title: Do green spaces affect the spatiotemporal changes of PM2.5in Nanjing?
abstract: BACKGROUND
  Among the most dangerous pollutants is PM2.5, which can directly pass through human lungs and move into the blood system. The use of nature-based solutions, such as increased vegetation cover in an urban landscape, is one of the possible solutions for reducing PM2.5concentration. Our study objective was to understand the importance of green spaces in pollution reduction.
  
  
  METHODS
  Daily PM2.5concentrations were manually collected at nine monitoring stations in Nanjing over a 534-day period from the air quality report of the China National Environmental Monitoring Center (CNEMC) to quantify the spatiotemporal change of PM2.5concentration and its empirical relationship with vegetation and landscape structure in Nanjing.
  
  
  RESULTS
  The daily average, minimum, and maximum PM2.5concentrations from the nine stations were 74.0, 14.2, and 332.0 μg m-3, respectively. Out of the 534 days, the days recorded as "excellent" and "good" conditions were found mostly in the spring (30.7 %), autumn (25.6 %), and summer (24.5 %), with only 19.2 % of the days in the winter. High PM2.5concentrations exceeding the safe standards of the CNEMC were recorded predominately during the winter (39.3-100.0 %). Our hypothesis that green vegetation had the potential to reduce PM2.5concentration was accepted at specific seasons and scales. The PM2.5concentration appeared very highly correlated (R2> 0.85) with green cover in spring at 1-2 km scales, highly correlated (R2> 0.6) in autumn and winter at 4 km scale, and moderately correlated in summer (R2> 0.4) at 2-, 5-, and 6-km scales. However, a non-significant correlation between green cover and PM2.5concentration was found when its level was >75 μg m-3. Across the Nanjing urban landscape, the east and southwest parts had high pollution levels.
  
  
  CONCLUSIONS
  Although the empirical models seemed significant for spring only, one should not devalue the importance of green vegetation in other seasons because the regulations are often complicated by vegetation, meteorological conditions, and human activities.
authors: International Center for Ecology, Meteorology, and Environment, Nanjing University of Information Science and Technology, Nanjing, 210044 China ; CGCEO/Geography, Michigan State University, East Lansing, MI 48824 USA ; Department of Geography, Michigan State University, 1405 S. Harrison Road, East Lansing, MI 48823 USA.
authors: Jiquan
authors: J
authors: Chen
authors: International Center for Ecology, Meteorology, and Environment, Nanjing University of Information Science and Technology, Nanjing, 210044 China.
authors: Liuyan
authors: L
authors: Zhu
authors: School of Planning, Design, and Construction, Michigan State University, East Lansing, MI 48824 USA ; CGCEO/Geography, Michigan State University, East Lansing, MI 48824 USA.
authors: Peilei
authors: P
authors: Fan
authors: Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101 China.
authors: Li
authors: L
authors: Tian
authors: Department of Scienze Agro-Ambientali e Territoriali, University of Bari, Bari, 70126 Italy ; CGCEO/Geography, Michigan State University, East Lansing, MI 48824 USA.
authors: Raffaele
authors: R
authors: Lafortezza
keywords: Edge density; Green space; Nanjing; Nature-Based Solution (NBS); PM2.5; Pollution control; Seasonal variation