Introduction

Urban air pollution is the most serious environmental problem faced by countries around the world, and has seriously impacted urban public health and sustainable social development (Ghasempour et al. 2021). Rapid urbanization has drastically exacerbated urban environmental problems such as air pollution (Strosnider et al. 2019; Hao et al. 2020). Urban ozone pollution (UOP) has become a serious environmental problem in many cities and poses a serious threat to the health of urban residents (Yazdi et al. 2019). The average surface UOP concentrations in the summer in major Chinese cities increased by approximately 20% in 2016–2017 compared to 2013–2014 (** and assessment of PM10 and O3 removal by woody vegetation at urban and regional level. Remote Sens-Basel 9(8):791" href="/article/10.1007/s10980-024-01838-8#ref-CR11" id="ref-link-section-d180659034e1628">2017; Wei et al. 2022). We used average ozone concentration data for the three years from 2016 to 2018. The National Ambient Air Quality Standards of China (NAAQS) and the WHO introduced concentration limits for the maximum daily 8-h average (MDA8) O3 concentrations (Table 2).

Table 2 The different O3 pollution levels based on the NAAQS standard
Full size table

Driving factors

To investigate the effects of natural and anthropogenic factors on urban atmospheric ozone concentrations, key indicators of these factors were selected in this study. Natural factors included temperature and precipitation, which have accelerated or slowed the effects on ozone concentrations, from the daily meteorological dataset of basic meteorological elements of the Chinese national ground-based meteorological stations (V3.0) (http://www.data.cma.cn/) (Table 3). Anthropogenic factors included urban morphology (Table 1), highway passenger traffic, and population density. Traffic exhaust is an important precursor to ozone production, and highway passenger traffic reflects the amount of urban traffic flow, which is from the Chinese Urban Statistical Yearbook 2018. (Zhang et al. 2021). Our study found that the AH and BHR of 3D building morphology indicators were negatively correlated with ozone concentrations, with taller buildings resulting in lower ozone concentrations, most significantly in autumn and winter. Within a specific height range near the ground, the higher the floor is, the higher the wind speed, accelerates the dispersion and weakens the ozone concentration. The shading effect of the higher floors weakens the solar radiation in the city, therefore weakening the average temperature in parts of the city and slowing ozone production. On the other hand, tall buildings in cities are mainly located in urban centers, and the main sources of ozone production are the industrial areas of cities. In contrast, industrial emissions from cities generally do not spread to urban centers; therefore, ozone concentrations in high-floor locations are low. However, the results of our study differ from those of previous studies; for example, taller floors increase wind-blocking and thus inhibit the dispersion of urban ozone concentrations (Taseiko et al. 2009), and the effect of average building height on air pollutants is quite ambiguous (Yang et al. 2020). Therefore, the analysis of the distribution and dispersion of ozone concentrations must be combined with the height and density of buildings, which requires a comprehensive analysis.

The space congestion degree and ozone concentration show an obvious positive correlation—the more crowded the urban building space, the higher the ozone concentration in the city; on the one hand, buildings can function as wind barriers—the narrower the area, the less wind speed and wind force, and hence the ozone diffusion is weakened (Hoek et al. 2008; Weber et al. 2014; Peng et al. 2018); on the other hand, confined buildings make interactions between single buildings; solar radiation is repeatedly reflected and absorbed, and the accumulation of solar radiation leads to a higher temperature, which accelerates ozone generation (Xu and Chen H 2021).

Our study showed that anthropogenic factors are the dominant factors affecting ozone in urban areas. Studies have shown that the main sources of ozone are small amounts of natural sources and large amounts of anthropogenic sources, including nitrogen oxides and volatile organic compounds (Lu et al. 2019; Wang et al. 2020). Anthropogenic factors provide a large number of precursors for ozone production, while natural factors accelerate or diminish ozone production or dispersion (Wang et al. 2020). Anthropogenic factors are the main source of ozone production and play a major role in influencing ozone concentrations, whereas natural factors play a minor role. Building factors are an important part of anthropogenic factors, urban 2D building morphology influences the industrial layout and transportation planning of the city, increasing or decreasing the production of ozone precursors (Cao et al. 2021), and 3D urban building form influences the ventilation and heat dissipation of the city, accelerating or slowing down the ozone reaction rate (Li et al. 2019). Building factors have a significant impact on urban ozone pollution.

Factors influencing the seasonal and regional variation in ozone concentration

Our study found that the UOP concentrations changed substantially across different seasons (Zhou et al. 2022). The UOP was most severe in China during spring and summer, and ozone was mainly concentrated in the southern temperate zone and the northern subtropical zone (Chen et al. 2020). In spring and summer, the temperatures rebound, and the temperature difference between north and south is small, while precipitation is less in the north than in the south, and experiences longer daylight hours, making UOP concentrated in this region. Precipitation has purified ozone concentrations, whereas high temperatures and intense illumination are sufficient to accelerate ozone production (Mao et al. 2020). Meanwhile, there are many industrial production bases in the southern temperate zone and northern subtropical zone, among which the Bei**g-Tian**-Tangshan industrial zone and the Yangtze River Delta urban agglomeration are industrial agglomerations(Yang et al. 2022). Industrial emissions produce many ozone precursors, which generate ozone under photochemical action and cause severe ozone pollution (Wang et al. 2022b). During autumn and winter, UOP concentrations changed nationwide owing to temperature effects. Ozone concentrations in temperate regions fall to the lowest point of the year (Shen et al. 2022), while UOP concentrations in the southern subtropical region and in the south increase, and the urban agglomeration of the Pearl River Delta becomes an ozone center in winter. Urbanization has led to industrialization and transportation development. The influx of large industrial aggregations and populations has caused an increase in industrial emissions and vehicle emissions. Ozone pollution is the most severe in this region, as such emissions provide many precursors for the formation of ozone pollutants (Symonds and Moussalli 2011; Zhou et al. 2022).

