Spatiotemporal Characteristics of Particulate Matter and Dry Deposition Flux in the Cuihu Wetland of Beijing

PM2.5 Pollution Strongly Predicted COVID-19 Incidence in Four High-Polluted Urbanized Italian Cities during the Pre-Lockdown and Lockdown Periods

BACKGROUND

The coronavirus disease in 2019 (COVID-19) heavily hit Italy, one of Europe's most polluted countries. The extent to which PM pollution contributed to COVID-19 diffusion is needing further clarification. We aimed to investigate the particular matter (PM) pollution and its correlation with COVID-19 incidence across four Italian cities: Milan, Rome, Naples, and Salerno, during the pre-lockdown and lockdown periods.

METHODS

We performed a comparative analysis followed by correlation and regression analyses of the daily average PM10, PM2.5 concentrations, and COVID-19 incidence across four cities from 1 January 2020 to 8 April 2020, adjusting for several factors, taking a two-week time lag into account.

RESULTS

Milan had significantly higher average daily PM10 and PM2.5 levels than Rome, Naples, and Salerno. Rome, Naples, and Salerno maintained safe PM10 levels. The daily PM2.5 levels exceeded the legislative standards in all cities during the entire period. PM2.5 pollution was related to COVID-19 incidence. The PM2.5 levels and sampling rate were strong predictors of COVID-19 incidence during the pre-lockdown period. The PM2.5 levels, population's age, and density strongly predicted COVID-19 incidence during lockdown.

CONCLUSIONS

Italy serves as a noteworthy paradigm illustrating that PM2.5 pollution impacts COVID-19 spread. Even in lockdown, PM2.5 levels negatively impacted COVID-19 incidence.

Removal ability of different underlying surfaces to near-surface particulate matter

Atmospheric particulate matter is a wide-ranging environmental pollutant that can cause serious harm and poses a serious threat to public health. In this study, the near-surface particulate matter removal ability was quantitatively analyzed and compared for different land types under different pollution levels. The results showed that the concentrations of particulate matter 10 μm or less in diameter (PM10) and 2.5 μm or less in diameter (PM2.5) were higher in the morning and lower in the afternoon and that the seasonal variation was autumn > winter > spring > summer at a forest site. The diurnal concentration of particulate matter at a wetland site decreased continuously, with a seasonal variation of winter > autumn > spring > summer. The annual variation in the particulate matter concentration was higher in 2017 than in 2016 at both the forest and wetland sites. Forests remove particulate matter via plant leaves and root absorption, and wetlands rely on the enhancement of the relative air humidity to promote the absorption and accumulation of particles. For different air pollution levels, the deposition flux of PM2.5 increased with the pollution gradient. For the same air quality pollution level, the deposition flux of PM2.5 at the forest site was approximately 1.29 times higher than that at the wetland site. Data concerning PM10 in forests and wetlands are lacking. The results show that the deposition effect of the forest on particulate matter was better than that of the wetland.

Assessing the spatiotemporal characteristics of dry deposition flux in forests and wetlands

Forests and wetlands, as two important ecosystems, play a crucial role in reducing the concentration of particulate matters. The main purpose of this study is to reveal the contribution of forest and wetland ecosystems to the reduction of particulate matter. We collected the concentration and meteorological data during the daytime in a forest and a wetland in the Olympic Park in Beijing. The main results are as follows: daily variation in the PM₁₀ and PM_2.5 concentration had the similar trend with the lowest value at midday and relatively high values in the morning and at nightfall. In the forest ecosystem, the trend of PM₁₀ concentration at three heights followed the order: 6 m > 10 m > 1.5 m, while that of the PM_2.5 followed the order 1.5 m > 10 m > 6 m. In the wetland, PM₁₀ and PM_2.5 concentrations at the three heights exhibited the same trend: 10 m > 1.5 m > 6 m. It is a comprehensive impact on concentration which may include vegetation collection rate, meteorological conditions and some kind of human activities. The PM deposition velocity of wetland was higher than that of forest, and showed the highest values in winter both in PM_2.5 and PM₁₀. The PM deposition flux in wetland was lower than forest only in autumn, and the value of deposition flux was higher than forest in other seasons. PM concentrations was positively correlated with relative humidity but negatively correlated with temperature and wind velocity.

