1961-2000 was analyzed.The results showed that the temperature of Nanjing area has increased gradually and the urban heat island effect has developed quickly.The average temperature increment in winter is the greatest,followed by that in spring,autumn and summer,most of which was caused by the greenhouse effect in Nanjing area.Finally several effective countermeasures have been proposed correspondingly.

Analysis on the Variation Characteristics of Temperature in Anqing City and Urban Heat Island Effect

[Objective] The aim was to analyse the variation characteristics of temperature in Anqing City and urban heat island effect.[Method] Based on the observation data of temperature from Anqing Station,other surrounding meteorological stations and local automatic meteorological stations in suburbs,the annual variation of temperature and regional consistency was analysed,then the abrupt change of annual average temperature was tested by Mann-Kendall test,finally the influences of urban heat island effect on temperature variation in Anqing Station were studied.[Result] Affected by station migration and urban construction,the annual average temperature increased significantly in Anqing Station from 1977 to 2009,and the rising was more prominent after the middle of the 1990s.Mann-Kendall test showed that the change of temperature in Anqing Station was obviously abrupt around 1993;because of the development of urbanization,average temperature in Anqing Station was 0.8 ℃ higher than that in suburbs,and the minimum temperature rose more remarkably.In addition,urban heat island effect was the strongest in spring,followed by summer and autumn,while it was the weakest in winter.[Conclusion] The effects of urbanization development on the temperature in Anqing City were understood through this research.

Diurnal Variations of Summer Precipitation in the Beijing Area and the Possible Effect of Topography and Urbanization

The present study examined the diurnal variations of summer precipitation in the Beijing area by usingsubdaily precipitation and wind observations. A combined effect of topography and urbanization on thecharacteristics of diurnal variations was suggested. It was shown that stations located in the plain areaexhibited typical night rain peaks, whereas those in the mountainous area exhibited clear afternoon peaks ofprecipitation diurnal variations. The precipitation peaks were associated with wind fields around the Beijingarea, which were found to be highly modulated by mountain-valley circulation and urban-country circulation.The lower-tropospheric wind exhibited a clear diurnal shift in its direction from north at 0800 LST to southat 2000 LST, which reflected mountain-valley circulation. The transitions from valley to mountain windand the opposite generally happened after sunset and sunrise, respectively, and both occurred earlier for thestations located closer to mountains. By comparing the diurnal variations of precipitation at stations in anortheast suburb, an urban area, and a southwest suburb, it was revealed that the northeast suburb grouphad the highest normalized rainfall frequency, but the southwest group had the lowest from late afternoon tolate evening. On the contrary, in the early morning from about 0200 to 1000 LST, the southwest group andurban group had the highest normalized rainfall frequency. This pattern might originate from the combinedeffects of mountain-valley topography and urbanization.

Review of recent studies of the climatic effects of urbanization in China

This paper summarizes recent studies on the effects of urbanization on climate in China. The effects of urbanization on local climate trends have been re-estimated based on homogenized observations and using improved methods. In this respect, the effect of urbanization on the observed warming trend of local surface air temperatures during the last few decades is determined as being about 20% at urban stations such as the Beijing Observatory. The large-scale weakening trend of wind speed is also about 20% more prominent at the city center than its surroundings. The effect of urbanization on precipitation is not profound, but results of high-resolution regional climate modeling suggest that this effect may depend on the urban extent. Although the urban heat island(UHI) should favor local atmospheric convection and hence precipitation, the increasingly extending urban land-use may reduce precipitation over the urban cluster in North China. It is found that urbanization can play a more notable role in extreme events than usual weather. High-resolution simulations show a positive feedback between the UHI and the super-heat wave in Shanghai during Julye August 2013. Relevant studies dealing with urban climate adaptation are discussed in relation to recent ?ndings.

Characteristics of urban heat island effect in Lhasa City

This paper analyzes the Urban Heat Island （UHI） effect in Lhasa City of Tibet using meteorological observations, the Normalized Difference Vegetation Index （NDVI）, Land Surface Temperature （LST） data obtained from Earth Observing System/Moderate resolution Imaging Spectroradiometer （EOS/MODIS） information, and correlation and composite analyses. The results show： （1） Areas with high temperature are primarily located in the center of the city or nearby counties, while low temperature areas are in the suburbs of counties. The area with high temperature has expanded in recent years and some high-temperature centers have even migrated to certain other regions. （2） The UHI intensity tends to be stronger both in annual and seasonal variations, especially in winter. Also, LST is somewhat positively related to mean air temperature. （3） A negative correlation exists between the changes of LST and NDVI with the increase of vegetation from urban to rural areas in different seasons. （4） The UHI intensity is negatively correlated with precipitation while positively correlated with wind speed, and the relation between the UHI intensity and evaporation varies with the seasons, namely, the intensity is positively correlated with summer evaporation but negatively corre- lated with winter evaporation. （5） UHI intensity might be enhanced by intensified urbanization, wherein built-up areas expand, there is increased heat from human activity, and there is more artificial heat input to the atmosphere.

