The first nitrous acid (HONO) observation was conducted in Kunming of Yunnan Province, from April to May 2021 with frequent ozone (O₃) pollution events. To evaluate the impact of HONO on O₃, the WRF-Chem model simulations were conducted, with two cases including or excluding potential HONO sources. Based on the comparison between simulations and the corresponding observations, it was found that the application of the MEIC inventory (version 2020) could reasonably simulate HONO, nitrogen dioxide (NO₂), O₃ and fine particulate matter (PM_2.5) in urban Kunming. The additional HONO sources noticeably enhanced atmospheric oxidation capacity in Kunming and accelerated the hydroxyl radical (OH) production rate, leading to an O₃ enhancement of (2–6)×10⁻⁹ with the corresponding percentage enhancement of 2%–8% at the Kunming site within the height of 0–4 km and an O₃ enhancement of (4–7)×10⁻⁹ near the ground at the Kunming site and its surrounding area. The O₃-VOCs-NO_x sensitivity was also influenced by the potential HONO sources. This study deepened the understanding of HONO, atmospheric oxidation capacity and O₃ formation in the Yunnan-Guizhou Plateau, and could be helpful for regional O₃ pollution control. 

To investigate the causes of ozone pollution in Kunming city during the spring season, a field atmospheric experiment was conducted at Yijingyuan Hotel, Kunming city, from April 15 to May 20, 2021. The study analyzed the variation patterns of atmospheric photochemical pollutants in Kunming city during the spring season, and a box model was utilized to simulate the local chemical generation of ozone and the sensitivity of its formation.The results showed that during the observation period, the ozone pollution precursors volatile organic compound (VOCs), nitrogen dioxide (NO₂)and carbon monoxide (CO) in Kunming increased significantly, the photochemical reaction activity was strong, and the photochemical generation played a significant role in the initiation and aggravation stages of ozone pollution. The peak values of ozone formation rate F(O₃) were close to 20×10⁻⁹ h⁻¹ and 16×10⁻⁹ h⁻¹, respectively. The results indicate that Kunming is in a VOCs-limited area. In addition to reducing anthropogenic VOCs such as alkenes and aromatics, controlling the CO concentration is also an effective way to control ozone pollution.

In order to accurately grasp the emission characteristics of anthropogenic air pollutants in Kunming, this study utilizes statistical data from the statistical yearbook and various municipal departments, integrating enterprise surveys, field sampling, and on-site interviews and investigations to establish an anthropogenic emission inventory for Kunming in 2018. The source spectrum data for volatile organic compounds (VOCs) in Kunming were obtained through emission outlet testing at key enterprises and literature research. A detailed list of VOCs sub-species in Kunming was compiled, and their ozone formation potential was calculated. The results showed that the emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_x), carbon monoxide (CO), VOCs, ammonia (NH₃), particulate matter (PM₁₀), fine particulate matter (PM_2.5), black carbon (BC) and organic carbon (OC) in Kunming during 2018 were 13476.92 tons, 53327.85 tons, 397383.83 tons, 55514.73 tons, 20465.41 tons, 75473.99 tons, 29405.57 tons, 1947.53 tons, 4405.39 tons, respectively. Among these, the primary emission sources for NO_x were mobile sources (50.7%), NH₃ were agricultural sources (88.5%), PM₁₀ were dust sources (44.1%) and process sources (43.1%). The main emission sources of CO, VOCs and PM_2.5 were process sources, which accounted for 68.2%, 41.7%, and 51.2% of the emissions of different pollutants, respectively. The primary emission sources for SO₂, BC and OC were stationary combustion sources of fossil fuel, with emission shares of 53.0%, 45.0% and 35.9%, respectively. Pollutants were mainly concentrated in the 5 districts of the main city as well as in Anning City. Within the 5 districts of the main city, pollutants were distributed outward from the center along Youth Road and Renmin Middle Road, with relatively few pollutants found in Chenggong District. SO₂, BC, and OC were mainly distributed by high-value point sources, NO_x, CO, VOCs, and PM_2.5 were distributed by a combination of line and point sources. PM₁₀ presented a spatial distribution characterized by a combination of point and surface sources. NH₃ showed a significant spatial distribution characteristics of surface sources. VOCs sub-species inventory emissions were dominated by aromatic hydrocarbons and alkanes, with the main sources being vehicle emissions and architectural coatings, as well as the industrial solvent. Ozone formation potentials (OFP) for aromatic hydrocarbons accounted for up to 49.9%, with species such as (m- and p-) xylene, toluene, and ethylene comprising a relatively high proportion of the VOCs species. 

