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In urban North China, nitrate (NO3-) is a primary contributor to haze formation. So far, the production processes and source apportionments of atmospheric NO3- during the heating season (i.e., the wintertime) have not yet been well understood. This study determined δ15N-NO3-, δ18O-NO3-, and Δ17O-NO3 of aerosol samples to compare the potential sources and formation pathways of atmospheric NO3- during heating (November to March) and non-heating (April to May) seasons. Combining stable isotope composition with the MixSIAR model based on Δ17O-NO3- showed that NO3 + DMS/HC pathway was the dominant process of atmospheric nitrate formation during the heating season (mean = 52.88 ± 16.11%). During the non-heating season, the contributions of NO3 + DMS/HC (mean = 37.89 ± 13.57%) and N2O5 + H2O (mean = 35.24 ± 3.75%) pathways were comparable. We found that Δ17O-NO3 was negatively correlated with wind speed and positively correlated with relative humidity during the heating season, possibly associated with the sources and production of atmospheric NO3-. In specific, in a dust storm event, the very low Δ17O-NO3 is likely associated with particles from land surface. Under the premise of considering 15N fractionation, the constraint-based on δ15N-NO3- illustrated that coal combustion was the major source of NOx emission during the heating season, and the relative contribution of coal combustion decreased rapidly from the heating season (mean = 42.56 ± 15.50%) to the non-heating season (mean = 21.86 ± 4.91%). Conversely, the proportion of NOx emitted by soil microbes rose significantly from the heating (mean = 9.67 ± 5.99%) to non-heating season (mean = 24.02 ± 11.65%). This study revealed differences in the sources and formation processes of atmospheric NO3 during the heating and non-heating seasons, which are of significance to atmospheric nitrogen oxide/nitrate pollution mitigation.

The fast-growing Eucalyptus (E. Europhylla) was used as the raw materials to prepare for micro/nanocellulose fibrils. The morphology changes of cellulose by sodium hydroxide linkage ultrasonic energy treatment was discussed. The properties of treated cellulose was evaluated by X-ray , scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy. By the degree of crystallinity of the experimental test results showed that: a high concentration (17.5%, mass fraction) NaOH solution swelling with ultrosonication chemical pretreatment of cellulose prepared micro/nanofibrils change in crystal form, that is transformed cellulose I into cellulose II. However, the cellulose micro/nanofibrils remained crystalline cellulose I type after treated by a low concentration (2%, mass fraction) NaOH solution swelling with ultrosonicaion chemical pretreatment. High alkali activation sound chemical pretreatment increased the crystallinity of obtained micro/nanofibrils, the corresponding values were 89.2% and 86.3%. Observed by the scanning electron microscope that: a low concentration alkaline with ultrosonication chemical pretreatment increased the degree of sub-wire broom, the fiber surface area increased accordingly, and the fiber is more "open", so that the reaction activity of the cellulose fibers improved. The infrared spectrum showed that: the chemical changes between cellulose micro/nanofibrils and NaOH occurred after mercerization.