Effect of NOx and RH on the secondary organic aerosol formation from toluene photooxidation

The secondary organic aerosol (SOA) formation mechanism and physicochemical properties can highly be influenced by relative humidity (RH) and NOx concentration. In this study, we performed a laboratory investigation of the SOA formation from toluene/OH photooxidation system in the presence or absence of NOx in dry and wet conditions. The chemical composition of toluene-derived SOA was measured using Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). It was found that the mass concentration of toluene decreased with increasing RH and NOx concentration. However, the change of SOA chemistry composition (f₄₄, O/C) with increased RH was not consistent in the condition with or without NOx. The light absorption and mass absorption coefficient (MAC) of the toluene-derived SOA only increased with RH in the presence of NOx. In contrast, MAC is invariant with RH in the absence of NOx. HR-ToF-AMS results showed that, in the presence of NOx, the increased nitro-aromatic compounds and N/C ratio concurrently caused the increase of SOA light absorption and O/C in wet conditions, respectively. The relative intensity of CHON and CHO_xN family to the total nitrogen-containing organic compounds (NOCs) increased with the increasing RH, and be the major components of NOCs in wet condition. This work revealed a synergy effect of NOx and RH on SOA formation from toluene photooxidation.     

Proposed performance criteria for samplers of total suspended particulate matter

In order to facilitate intercomparison of dust concentrations measured with different samplers of total suspended particulates (TSP) the following scheme is proposed: based on regressions of experimental data permitting particle size values d₈₀ and d₅₀ (d_k is the particle diameter of the aerosol mass size distribution for which k per cent of the mass comes with particles smaller than d_k) as a function of wind speed, the knowledge of the average wind speed occurring during a typical sampling interval permits an assessment of the characteristic stop distances S₅₀, S₈₀ of the aerosol to be sampled. If the samplers are characterized by the maximum particle stop distance up to which they allow representative sampling, suitable correction factors derived from S₅₀, S₈₀ allow conservative estimates of the TSP concentration.     

Ozone concentrations, flux and potential effect on yield during wheat growth in the Northwest-Shandong Plain of China

Ozone (O₃) concentration and flux (F_o) were measured using the eddy covariance technique over a wheat field in the Northwest-Shandong Plain of China. The O₃-induced wheat yield loss was estimated by utilizing O₃ exposure-response models. The results showed that: (1) During the growing season (7 March to 7 June, 2012), the minimum (16.1 ppbV) and maximum (53.3 ppbV) mean O₃ concentrations occurred at approximately 6:30 and 16:00, respectively. The mean and maximum of all measured O₃ concentrations were 31.3 and 128.4 ppbV, respectively. The variation of O₃ concentration was mainly affected by solar radiation and temperature. (2) The mean diurnal variation of deposition velocity (V_d) can be divided into four phases, and the maximum occurred at noon (12:00). Averaged V_d during daytime (6:00–18:00) and nighttime (18:00–6:00) were 0.42 and 0.14 cm/sec, respectively. The maximum of measured V_d was about 1.5 cm/sec. The magnitude of V_d was influenced by the wheat growing stage, and its variation was significantly correlated with both global radiation and friction velocity. (3) The maximum mean F_o appeared at 14:00, and the maximum measured F_o was − 33.5 nmol/(m²·sec). Averaged F_o during daytime and nighttime were − 6.9 and − 1.5 nmol/(m²·sec), respectively. (4) Using O₃ exposure-response functions obtained from the USA, Europe, and China, the O₃-induced wheat yield reduction in the district was estimated as 12.9% on average (5.5%–23.3%). Large uncertainties were related to the statistical methods and environmental conditions involved in deriving the exposure-response functions.     

Heterogeneous transformation of peroxyacetylnitrate

The heterogeneous decomposition of peroxyacetylnitrate (PAN) has been investigated using a flow reactor and infrared spectroscopic analysis. The decomposition rate in air due to glass surfaces follows the relation d[PAN]/dt = −S/V([PAN] × 7 × 10⁷ + [CH₃C(O)OO] × 5 × 90¹²)exp(−9382/T) molecules cm⁻³ s⁻¹ (S/V=surface to volume ratio). The rate observed for NH₄HSO₄-covered surfaces is lower than in the glass case. The rate is high enough to affect many laboratory experiments but too slow to have any influence on PAN decomposition under ambient conditions.     