AGGLOMERATION AND RADIATION EFFECT OF THE PULL OF URBANIZATION

In order to explore the train of thought for China’s urbanizing development and coordinated rural economic development, and to find good ways of solving rural problems through urbanization, this paper absorbs the push-and-pull forces theory and the systematic dynamic theory in the traditional population migration theories, views urbanization as a dynamic system, makes research on the push-and-pull mechanism of urbanization. The pulling power of urbanization is analyzed according to two aspects, the agglomeration effect and the radiation effect of cities. The agglomeration effect provides continuous propelling force for urbanization, and the radiation effect further accelerates the urbanization process by pushing forward the development of rural economy. Of course, the slow development of urbanization can result in the hindrance to rural economic development.

Urbanization effect on precipitation over the Pearl River Delta based on CMORPH data

Based on the satellite data from the Climate Prediction Center morphing(CMORPH) at very high spatial and temporal resolution, the effects of urbanization on precipitation were assessed over the Pearl River Delta(PRD) metropolitan regions of China. CMORPH data well estimates the precipitation features over the PRD. Compared to the surrounding rural areas, the PRD urban areas experience fewer and shorter precipitation events with a lower precipitation frequency(ratio of rainy hours, about 3 days per year less); however, short-duration heavy rain events play a more significant role over the PRD urban areas. Afternoon precipitation is much more pronounced over the PRD urban areas than the surrounding rural areas, which is probably because of the increase in short-duration heavy rain over urban areas.

Spatial Effect of Mineral Resources Exploitation on Urbanization:A Case Study of Tarim River Basin,Xinjiang,China

Mineral resources exploitation significantly affects the spatial structure and evolutive trend of urbanization in arid areas.In this study,the spatial autocorrelation method and the spatial computation model were used to investigate the spatial impacts of mineral resources excavation and processing on comprehensive level of urbanization in the Tarim River Basin,Xinjiang,China for the years of 2000,2006 and 2008.The results are as follows:1)There was a spatial correlation of the development of mineral resources industry and the comprehensive level of urbanization in 2006 and 2008,with the spatial concentration trend rising significantly in 2006 and decreasing in 2008.2)The patterns of local spatial concentration of mineral resources industry and of the comprehensive level of urbanization were relatively stable,and the two patterns showed signs of spatial correlationship.The higher was the degree of the concentration of mineral resources industry,the stronger was its impact on the spatial clustering of urbanization.3)In 2000, mineral resources excavation and processing had a significant positive impact on the comprehensive level of urbanization in the region but not in its adjacent regions.However,in 2008,mineral resources excavation and processing significantly raised the comprehensive level of urbanization not only in the region but also in its neighboring regions.This research demonstrates that the development of mineral resources industry can strongly affect the trends and spatial patterns of urbanization.

Evolutionary Pattern and Effect of Administrative Division Adjustment During Urbanization of China:Empirical Analysis on Multiple Scales

The adjustment of administrative divisions is one of the important factors guiding China's urbanization, which has profound economic and social effects for regional development. In this paper, we comprehensively describe the process of the adjustment of administrative divisions at provincial and municipal levels in China and summarize the effects on the basic structure and patterns of the spatial development. We quantitatively assess the effects on fields such as urbanization and social economy through the use of multidimensional scaling. The results show that: 1) Upgrading county to municipality(or city-governed district) is the main way of adjusting the administrative divisions. It is also an important factor in the spatial differentiation of interprovincial urbanization. China's population urbanization can be divided into four patterns including interprovincial migration, provincial migration, natural growth, and growth caused by the adjustment of administrative divisions, which is also the main reason for the increased Chinese urbanization rate at the provincial level. 2) Taking the city of Beijing as an example, we generalize five adjustment patterns made to administrative divisions: the set-up of sub-districts, the set-up of regional offices, the upgrading of townships to sub-districts, the upgrading of townships to towns, and the set-up of towns and the addition of new regional offices. We summarize the municipal urban spatial structure, including the sub-district office area in the central urban area, the regional office area in the new urban area, the mixed area of villages, towns, and sub-district offices in the suburb area, and the township area in the outer suburb area. 3) The adjustment of administrative divisions triggers a significant circulative accumulation effect, resulting in the spatial locking of population and industrial agglomeration. It affects the evolution of the urban spatial form and plays an important role in shaping the urban spatial structure to move to the characteristic of multicenter. In general, the adjustment of administrative divisions was an important factor affecting the inflated statistical level of urbanization and also an important driving force for the evolution of Chinese urban spatial organization structure.

