[Change Characteristics of Carbonaceous Aerosol in Chengdu from 2018 to 2021].

Carbonaceous aerosol is an important component of atmospheric fine particulates （PM2.5） that has an important effect on global climate change, atmospheric visibility, regional air quality, and human health. In order to investigate the long-term change characteristics of carbonaceous aerosols under the background of emission reduction, the concentrations of organic carbon （OC）, elemental carbon （EC） in PM2.5 samples, and volatile organic compounds （VOCs） in Chengdu from 2018 to 2021 and the corresponding meteorological factors were obtained through real-time online monitoring. The results showed that the average ρ（OC） and ρ（EC） during the monitoring period were （10.9 ±5.7） µg·m-3 and （2.6 ±1.9） µg·m-3, accounting for 25.2% and 6.0% of PM2.5, respectively, and the average ρ（SOC） was （5.7 ±3.3） µg·m-3, accounting for 52.9% of OC. The concentrations of OC, EC, and PM2.5 showed a downward trend from 2018 to 2020 [PM2.5： The concentration of average annual decrease was -7.1 µg·ï¼ˆm3·a） -1, with an average annual decrease of -14.6 %·a-1； OC： -1.7 µg·ï¼ˆm3·a）-1, -14.2 %·a-1； EC： -0.1 µg·ï¼ˆm3·a）-1, -4.4 %·a-1], and the concentrations of each pollutant in 2021 rebounded in different ranges compared with those in 2020. The concentrations of PM2.5 and OC were as follows： winter > spring > autumn > summer, and the concentrations of EC were as follows： winter > autumn > spring > summer. The proportions of OC and EC were higher in summer and autumn than in other seasons, with the average proportions of 26.8% and 6.9%, respectively. With the aggravation of the pollution level, OC, EC, and SOC concentrations gradually increased, but the proportions in PM2.5 showed a gradual downtrend, indicating that the control factor of PM2.5 pollution in Chengdu was not the carbon component. Source apportionment results showed that carbonaceous aerosols in Chengdu were mainly affected by motor vehicles, industrial sources, biomass combustion sources, and VOCs secondary reaction. From 2019 to 2021, EC was affected by the characteristic components of motor vehicles and decreased yearly. OC and EC were affected by VOCs more in spring and autumn than in other seasons. VOCs emission management should be increased in spring and autumn to reduce the impact of secondary reaction.

[Analysis of the Impact of Fireworks on Air Quality During the Spring Festival in Chengdu from 2019 to 2022].

Based on the observation data of air quality and PM2.5 components, the influence of fireworks on pollutant concentrations, PM2.5 components, and secondary transformation during the Spring Festival period from 2019 to 2022 in Chengdu were analyzed. The results indicated that the fireworks had a greater impact on the concentration of SO2, PM2.5, and PM10 than the other pollutants. During the centralized discharge of fireworks from 2019 to 2022, the average hourly concentrations of SO2, PM2.5, and PM10 increased by 6.7, 105.0, and 117.4 µg·m-3, with an increase of 135%, 236%, and 203%, respectively. During the centralized discharge period of fireworks, the contributions of fireworks to the SO2, PM2.5, and PM10 concentration were 10.0%-34.0%, 28.1%-31.3%, and 27.8%-34.6%, respectively. The impact time of fireworks on air quality decreased slightly, from 42 h in 2019 to 38 h in 2022; however, the impact on PM2.5 concentration fluctuated, and the impact in 2022 was similar to that in 2019. The main components of fireworks were K, Cl, Al, K+, and Cl-; the concentrations of these components were high and increased rapidly during the concentrated discharge, accounting for 5%-18% of PM2.5, with an increase rate of 87%-1511%. The discharge of fireworks had little effect on NH4+, V, Cd, and Co, and the variation range was within±20%. Throughout the pollution period during the Spring Festival, the mass concentrations of the main components of fireworks were 4.9-31.7 times and 7.4-68.2 times that of the heavy pollution and good weather before the Spring Festival, and their proportions increased by 4%-8%. Secondary sources; fireworks; and biomass burning, coal burning, and industry were the main sources of PM2.5 during the 2019-2022 Spring Festival. The contribution rate of fireworks and biomass combustion was 13%-25%, with higher contribution rates in 2019 and 2022. From the perspective of the impact of meteorological conditions on fireworks discharge, high humidity, low wind speed, and low temperature will intensify the impact of firework discharge on air quality and vice versa. Wind speed mainly affected Al, K+, Cl-, and SO42-, whereas relative humidity mainly affected secondary components such as NO3- and NH4+.

[Analysis of Characteristics of Water-soluble Ions in PM2.5 in Chengdu Based on the MARGA].

