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With the acceleration of urbanization, industrial prosperity and economic development, China has attracted great attention as one of the largest sources of nitrogen dioxide (NO 2) pollution in Asia. Many studies have carried out on the source analysis, spatial and temporal distribution, physical and chemical properties of pollutants. However, there are a few studies on the high-resolution spatial distribution of atmospheric pollutants in small-scale cities, especially by using land use regression (LUR) model. LUR model is a common method for predicting the spatial variation of pollutants. It expresses spatially local changes in the results through potential variables in the equation, thus fully reflecting the spatial differentiation of small-scale pollutant concentrations. In our study, along with 40 types potential predictor, we used LUR model to simulate the concentration of NO 2 in Xi'an and to generate a high-resolution spatial distribution map of the concentrations, to provide better support for health risk assessment. In addition to using traditional predictors, due to the different classifications of roads in our study area, the use of road length as a predictor did not reflect traffic volumes well. For this reason, we weighted the roads with grades and calculated their area to fit the model. The results show that the fitting effect of the model in this study is good (adjusted R2 > 0.85), and the deviation (<2.27%) and LOOCV RMSE (<2.22 μg/m³) are both small for all time periods. Compared with traditional interpolation models, the LUR model has better prediction accuracy and greater ability to express spatial differences. Using a grid of 500 m * 500 m, 3494 grids were defined in Xi'an to simulate the spatial distribution of NO 2 concentrations. High NO 2 values appeared around the factory and represented the highest health risk. Due to abundant surface vegetation coverage, the concentrations of NO 2 and the consequent health risks in tourist spots, parks and universities were low. Image 1 • Land use regression models of NO 2 were produced for Xi'an. • Road length was weighted by different grades to express vehicle exhaust. • Industrial emissions and green plants had great impact on NO2. • The results were good, deviations and LOOCVRMSE were both small in all periods. • Health risk of children (8–10 years old) was the highest in all functional areas. [ABSTRACT FROM AUTHOR]

Carbonyl compounds are important precursors of free radicals, ozone (O 3), and secondary organic aerosols (SOA) in the atmosphere. Biomass burning is an important source of carbonyl compounds. To explore the formation pathway of carbonyl compounds from biomass burning and the effects of fuel composition and burning conditions, this study performed tube-furnace combustion experiments using three biomass types (rice straw, pine, and poplar) and their three component extracts (cellulose, hemicellulose, and lignin) at seven ignition temperatures (300–900 °C, 100 °C gradient) and two oxygen concentrations (21% and 10.5%). The results showed that the average emission factors of carbonyl compounds (EF CC) from rice straw, pine, and poplar were 2.28 ± 1.72, 3.09 ± 2.98, and 2.90 ± 2.78 g/kg, respectively. EF CC were significantly higher (5.37 ± 0.25 g/kg) in lower temperature (300–500 °C) stage than in higher temperature (0.55 ± 0.03 g/kg). Furthermore, oxygen reduction promoted the emission of carbonyl compounds, increasing the EF CC by 21.6% on average. The average EF CC for the three components of biomass decreased in the order of cellulose (3.78 ± 3.90 g/kg), hemicellulose (2.90 ± 2.60 g/kg) and lignin (1.98 ± 1.72 g/kg), and their CCs profiles were also different. Cellulose and hemicellulose produced more formaldehyde and acetaldehyde than lignin, contributing 71.1 ± 12.6%, 69.0 ± 4.4% and 62.4 ± 15.5% in CCs, respectively. Acetone was mainly produced by the combustion of hemicellulose and lignin. Aromatic aldehydes were mainly produced by lignin burning, and also were significantly affected by temperature, the proportion under higher temperature is 2.7 times that under lower temperature. The EF CC values by weighted average calculation from the three components were good matched with those of parent fuels (r = 0.98), while the fitting results for those species such as aromatic aldehydes were relatively weak (r = 0.66), showing that there are different formation pathways and sensitivity to fuel composition and burning condition among different CCs. [Display omitted] • Emission factors(EF) and compositions of 19 carbonyls are quantified from the combustion of cellulose, hemicellulose and lignin. • The formation pathways of carbonyl compounds under various conditions are discussed. • The calculated EFs of carbonyls from the three components are good agreement with parent fuels. [ABSTRACT FROM AUTHOR]