A Numerical Study of the Urban Intensity Effect on Fog Evolution in the Beijing-Tianjin-Hebei Region

The influence of urban intensity on fog evolution in the Beijing-Tianjin-Hebei (BTH) region (China) is investigated numerically with the the Weather Research and Forecasting (WRF) model coupled with the urban canopy parameterization-building energy model (UCP- BEM) urban physics scheme. The experiments were designed with a focus on the influence of different urban intensities, which are represented by a different fractional coverage of natural land, buildings, and energy consumption inside buildings in an urban environment. The results of this study indicate that urban areas notably influence fog evolution when natural land is reduced to a small fraction (e.g., less than 10%). Developed land changes fog evolution through urban effects. Higher urban intensity (HUI) generally results in warmer temperatures and lower wind speeds throughout the day, while inhibiting morning specific humidity loss and afternoon specific humidity gain because of the HUI effect on surface heat flux, surface roughness, and surface moisture flux. HUI leads to later and weaker liquid water content formation, with a higher liquid water content base, primarily due to its effect on near surface temperatures. This finding implies that HUI may inhibit the conditions for fog formation. In addition, urban areas with equal natural and developed land coverage seem to greatly enhance the upward surface moisture flux, which is attributed to the combination of a relatively large potential evaporation on developed land and an ample moisture supply from natural land. As a result, the specific humidity increases in the afternoon.

Spatial and temporal analysis of urban heat island effect over Tiruchirappalli city using geospatial techniques

Alterations made to the natural ground surface and the anthropogenic activity elevate the surface and air temperature in the urban areas compared with the surrounding rural areas,known as urban heat island effect.Thermal remote sensors measure the radiation emitted by ground objects,which can be used to estimate the land surface temperature and are beneficial for studying urban heat island effects.The present study investigates the spatial and temporal variations in the effects of urban heat island over Tiruchirappalli city in India during the summer and winter seasons.The study also identifies hot spots and cold spots within the study area.In this study,a significant land surface temperature difference was observed between the urban and rural areas,predominantly at night,indicating the presence of urban heat island at night.These diurnal land surface temperature fluctuations are also detected seasonally,with a relatively higher temperature intensity during the summer.The trend line analysis shows that the mean land surface temperature of the study area is increasing at a rate of 0.166 K/decade with p less than 0.01.By using the spatial autocorrelation method with the urban heat island index as the key parameter,hot spots with a 99 percent confidence level and a 95 percent confidence level were found within the urban area.A hot spot with 95 and 90 percent confidence level was identified outside the urban area.This spike in temperature for a particular region in the rural area is due to industry and the associated built-up area.The study also identified cold spots with a 90 percent confidence level within the rural area.However,cold spots with a 95 and 99 percent confidence level were not identified within the study area.

The Effects of Road and Other Pavement Materials on Urban Heat Island (A Case Study of Port Harcourt City)

Urban centers are consistently exhibiting higher temperature than its surrounding suburban rural areas. The large amount of heat generated from urban structures such as road materials and pavement materials and other anthropogenic heat sources are the main causes of Urban Heat Island (UHI). The sources of data for this research included primary and secondary sources. Other techniques employed for data collection were direct measurement and readings on the road and pavement materials. The research found out that, there was consistency in rising temperature at different time of the day by the different road and pavement materials. Asphalt has the greatest effect of increasing the urban temperature four degrees higher, followed by concrete, three degree rise in temperature, and earth (ordinary ground) by two degree rise and vegetation (grass) by one degree rise in temperature. The overall effect on the residents of the study area ranges from increase in hotness of the day;44.6% respondents agrees;while 34.3% says it affects the ambient air quality of the area, and other effects such as increased ground level ozone, suffocation, sleeplessness and restlessness as a result of excessive high temperature especially at night are identified in this paper. The research recommends the review or redesigning of the entire Port Harcourt city Master Plan to make provision for creation of more green areas rather than pavements and concreted areas to reduce the effects of (UHI) and ultimately improve the comfort and living conditions of the people in a the garden city Port Harcourt.