To explore the characteristics and sources of water-soluble inorganic ions in PM_2.5 of Kunming, simultaneously on-line measurements of major water-soluble inorganic ions and gaseous pollutants were performed from April 15 to May 20, 2021 in Xishan district, Kunming city using a Gas-aerosol Collector and Ion Chromatograph (GAC-IC). The results showed that the average mass concentration of PM_2.5 was 25.0±15.0 μg/m³, indicating that the atmosphere of Kunming was at a relatively clean level, and the average mass concentration of water-soluble ions was 8.32±4.83 μg/m³, which accounted for 32.1% of the PM_2.5 concentration. The water-soluble components of PM_2.5 and gaseous precursors showed obvious diurnal variation, with the increase of inorganic ion concentrations at night and the decrease of inorganic ion concentrations during the day after reaching their peak in the morning. The average SOR and NOR were 0.55 and 0.042, indicating that there was an obvious secondary transformation process of sulfate, but not of nitrate, which might be accompanied by the formation of nitrate and the decomposition of NH₄NO₃. The result of positive matrix factorization (PMF) indicated that there were five main contribution sources of water-soluble ions in PM_2.5, which were fossil fuel combustion source and industry (36%), secondary sulfate (27%), biomass combustion (18%), secondary nitrate (16%) and sea salt (3%).

Carbon components, water-soluble ions and their gaseous precursors in atmospheric PM_2.5 in Taian were monitored online from May 10 to June 10, 2019. The mass concentration and component composition of PM_2.5 (carbonaceous species and water-soluble ions) were analyzed. The results showed that the average mass concentration of PM_2.5 was 37.7 μg/m³ during the sampling period, which was 1.1 times higher than the standardary limit (35 μg/m³) regulated by of Chinese Ambient air quality standards (GB 3095–2012). For instance, the content of water-soluble ions in PM_2.5 was the highest with 47.3%. The water-soluble components of PM_2.5 and gaseous precursors had obvious diurnal variation, with a peak (single peak) at 7:00 am. OC/EC ratio of Taian in summer ranged from 1.1 to 17.5, indicated that Taian was mainly affected by a mixture of biomass combustion, coal combustion and exhaust emissions. Positive matrix factor analysis (PMF) showed that the proportion of secondary nitrate, biomass combustion source, secondary sulfate and coal combustion soure in PM_2.5 were 22.0%, 46.7%, 29.9% and 1.4%, respectively.

In summer and winter of 2017, two self-developed blue light converter-photolytic chemiluminescence (BLC-PCL) NO_x analyzers and a traditional molybdenum-chemiluminescence (MCL) NO_x analyzer (Thermo 42i-TL) were applied for atmospheric NO_x monitoring. A performance comparison experiment for BLC-PCL and MCL NO_x analyzers was carried out during the observation period, and the numerical correction methods for possible interferences was discussed in detail. Results show that the two methods have stable measurement performance for NO (R²=0.994, slope is 0.98). The measurement of NO₂ by MCL is 25%–30% higher than that of PCL. Notably, water vapor interference can cause the NO_x signals to be underestimated by 0.2%–13.2%; photochemical interferences can lead to an underestimation of NO by 0–13.3% and an overestimation of NO₂ by 0–8.8%. These results highlight the necessity of numerical correction of such interferences and the importance to carefully design related parameters such as photolysis efficiency, pipeline residence time, and pipeline humidity control. 

This paper reviews the current status of observational studies on atmospheric formaldehyde in China, and discusses the atmospheric formaldehyde concentration levels, the relative contributions of primary and secondary sources, and the inventory of formaldehyde emissions from anthropogenic sources. On this basis, the authors point out some limitations of the existing studies and make targeted suggestions for future observational studies on formaldehyde.

VOCs concentrations based on offline sampling in Suzhou from July to October 2020 were monitored, and temporal and spatial distribution characteristics, ozone formation potential (OFP) and sources of VOCs were conducted and compared with other studies in China. The results showed that the average concentration of VOCs in Suzhou in the summer is 47.1 nL/L, the average OFP is 334.7 μg/m³, and the aromatic hydrocarbons and oxygenated organics (OVOCs) are important components of VOCs in Suzhou and contribute a lot to ozone generation. The trends of VOCs concentration and composition in Suzhou are similar with those in Shanghai. Positive matrix factorization (PMF) model results showed that six major sources of VOCs in Suzhou are liquefied petroleum gas volatilization sources (20.7%), solvent usage sources (19.5%) and industrial sources (17.5%), followed by other sources, vehicle exhaust emission sources and combustion sources, in which the contribution of liquefied petroleum gas volatilization sources is higher than the general level in Yangtze River Delta. The higher concentration of aromatic hydrocarbons in the Yangtze River Delta is related to the higher contribution of industrial and solvent uses. In general, aromatic hydrocarbons and OVOCs have a greater impact on the atmospheric environment of Suzhou. The main sources are surface coating, gas stations, traffic emission, petrochemical sources and electric heating sources, which should be mainly controlled.