Covid-19 lockdowns have improved the ambient air quality across the world via reduced air pollutant levels. This article aims to investigate the effect of the partial lockdown on the main ambient air pollutants and their elemental concentrations bound to PM 2.5 in Hanoi. In addition to the PM 2.5 samples collected at three urban sites in Hanoi, the daily PM 2.5 , NO 2 , O 3 , and SO 2 levels were collected from the automatic ambient air quality monitoring station at Nguyen Van Cu street to analyze the pollution level before (March 10th–March 31st) and during the partial lockdown (April 1st–April 22nd) with “current” data obtained in 2020 and “historical” data obtained in 2014, 2016, and 2017. The results showed that NO 2 , PM 2.5 , O 3 , and SO 2 concentrations obtained from the automatic ambient air quality monitoring station were reduced by 75.8, 55.9, 21.4, and 60.7%, respectively, compared with historical data. Besides, the concentration of PM 2.5 at sampling sites declined by 41.8% during the partial lockdown. Furthermore, there was a drastic negative relationship between the boundary layer height (BLH) and the daily mean PM 2.5 in Hanoi. The concentrations of Cd, Se, As, Sr, Ba, Cu, Mn, Pb, K, Zn, Ca, Al, and Mg during the partial lockdown were lower than those before the partial lockdown. The results of enrichment factor (EF) values and principal component analysis (PCA) concluded that trace elements in PM 2.5 before the partial lockdown were more affected by industrial activities than those during the partial lockdown.

The increasing demand of rice crops leads to elevated levels of nitrogen in water bodies in Asia. The concentrations of organic and inorganic nitrogen and the nitrogen isotope ratio in nitrate (NO 3 -) were analysed to identify the sources of nitrogen in the outflow waters from a paddy field in Japan in 2013. Nitrogen concentrations in the drainage and percolation waters were the highest during the paddling period, NO 3 -was the dominant form of dissolved total nitrogen and the δ 15 N-NO 3 -values in both types of water were close to that of the chemical fertilizer. During the irrigation and non-irrigation periods, NO 3 -and dissolved organic nitrogen (DON) were the dominant in percolation water, whereas DON was dominant in drainage water. The strong correlation between the δ 15 N-NO 3 -values in the irrigation and drainage water suggested that the irrigation water is one of the N sources in the drainage water during the irrigation period. Nitrate in percolation water during irrigation and non-irrigation periods might have been affected by the nitrified ammonium in the chemical fertilizer, or mineralized nitrogen in the soil or organic fertilizer.

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