Change in Urban Wetlands and Their Cold Island Effects in Response to Rapid Urbanization

The cold-island effect of urban wetlands has received increasing attention in recent years due to its important role in the alleviation of urban heat islands.Hangzhou,a representative rapidly urbanizing city with rich wetlands in China,was selected as a case study for researching the changes that the urban wetlands have undergone and their impact on the urban thermal environment.Land surface temperature(LST) was acquired from the thermal infrared data of Landsat 5 Thematic Mapper(TM) images in 1990,1995,2000,2006,and 2010,using the single-channel method.The results are as follows:1) considering the changes in land use,the urban wetlands located to the west of Hangzhou have decreased significantly during 1990–2010 because of rapid urbanization.In the Xixi Wetland,the change in land use was relatively small and most of the water body and vegetation were preserved.However,to the east of the Xixi Wetland,large areas of water body and vegetation have been replaced by built-up land as a result of the urbanization process;2) considering the change in LST,it was found from land surface temperature retrieval that the changing spatial pattern of the thermal field was highly correlated with land use changes.Low temperature regions of the eastern Xixi Wetland were gradually eroded by high temperature regions,and the centroid of the heat island in East Xixi was found to be constantly shifting westward.In addition,the difference in LST between the Xixi Wetland and East Xixi has increased;3) considering the impact factors for this area,land use structure and patch shape were found to have a significant impact on LST,shown by the results of multiple linear stepwise regressions.Increasing the size of the wetlands in urban planning is considered to be the most effective measure in alleviating the urban heat island effect.Moreover,reducing the spatial complexity of landscape patches also contributes to the alleviation of the urban heat island effect.

Analysis of Urban Land Use and Its Effects on Air Environment in Chengdu, Western China from 1992 to 2008

Large-scale development of urban land use has led to change of a variety of natural processes and ecological processes, resulting in complex eco-environmental consequences. The objective of this study was to analyze the urban land use and its impact on air environment effect in Chengdu, western China from 1992 to 2008 following the RS (Remote Sensing) and GIS technique. The environmental effects data of urban land use was extracted and analyzed by overlaying layers of urban land use and the density of nitrogen dioxide and total suspended particulate matter in sampling points data concerning to the air quality of the environment in Chengdu based on GIS spatial analysis method. The results show that the main feature of urban land use change was substantial reduction of cultivated land and construction land and forest land increased significantly within the study area from1992 to 2008. The temporal-spatial change was notable in study period time. Land use has a significant impact on urban air environment, the chroma change of nitrogen dioxide derived from forest land was obvious, the area occupied by different nitrogen dioxide chroma was the largest. The urban land use impact on the highest class chroma of total suspended particulate matter was notable and its area was the greatest. The results show also the spatial distribution of nitrogen dioxide chroma and total suspended particulate matter chroma in study area is reduced following from Qingbaijiang District-Xindu District-downtown to both sides. The spatial distribution of industry, mining and traffic land is basically the same chroma spatial distribution. Therefore, the results of this study provide a scientific basis for improvement air environment quality, the urban sustainable development and a scientific response for decisions from the municipal governments.

Changes of Urban Boundary Layer Thermodynamic Stability Induced by Heat Island Effect and Their Influences on Precipitation

[Objective] The aim was to study the characteristics of the changes of the urban boundary layer thermodynamic stability induced by heat island effect and their influences on precipitation.[Method] Proceeding from the thermodynamic equation,the changes of urban boundary layer thermodynamic stability caused by the urban heat disturbance and the mean state of heat island effect were discussed.The influence of the changes of urban boundary layer thermodynamic stability on the precipitation was expounded.Combining with case study of precipitation in Xi’an,the test was verified.[Result] Under interaction between the disturbed temperature and disturbed airflow,the boundary thermal disturbed stability(θ’z) was positive in the urban zone,as well as in the upstream and downstream areas of the city.But the stability in the urban zone was weaker than the suburbs,which favored for the short-time convective precipitation.For the boundary layer mean thermal stability(θ-0-0z) under the interaction between the mean airflow and mean environmental temperature,if the city zone was in the front of the warm ridge,the stability in the upstream of the city weakened which increased the instability of the boundary layer,while it increased in the downstream of the city.It was contrary if the city zone was in the font of the cold trough.For the mean airflow(prevailing wind) and the mean horizontal disturbed temperature,if it was upward motion in the boundary layer,the boundary layer mean thermal disturbed stability(θ’-0z) was negative in the downstream and positive in the upstream.Strong precipitation occured in the upstream of the city.It was contrary if it was descending air in the boundary layer.[Conclusion] The above results served some references for the fine city forecast.

