This study investigated the seasonal variation and chemical characteristics of atmospheric PM_2.5 at an urban site in Hanoi City of Vietnam in summer (July 2020) and winter (January 2021) periods. The study results showed that the average value of daily PM_2.5 concentrations observed for the winter period was about 3 times higher than the counterpart for the summer period. The concentrations of major species in atmospheric PM_2.5 (SO₄²⁻, NH₄⁺, K⁺, OC and EC) measured during the winter period were also significantly higher than those during the summer period. The contribution of secondary sources to the measured OC (the largest contributor to PM_2.5) was larger than that of primary sources during the winter period, compared to those in the summer period. The correlation analysis among anions and cations in PM_2.5 suggested that different sources and atmospheric processes could influence the seasonal variations of PM_2.5 species. The unfavorable meteorological conditions (lower wind speed and lower boundary layer height) in the winter period were identified as one of the key factors contributing to the high PM_2.5 pollution in this period. With the predominance of north and northeast winds during the winter period, the long-range transport of air pollutants which emitted from the highly industrialized areas and the intensive fire regions in the southern part of China and Southeast Asia region were likely other important sources for the highly elevated concentrations of PM_2.5 and its chemical species in the study area.

This study proposes a building energy element technology system that addresses cooling loads, in response to rising average temperatures due to global warming caused by climate change. The study analyzes performance variations and energy-saving potential based on design parameters of individual element technologies, utilizing both simulation and field demonstration to derive an integrated Cooling Load Package System (CPS). The methodology comprises three key steps: (1) identifying and selecting element technologies suitable for optimal building design under subtropical climate conditions, (2) employing the building energy simulation software EnergyPlus v9.6.0 to evaluate the energy performance of each technology and establish prioritization based on energy-saving potential, and (3) conducting local climate validation through the construction of an outdoor demonstration site in northern Vietnam to assess the real-world energy-saving effectiveness of the proposed CPS.