Water-soluble ions in PM2.5 were serially on-line monitored using the MARGA sampling and measurement system in Chengdu in 2019. Pollution characteristics of water-soluble ions were analyzed using the meteorological monitoring data. The results show that variations in the concentrations of eight water-soluble ions were consistent with the variations in PM2.5 in Chengdu. The annual average mass concentration of the total water-soluble ions was (20.2±12.7) µg ·m-3, accounting for 48.6% of the PM2.5 mass, which indicates that water-soluble ions were the major components of PM2.5. The mass concentrations of all the ions were in the order of NO3- > SO42- > NH4+ > Cl- > Ca2+ > K+ > Mg2+ > Na+. The annual average mass concentration of secondary ions was (20.2±12.7) µg ·m-3, accounting for 87.2% of total water-soluble ions. The concentrations of total water-soluble ions in different seasons were in the order of winter > spring ≈ autumn > summer. Monthly variations in total water-soluble ion concentrations followed a U-shaped curve; mass concentrations were the highest in January and December and lowest from June to August. Monthly variations in the concentrations of NO3-, SO42-, NH4+, Cl-, Na+, and K+ were consistent with the total water-soluble ion concentrations, while the concentrations of Ca2+ and Mg2+ were the highest in June. Visibility declined with the increase in the concentration of water-soluble ions, especially secondary water-soluble ions regardless of the rainfall. Light rain (accumulated rainfall in 24 h <10 mm) had no scavenging effect on water-soluble ions, while moderate and heavy rainfall had a significant effect. There was a significant positive correlation between NO3-, SO42-, and NH4+ (all the correlation coefficients were over 0.7), indicating that the mechanisms of evolution of secondary water-soluble ions in the atmosphere are highly similar to each other. The annual mean values of SOR and NOR were 0.42 and 0.12, respectively, which were negatively correlated with temperature and O3 and positively correlated with humidity, indicating that the main source of SO42- was heterogeneous oxidation reactions in the liquid phase and the main source of NO3- was heterogeneous oxidation reactions at night. The annual mean values of CE/AE and NR were 1.2 and 1.1, respectively, indicating that most aerosols in the study area were relatively alkaline. The atmospheric environment of Chengdu is rich in ammonia; thus, (NH4)2 SO4 and NH4NO3 were the main forms of secondary ions.

[Characteristics and Formation Mechanism of Three Haze Pollution Processes in Chengdu in Winter].

Based on the online monitoring data of gaseous pollutants and components in PM2.5 from Chengdu super observatory of atmospheric environment, the meteorological factors and component characteristics of three haze pollution process in Chengdu from 2019 to 2020 were analyzed. The CMB model was adopted to simulate the sources and variation trends of PM2.5 pollution during the study period, and the causes of each pollution process were analyzed. The results showed that all the three pollution processes occurred under adverse meteorological conditions, where the relative humidity and temperature continued to rise and the wind speed and boundary layer height continued to decrease. The average daily relative humidity was greater than 70%, average daily temperature was greater than 8℃, average daily wind speed was less than 0.8 m ·s-1, and average daily boundary layer height was less than 650 m. During the three events of pollution, the main components were NO3-, OC, NH4+, and SO42-. Among them, the mass concentration and proportion of NO3- increased by 1.47-2.09 and 0.22-0.35 times, respectively, during the pollution period as compared to those during the clean period. NO3- was a key component of PM2.5 pollution during winter in Chengdu. During the three pollution processes, the mean values of SOR and NOR were 0.40 and 0.27, respectively, and the secondary transformation degree of SO2 and NOx was high. The conversion of SO2 to SO42- was mainly dominated by heterogeneous oxidation at night, and the conversion of NOx to NO3- was dominated by heterogeneous hydrolysis. The characteristics of the three processes were slightly different. Process Ⅰ showed evident secondary nitrate-dominated characteristics. During the period of rising PM2.5 concentration in process Ⅱ, it was mainly affected by coal emissions, but during the periods of high PM2.5 concentration, it was mainly affected by NO3-. Process Ⅲ was also a nitrate-dominated process, but emissions of fossil fuel combustion had increased during certain polluted periods. Secondary nitrate, secondary sulfate, motor vehicles, and coal combustion were the main pollution sources during the study period. The PM2.5 concentration was positively correlated with the contribution of secondary nitrate and negatively correlated with the contribution of dust source.

[Emission Inventory and Characteristics of Anthropogenic Air Pollution Sources Based on Second Pollution Source Census Data in Sichuan Province].