Effect of the wetland environment on particulate matter and dry deposition

In Beijing, particulate matter (PM) in the atmosphere, especially PM_2.5 and PM₁₀, have attracted public attention because of its adverse effects. A series of studies have investigated the sources and spatial-temporal variation of PM. Wetland has been reported to own the capacity of resolving air problem. To examine the characteristics of the particulate matter in wetlands, the diurnal variation of PM_2.5 and PM₁₀ concentrations with respect to two heights (i.e. 1.5 and 10 m, respectively) and three meteorological factors (i.e. wind speed, temperature, and relative humidity, respectively) was monitored in the Cuihu National Wetland Park in Beijing, and the dry deposition velocity and flux were analysed using the above-mentioned data. Results indicated that (1) As for diurnal variation, the PM concentration constantly decreased at 07:00-16:00 and gradually increased at 16:00-18:00. The maximum instantaneous concentration was observed at 07:00-10:00, while the minimum instantaneous concentration was observed at 13:00-16:00. (2) The annual concentration variation of PM followed the order of dry period > wet period > normal period. (3) The particulate concentrations at 10 m were always greater than those at 1.5 m. (4) The PM concentration was positively correlated to the relative humidity and negatively correlated to the temperature. Wind speed exhibited a complex effect on PM concentration. (5) The regulation of dry deposition efficiency followed the order of spring > winter > summer. (6) Wind speed strongly and positively affected the dry deposition velocity of PM10. The effects of temperature and relative humidity on dry deposition were uncertain.

Microbial communities in the tropical air ecosystem follow a precise diel cycle

This manuscript describes a precise diel cycle carried out by airborne microbiota in the tropics. 795 metagenomes from air samples taken from a single site show that fungi, bacteria, and plants all adhere to a specific timing for their presence in the near-surface atmosphere. The airborne community composition thereby shows an unexpected robustness, with the majority of the dynamics in taxa composition occurring within 24 h, but not across days, weeks, or months. Environmental parameters are the main drivers for the observed phenomenon, with temperature being the most important one.

The atmosphere is vastly underexplored as a habitable ecosystem for microbial organisms. In this study, we investigated 795 time-resolved metagenomes from tropical air, generating 2.27 terabases of data. Despite only 9 to 17% of the generated sequence data currently being assignable to taxa, the air harbored a microbial diversity that rivals the complexity of other planetary ecosystems. The airborne microbial organisms followed a clear diel cycle, possibly driven by environmental factors. Interday taxonomic diversity exceeded day-to-day and month-to-month variation. Environmental time series revealed the existence of a large core of microbial taxa that remained invariable over 13 mo, thereby underlining the long-term robustness of the airborne community structure. Unlike terrestrial or aquatic environments, where prokaryotes are prevalent, the tropical airborne biomass was dominated by DNA from eukaryotic phyla. Specific fungal and bacterial species were strongly correlated with temperature, humidity, and CO₂ concentration, making them suitable biomarkers for studying the bioaerosol dynamics of the atmosphere.

Reduction of traffic-related particulate matter by roadside plants: effect of traffic pressure and sampling height

Atmospheric particulate matters (PM) caused by urban traffic system put residents' health at serious risk. As a method of phytoremediation to mitigate this risk, roadside plants show significant potential to remove PM from the air. However, the relationship between traffic pressure, height, and leaves' capturing capacity is rarely reported. In this study, two common effective roadside plants (Hedera helix, Taxus baccata) with typical leaf shapes (broad and needle-leaved) were selected to explore the foliage capacity under high, middle and low traffic burden. A green wall covered by H. helix was tested to find out the relationship between heights and the amount of accumulated PM. Although the PM capturing capacity varied between different traffic pressures, needle-leaved species generally accumulated more PM than broad-leaved species. For PM₁₀ capturing, needle-leaved species showed higher capacity under all traffic pressures except under the low traffic pressure. For PM_2.5 capturing, needle-leaved species accumulated more PM only under the high traffic pressure. Needle-leaved plants were more sensitive to the change of traffic pressures, its PM capturing capacity changed notably between different traffic pressures because its leaf wax is more susceptible to be corroded. Leaf surface contact angle was slightly affected by the change of traffic pressure for broad-leaved species, but for needle-leaved species, it changed greatly. Leaf surface was the main zone for large PM capturing because the large PM was more likely to be stuck in grooves on the leaf surface, while leaf wax was mainly for fine PM absorption because PM with small sizes could adhere to the surface of the wax crystal. By comparing the amount of captured PM by leaf surface of urban roadside plants under different traffic pressures and height ranges, this study optimizes the benefits of roadside plants as traffic-related PM filter under different traffic conditions.