The relationship between ozone concentration and city class also varied with season. In spring and summer, ozone concentrations increase with urban size. However, the ozone concentration decreased in autumn and winter, with increasing urban size. On the one hand, urbanization has attracted large amounts of industry and population, leading to ozone pollution from industrial and vehicle emissions (Zhang et al. 2022a). On the other hand, in autumn and winter, straw burning in rural and suburban areas causes ozone pollution in urban centers. In contrast, urban areas in small cities are closer to rural areas and are more vulnerable than larger cities (Zhang et al. 2019).

The relative importance of building factors varied significantly between seasons; For example, building factors had the most significant effect on ozone concentrations, with 2D building factors being the dominant factor in the spring and 3D building factors being the dominant factor in the winter, but the factors that had the greatest effect in each season were temperature, precipitation, or population density. HBR was positively correlated with ozone concentrations during the summer months and negatively correlated with ozone concentrations during the other seasons. These results indicate that both 3D urban characteristics and climatic conditions cannot be ignored when conducting urban planning. The relative contribution of architectural factors to ozone concentration is influenced by both natural and anthropological factors, and the climatic and anthropological factors of the city should be taken into full consideration when urban planning is carried out. In summer, the effect of HBR on ozone concentration shows a clear positive correlation different from other seasons. Because HBR represents the ratio of high-rise buildings in a city and represents the level of urban economic development, the larger the HBR is, the more high-rise buildings there are in a city, and the higher the level of urban economic development (Huang et al. 2022). In summer, ozone concentration is most significantly affected by natural factors, traffic and population, and building factors have the lowest relative influence on ozone concentration. Most Chinese cities have the highest ozone concentrations in summer, and the more economically developed the city is, the more serious the ozone pollution. At the same time, most cities in China have the smallest shaded area of the year in the summer, weakening the shading effect and adding to the ozone response.

In general, although the explanatory power of the building factor is influenced by other factors that change with the seasons, the explanatory power of ozone concentration has been dominant among many factors and has an important influence on ozone concentration. Building height and building density reflect the 3D building form of the city, whereas the 2D building form is more represented by urban building coverage (Yuan et al. 2019; Hu et al. 2020). Although studies have compared the effects of 3D and 2D building indicators on air pollutants (Lu et al. 2016; Li et al. 2019), from the perspective of seasonal changes, the explanatory power of 3D and 2D indicators on ozone concentration also shows different explanatory power depending on the season because the natural factors and human factors on the generation, diffusion, and weakening effects of ozone concentration vary with season. Therefore, cities must plan their urban layout according to their geographical location and climatic conditions.

Limitations and prospects

This study has some limitations. The resolution of the ozone data in our study was 10 × 10 km, which may not be an accurate representation of urban ozone. There is an error in the actual ozone concentration in the urban study area, which may affect the correlation between the building morphology metrics and the UOP concentration. Due to the limited sample of cities selected for the preliminary study, we analyzed the effects of building factors on UOP by focusing on the effects of seasonal variations and simplifying the effects of regional variations on UOP.

The influence of building metrics on ozone concentrations is not only the relationship between density and height, as described in our study, but is also influenced by a range of factors, such as building shape and spatial building pattern. Building 3D indicators only provides a new perspective for studying urban buildings, and many more complex factors govern ozone dispersion, transport, and transformation. Urban green spaces and tree species could also contribute to O3 pollution via BVOCs efflux and direct leaf absorption (Paoletti 2009; Sicard et al. 2018). A new criteria and method has been developed for selecting urban trees to reduce increasing ozone levels in cities (Sicard et al. 2018).

Therefore, in future studies, the precision of ozone data should be improved to reduce the error between building data and actual buildings, and to reflect the influence of building indicators on air quality more accurately. Including green space will improve urban forest-based natural solution development (Wang et al. 2022a). The height and density of buildings can reflect the 3D shape of a city, and the impact of building factors on ozone concentration can be affected by different seasons and spatial locations. Therefore, in future studies, it is important to pay attention not only to seasonal variations but also to the influence of regional factors on UOP. Urban planners should tailor urban planning to reduce the levels of air pollutants in cities.

Conclusions

This study examined the spatial and temporal variation in ozone concentrations from the perspective of urban building morphology and investigated the effects of natural and anthropogenic factors on ozone concentrations. The main findings are as follows.

  1. (1)

    The average building density and height were 0.18 and 15.69 m, respectively, in China. Taller buildings and high densities were mostly found in Southwestern China, particularly in larger cities. In addition, we found that China's urban morphology in most (53%) cities was dominated by MRMD (28%) and MRHD (25%).

  2. (2)

    Urban ozone pollution was the most severe in summer, especially in the southern temperate zone. However, in winter, higher UOP concentrations were observed in the southern subtropical zone. Urban ozone concentrations vary considerably across cities of different sizes. In spring and summer, UOP concentrations increased with city size; in winter, UOP concentrations were the highest in small cities. We also found that UOP concentrations varied across different urban morphologies, and the highest urban ozone concentration was found in cities with LRHD.

  3. (3)

    Anthropogenic factors were the main factors influencing ozone concentration, and their influence was more than 55%, with urban morphology accounting for 42%. 2D building factors were the main factors in spring and summer, while 3D building factors were the main factors in autumn and winter.

With rapid urbanization, the number of urban buildings will continue to increase, and urban ozone pollution will become more severe. Our study deepens the understanding of the influence of urban buildings on ozone concentrations and provides guidance to governments and policy-makers for urban planning to ameliorate urban ozone pollution.