Analysis of Spatial Scale Effect on Urban Resilience:A Case Study of Shenyang,China

Based on urban physical space and theory of landscape ecology,a triune assessment framework—‘size-densitymorphology’—was constructed in order to analyze the spatial pattern and the scale effect of urban resilience in Shenyang of China in 2015,and to explore the main impact factors of landscape under different spatial scale backgrounds.The results show that:1)Urban resilience is an optimal combination of the resilience of size,density,and morphology.The urban resilience of Shenyang displays scale effect;the overall resilience level increases with the increase in scale,while the spatial difference and spatial similarity tend to decrease resilience.2)As 2 km,1 km and 2 km are scale inflection points of average value curves for size resilience,density resilience and morphology resilience,respectively in an urban setting;the optimal scale unit of comprehensive resilience is 1 km.Choosing 1 km–2 km as the basic spatial scale better depicts overall pattern and detailed characteristics of resilience in Shenyang.The spatial amplitudes of 0.5 km and 1 km are sensitive points for spatial autocorrelation of morphology and density resilience,size,and comprehensive resilience to scale effect.3)The major landscape factors of urban size and morphology resilience transform with scale expansion.Aggregation index(AI)has a significant impact on urban resilience at different scales;its influence increases significantly with the increase in scale.4)The high-level area of comprehensive resilience in Shenyang is the eastern ecological corridor area,while the low value area is the peripheral extension area of the city.To promote the overall level of resilience in Shenyang,this paper argues that the construction of ecological infrastructure should be strengthened in the peripheral extension area in a balanced manner.In the city center,population and building density should be controlled;the intensity of human activities should be reduced;impetus should be placed on landscape heterogeneity;and the homogeneous expansion of the area of construction should be prevented.In the eastern ecological corridors,the exploitation of ecosystem lands should be strictly controlled,and the integrity of the green landscape patches should be maintained.

Urbanization strengthens the edge effects on species diversity and composition of woody plants in remnant forests

Background:Urban remnant forests are embedded in urban areas and are threatened directly and indirectly by urbanization.The direct effects(e.g.,loss of area)have been well studied.However,knowledge about the indirect influence of urbanization through edge effects on the biodiversity in remnant forests is limited.Methods:In this study,we surveyed woody plant species in 72 plots in nine remnant forest patches in Guiyang,China.We examined the influences of urbanization and edge effects on the species diversity and composition of woody plants in remnant forests.We compared alpha diversities and quantified compositional dissimilarities in interior and edge sites at different levels of urbanization.We also measured the niche width of the recorded plant species and assessed whether high levels of urbanization and edge effects increased the number of generalist species.Results and conclusions:The Shannon index,the Simpson index and the Pielou index of adult trees were lowest in the edge habitat under high levels of urbanization.Significant differences in the Shannon index and the Simpson index of sapling/seedling were detected between interior and edge sites under low urbanization.The edge effects on the species composition of adult trees were intensified by high levels of urbanization.Woody plant species with wide niche widths were more abundant at edge sites under high levels of urbanization.Therefore,we recommend that urban expansion surrounding remnant patches should be strictly controlled to alleviate edge effects on biodiversity.

Impact of the Urban Heat Island Effect on Ozone Pollution in Chengdu City,China

With the advancement of urbanization,the urban heat island effect and ozone pollution have become hot issues in urban research.The urban heat island effect can impact ozone conversion,but its mechanism of action is unclear.In this study,the effects of the urban heat island effect on ozone concentration in Chengdu City,China,were investigated by comparing the ozone concentration under different heat island levels with ozone data from March 2020 to February 2021 and the temperature and wind field data of ERA5-Land during the same period.The results showed that:1)regarding the distribution characteristics,the ozone concentration in Chengdu presented a‘high in summer and low in winter’distribution.The ozone concentration in summer(189.54µg/m^(3))was nearly twice that in winter(91.99µg/m^(3)),and the ozone diurnal variation presented a‘single peak and single valley’distribution,with a peak at 16:00.2)For the characteristics of the heat island effect,the heat island intensity in Chengdu was obviously higher in spring than in other seasons,and the diurnal variation showed a‘single peak and single valley’distribution,with the peak and trough values appearing at 9:00 and 17:00,respectively.Spatially,the eastern part of Chengdu was a heat island,while the western and northwestern parts were mostly cold island.3)The correlation analysis between heat island intensity and ozone concentration showed a significant positive correlation but with a 7–8 h time lag.Ambient air temperature was not the main factor affecting ozone concentration.The heat island effect impacts the ozone concentration in two ways:changing the local heat budget to promote ozone generation and forming local urban wind,which promotes ozone diffusion or accumulation and forms different areas of low and high ozone values.