The Concentrations and Removal Effects of PM10 and PM2.5 on a Wetland in Beijing

Particulate matter (PM) is an essential source of atmospheric pollution in metropolitan areas since it has adverse effects on human health. However, previous research suggested wetlands can remove particulate matter from the atmosphere to land surfaces. This study was conducted in the Hanshiqiao Wetland National Nature Reserve in Beijing during 2016. The concentrations of PM10 and PM2.5 on a wetland and bare land in the park, as well as metrological data, were collected during the whole year. Based on the observed data, removal efficiency of each land use type was calculated by empirical models and the relationships between concentrations and metrological factors were also analyzed. The results indicated that: (1) In general, the PM10 and PM2.5 concentrations on the bare land surface were higher than those on the wetland surface, in both of which the highest value appeared at night and evening, while the lowest value appeared near noon. In terms of season, the average concentration of PM10 was higher in winter (wetland: 137.48 μg·m−3; bare land: 164.75 μg·m−3) and spring (wetland: 205.18 μg·m−3; bare land: 244.85 μg·m−3) in general. The concentration of PM2.5 on the wetland surface showed the same pattern, while that on the bare land surface was higher in spring and summer. (2) Concentrations of PM10 and PM2.5 were significantly correlated with the relative humidity (p < 0.01) and inversely correlated with wind speed (p < 0.05). The relationship between PM10 and PM2.5 concentrations and temperature was more complicated—it showed a significantly negative correlation (p < 0.01) between them in winter and spring, however, the correlation was insignificant in autumn. In summer, only the correlation between PM10 concentration and temperature on the wetland surface was significant (p < 0.01). (3) The dry removal efficiency of PM10 was greater than that of PM2.5. The dry removal efficiencies of PM10 and PM2.5 followed the order of spring > winter > autumn > summer on the wetland. This study seeks to provide practical measures to improve air quality and facilitate sustainable development in Beijing.

Air quality modeling for effective environmental management in the mining region

Air quality in the mining sector is a serious environmental concern and associated with many health issues. Air quality management in mining regions has been facing many challenges due to lack of understanding of atmospheric factors and physical removal mechanisms. A modeling approach called the mining air dispersion model (MADM) is developed to predict air pollutants concentration in the mining region while considering the deposition effect. The model takes into account the planet's boundary conditions and assumes that the eddy diffusivity depends on the downwind distance. The developed MADM is applied to a mining site in Canada. The model provides values for the predicted concentrations of PM₁₀, PM_2.5, TSP, NO₂, and six heavy metals (As, Pb, Hg, Cd, Zn, Cr) at various receptor locations. The model shows that neutral stability conditions are dominant for the study site. The maximum mixing height is achieved (1280 m) during the evening in summer, and the minimum mixing height (380 m) is attained during the evening in winter. The dust fall (PM coarse) deposition flux is maximum during February and March with a deposition velocity of 4.67 cm/sec. The results are evaluated with the monitoring field values, revealing a good agreement for the target air pollutants with R-squared ranging from 0.72 to 0.96 for PM_2.5, from 0.71 to 0.82 for PM₁₀, and from 0.71 to 0.89 for NO₂. The analyses illustrate that the presented algorithm in this model can be used to assess air quality for the mining site in a systematic way. Comparisons of MADM and CALPUFF modeling values are made for four different pollutants (PM_2.5, PM₁₀, TSP, and NO₂) under three different atmospheric stability classes (stable, neutral, and unstable). Further, MADM results are statistically tested against CALPUFF for the air pollutants and model performance is found satisfactory.