In this research, the activity data of Sichuan Province were collected using bottom-up and top-down methods. According to the second survey of pollution sources, the activity data of industrial source includes information of 11020 boilers and 60078 industrial enterprises. Data of 19152 industrial enterprises were collected in Chengdu, accounting for 32% of the total number of enterprises in Sichuan Province. The anthropogenic air pollutant emission inventory of 9 km×9 km was developed for Sichuan Province in 2017 with the use of appropriate emission estimation methods. The results showed that the total emission of SO2,NOx,CO,PM10,PM2.5,BC,OC,VOCs, and NH3 in Sichuan were 308.6×103, 725.7×103, 3131.2×103, 927.6×103, 422.4×103, 30.2×103, 72.0×103, 600.9×103, and 887.1×103 t. The fixed combustion source and process source mainly contributed as sources of SO2. The main source of CO was the process source and mobile source. Further, the dust source and process source were the main sources of PM10 and PM2.5, and the dust source was the largest source of BC and OC contributions. The emission sources of the VOCs were primarily the process sources, mobile sources and solvent use sources. The NH3 emissions were mainly from livestock and poultry breeding and nitrogen fertilizer applications. The spatial distribution results showed that the pollutants were mainly concentrated in the densely populated Sichuan basin and Panzhihua region, where industry and agriculture were relatively developed. The high value points are concentrated along the Deyang-Chengdu-Meishan-Leshan line in Chengdu Plain. The emission inventory established in this study still has certain uncertainties, and the accuracy of activity level data acquisition should be further enhanced. Moreover, pollutant emission factor testing should be carried out for typical pollution sources, and grid emission inventory should be improved to provide scientific support for the prevention and control of air pollution in Sichuan Province in the future.

[Fine Particulate Matter Source Profile of Typical Industries in Sichuan Province].

An electrical low pressure impactor particle monitor was used to monitor typical industries in Sichuan Province, such as cement, glass, ceramic, brick-tile, coal-fired boiler, biomass boiler, power plant, and steel industry. Fine particulate matter source profiles of each industry were developed based on the laboratory analysis. The results showed that Si, Ca, and Mg were the major elements of building industry particulate matter emission. Sulfate emission from double sodium-calcium was higher than from other desulfurization technologies in the building industry. The main chemical components of PM2.5 from power plants were SO42-, Ca2+, NH4+, Mg, and Si, while OC, Al, Si, and Ca were the main chemical components of PM2.5 from coal-fired boilers. The content of OC was the most abundant in biomass briquette boiler particulate matter emissions, followed by K and EC. In term of the biomass fuel boiler PM2.5 source profile, OC, EC, and Cl- were the major chemical components. Ca was the largest component of PM2.5 from the steel industry, accounting for 18.11% of the total PM2.5 emission, followed by SO42-, Na+, and Fe.

[Agricultural Ammonia Emission Inventory and Its Spatial Distribution in Sichuan Province from 2005 to 2014].

Based on the urban activity data and emission factors, agricultural ammonia emission inventory was developed for Sichuan province from year 2005 to 2014. Meanwhile, its historical trends, spatial distribution and the relationship between agricultural ammonia emission and PM10 concentration were analyzed. The results showed that the highest emission was estimated to be 111.9×104 t in 2006, which was reduced to 95.5×104 t in 2014. The interannual variation characteristics were different for 21 cities in Sichuan, the annual emission of Chengdu, Meishan, Zigong, Luzhou, Yibin, Panzhihua, Aba and Ganzi changed largely in the study period. Livestock source and nitrogen fertilizers were the major contributors, accounting for 72%-79% and 20%-27% of the total agricultural NH3 emission respectively. Hog, poultry and cow were the major contributors under the category of livestock sources for the most cities. It's worth mentioning that rabbit was the largest contributor in Zigong, accounting for 39% of the total livestock NH3 emission. The urban and sub-urban areas of Chengdu, the northeastern and southern part of Sichuan were the hot-spots for agricultural NH3 emission. In term of spatial distribution, there were higher emissions in the east of Sichuan and other suburban and rural areas. There was a good agreement between agricultural NH3 emission and PM10 concentration, indicating agricultural NH3 emission played an important role in the particle formation.

[Emission Inventory of Crop Residues Field Burning and Its Temporal and Spatial Distribution in Sichuan Province].

Based on the collected activity data, the 2012 emission inventory of crop residues field burning in Sichuan province was developed through the emission factor approach. Besides, the temporal and spatial distribution of pollutant emissions was also analysed in this paper. The results showed that the total emissions of SO2, NO(x), NH3, CH4, NMVOC, CO, PM2.5, EC and OC from crop residues field burning in Sichuan province in the year of 2012 were 1 210, 12 185, 2 827, 20 659, 40 463, 292 671, 39 277, 1 984 and 10 215 t, respectively; The rice straw, wheat straw, corn straw and oil rape straw were four major contributors to pollutant emissions, with a total contribution about 88% - 94%; Crop residues field burning emissions were affected by agricultural harvesting. Temporally, the emissions were concentrated in July and August with a small peak in May; Spatially, the Chengdu plain, the Northern area and the Eastern area of Sichuan province were the highest emission areas, while the Western area had relatively low emissions; The key uncertain sources included emission factors and parameters used for estimating crop burning amounts.