IMPLICATIONS

The mathematical model (MADM) is developed by extending the Gaussian equation particularly when examining the settling process of important pollutants for the industrial region. Physical removal effects of air pollutants with field data have been considerred for the MADM development and for an extensive field case study. The model is well validated in the field of an open pit mine to assess the regional air quality. The MADA model helps to facilitate the management of the mining industry in doing estimation of emission rate around mining activities and predicting the resulted concentration of air pollutants together in one integrated approach.

Comparison of dry and wet deposition of particulate matter in near-surface waters during summer

Atmospheric particulate matter (PM) deposition which involves both dry and wet processes is an important means of controlling air pollution. To investigate the characteristics of dry and wet deposition in wetlands, PM concentrations and meteorological conditions were monitored during summer at heights of 1.5 m, 6 m and 10 m above ground level at Cuihu Wetland (Beijing, China) in order to assess the efficiency of PM2.5 (particles with an aerodynamic size of <2.5 μm) and PM10 (particles with an aerodynamic size of <10 μm) removal. The results showed: Daily concentrations of PM, dry deposition velocities and fluxes changed with the same variation trend. The daily average deposition velocity for PM10 (3.19 ± 1.18 cm·s-1) was almost 10 times that of PM2.5 (0.32 ± 0.33 cm·s-1). For PM2.5, the following dry deposition fluxes were recorded: 10 m (0.170 ± 0.463 μg·m-2·s-1) > 6 m (0.007 ± 0.003 μg·m-2·s-1) > 1.5 m (0.005 ± 0.002 μg·m-2·s-1). And the following deposition fluxes for PM10 were recorded: 10 m (2.163 ± 2.941 μg·m-2·s-1) > 1.5 m (1.565 ± 0.872 μg·m-2·s-1) > 6 m (0.987 ± 0.595 μg·m-2·s-1). In the case of wet deposition, the relative deposition fluxes for PM2.5 and PM10 were 1.5 m > 10 m > 6 m, i.e. there was very little difference between the fluxes for PM2.5 (0.688 ± 0.069 μg·m-2·s-1) and for PM10 (0.904 ± 0.103 μg·m-2·s-1). It was also noted that rainfall intensity and PM diameter influenced wet deposition efficiency. Dry deposition (63%) was more tilted towards removing PM10 than was the case for wet deposition (37%). In terms of PM2.5 removal, wet deposition (92%) was found to be more efficient.

Population stress: A spatiotemporal analysis of population change and land development at the county level in the contiguous United States, 2001-2011

The past century has witnessed rapidly increasing population-land conflicts due to exponential population growth and its many consequences. Although the measures of population-land conflicts are many, there lacks a model that appropriately considers both the social and physical contexts of population-land conflicts. In this study we introduce the concept of population stress, which identifies areas with populations growing faster than the lands available for sustainable development. Specifically, population stress areas are identified by comparing population growth and land development as measured by land developability in the contiguous United States from 2001 to 2011. Our approach is based on a combination of spatial multicriteria analysis, zonal statistics, and spatiotemporal modeling. We found that the population growth of a county is associated with the decrease of land developability, along with the spatial influences of surrounding counties. The Midwest and the traditional "Deep South" counties would have less population stress with future land development, whereas the Southeast Coast, Washington State, Northern Texas, and the Southwest would face more stress due to population growth that is faster than the loss of suitable lands for development. The factors contributing to population stress may differ from place to place. Our population stress concept is useful and innovative for understanding population stress due to land development and can be applied to other regions as well as global research. It can act as a basis towards developing coherent sustainable land use policies. Coordination among local governments and across different levels of governments in the twenty-first century is a must for effective land use planning.

Relationships of relative humidity with PM2.5 and PM10 in the Yangtze River Delta, China

Severe particulate matter (PM, including PM_2.5 and PM₁₀) pollution frequently impacts many cities in the Yangtze River Delta (YRD) in China, which has aroused growing concern. In this study, we examined the associations between relative humidity (RH) and PM pollution using the equal step-size statistical method. Our results revealed that RH had an inverted U-shaped relationship with PM_2.5 concentrations (peaking at RH = 45-70%), and an inverted V-shaped relationship (peaking at RH = 40 ± 5%) with PM₁₀, SO₂, and NO₂. The trends of polluted-day number significantly changed at RH = 70%. The very-dry (RH < 45%), dry (RH = 45-60%) and low-humidity (RH = 60-70%) conditions positively affected PM_2.5 and exerted an accumulation effect, while the mid-humidity (RH = 70-80%), high-humidity (RH = 80-90%), and extreme-humidity (RH = 90-100%) conditions played a significant role in reducing particle concentrations. For PM₁₀, the accumulation and reduction effects of RH were split at RH = 45%. Moreover, an upward slope in the PM_2.5/PM₁₀ ratio indicated that the accumulation effects from increasing RH were more intense on PM_2.5 than on PM₁₀, while the opposite was noticed for the reduction effects. Secondary transformations from SO₂ and NO₂ to sulfate and nitrate were mainly responsible for PM_2.5 pollution, and thus, controlling these precursors is effective in mitigating the PM pollution in the YRD, especially during winter. The conclusions in this study will be helpful for regional air-quality management.

Multi-scale comparison of the fine particle removal capacity of urban forests and wetlands

As fine particle (FP) pollution is harmful to humans, previous studies have focused on the mechanisms of FP removal by forests. The current study aims to compare the FP removal capacities of urban forests and wetlands on the leaf, canopy, and landscape scales. Water washing and scanning electron microscopy are used to calculate particle accumulation on leaves, and models are used to estimate vegetation collection, sedimentation, and dry deposition. Results showed that, on the leaf scale, forest species are able to accumulate more FP on their leaf surface than aquatic species in wetlands. On the canopy scale, horizontal vegetation collection is the major process involved in FP removal, and the contribution of vertical sedimentation/emission can be ignored. Coniferous tree species also showed stronger FP collection ability than broadleaf species. In the landscape scale, deposition on the forest occurs to a greater extent than that on wetlands, and dry deposition is the major process of FP removal on rain-free days. In conclusion, when planning an urban green system, planting an urban forest should be the first option for FP mitigation.

Particle removal by vegetation: comparison in a forest and a wetland

Vegetation collection is one of the most effective scavenging methods but relevant studies are limited. It can be described by some abstract parameters such as collection rates and deposition fluxes within the canopy. In order to estimate the dry deposition within the canopy of particular matters (PMs) in Beijing, a highly particle-polluted city, and reveal the PM pollution-removal abilities of plants in wetlands and forests, concentration and meteorological data were collected during the daytime in an artificial forest and a wetland in the Olympic Park in Beijing. The dry depositions within the canopy and vegetation collection rates were calculated by a well-developed model and validated by measured deposition fluxes in 11 random experiment days. The experiment year was divided into three plant growth stages based on canopy density, and the day was divided into four different times. Two heights, 10 and 1.5 m, were defined in the forest while in the wetland, 0.5 and 1.5 m were defined. The results showed that in Beijing, the most severe pollution by PMs occurs in the non-leaf stage (NS), and the full-leaf stage (FS) is the cleanest stage. In NS, namely winter, more fossil fuel was used for worms in Beijing and peripheral areas and this might be the reason for the serious pollution condition. Within the canopy, PM deposition fluxes in the wetland are more than those in the forest, but the vegetation collection rates of the forest are higher. The lower temperature conditions led to more dry deposition, and the larger canopy contributed to the higher collection rates. During the daytime, over the year, the deposition of PM₁₀ in three plant growth stages is NS ≥ half-leaf stages (HS) ≥ FS, whereas the deposition of PM_2.5 is NS ≥ FS ≥ HS, and during the daytime, the maximum deposition fluxes occur in 6:00-9:00 in the wetland while the minimum deposition values occur in 15:00-18:00. This phenomenon was related to the temporal variation of particle concentration.