Wintertime measurements of aerosol acidity and trace elements in Wuhan,a city in central China

A 2-week intensive ambient aerosol study was conducted in December 1988 in Wuhan (Hubei Province), a city of nearly 2 million located on the Yangtze River in central China (P.R.C.). This is an industrial region where soft coal burning is widespread, and emission controls for vehicles and industrial facilities are minimal. The sampling site was located in one of the civic centers where residential and commercial density is highest. An Andersen dichotomous sampler was operated with Teflon membrane filters to collect fine (d_p < 2.5 μmad) and coarse (2.5 ⩽ d_p < 10 μmad) particles for total mass and element determinations. An annular denuder system (ADS) was used to collect fine fraction aerosols for analyses of ionic species including strong acidity (H⁺).The study was conducted between 18 and 30 December, which was rainless, consistently cool (3–10°C) and overcast, but without fog or acute stagnation. Fine particulate mass (PM, as μ m⁻³) averaged 139 (range 54–207); coarse PM averaged 86 (range 29–179). Trace element concentrations were also high. Crustal elements (Si, Al, Ca and Fe) were found primarily in the coarse fraction, while elements associated with combustion (S, K, Cl, Zn and Se) were enriched in the fine fraction. The concentrations of arsenic and selenium were evidence of a large source of coal burning, while vanadium levels (associated with fuel oil use) were not especially enriched.Despite the seemingly high PM loadings, ionic concentrations were not especially high. The average composition of soluble fine aerosol species (in neq m⁻³) were SO₄²⁻: 520 (range 180–980), NO₃⁻: 225 (range 50–470), Cl⁻: 215 (range 20–640), and NH₄⁺: 760 (range 280–1660). A deficit in accountable FP components (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³. (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³Aerosol acidity was negligible during most monitoring periods, H⁺: 14 (range 0–50 neq m⁻³, equivalent to 0–2.5 μm m⁻³ as H₂SO₄). Sulfur dioxide, measured by the West-Gaeke method for part of the study, concentrations were low. Although not directly measured, the aerosol measurments suggested that gaseous HCl (from refuse incineration) and NH₃ (animal wastes) concentrations might have been high. Higher aerosol acidity might be expected if HCl sources were more prominent and not neutralized by local ammonia or other base components.     

BTEX pollution caused by motorcycles in the megacity of HoChiMinh

Monitoring of benzene, toluene and xylenes (BTEX) was conducted along with traffic counts at 17 roadside sites in urban areas of HoChiMinh. Toluene was the most abundant substance, followed by p,m-xylenes, benzene, o-xylene and ethylbenzene. The maximum observed hour-average benzene concentration was 254 μg/m3 . Motorcycles contributed to 91% of the traffic fleet. High correlations among BTEX species, between BTEX concentrations and the volume of on-road motorcycles, and between inter-species ratios in air and in gasoline indicate the motorcycle-exhaust origin of BTEX species. Daily concentrations of benzene, toluene, ethylbenzene, p,m-xylenes and o-xylene were 56, 121, 21, 64 and 23 μg/m 3 , respectively. p,m-xylenes possess the highest ozone formation potential among the BTEX family.     

Seasonal contrasts in modelled and observed dry deposition velocities of O3, SO2 and NO2 over three surfaces

Results of modelled and observed deposition velocities (V_d) for O₃, SO₂ and NO₂ for time-averaged diurnal cycles and sometimes for a collection of hourly values taken from different days are discussed for different seasons. From the observations, it was found that the O₃V_d values over a deciduous forest had a daytime representative value of 1.0 cm s⁻¹ in the summer and 0.3 cm s⁻¹ in the winter. For SO₂ over the same forest and over a carrot field the daytime values ranged from 0.0 to 0.65 cm s⁻¹ in the autumn, and for SO₂ over a snow surface the V_d ranged from 0.0 to 0.15 cm s⁻¹. The NO₂V_d was mostly negative over the forest and the carrot field in the autumn and had a range of 0.0-0.15 cm s⁻¹ over snow. From the model, it was found that for the three seasons the V_d values over all the land-use types were much larger than the observations. The model could not simulate the observed negative values of the NO₂V_d. The impact of the V_d model and its modified version on the concentrations of O₃ and SO₂ were tested with a comprehensive Eulerian air quality model.     

氨对甲苯二次有机气溶胶形成和化学组分的影响研究

氨(NH_3)是大气中常见的主要碱性污染气体,能够影响二次有机气溶胶(SOA)的形成和化学组分.本文利用自制的烟雾腔系统开展了NH_3对甲苯SOA形成和化学组分的影响研究,先后采用扫描移动粒径谱仪(SMPS)、气溶胶激光飞行时间质谱仪(ALTOFMS)、紫外-可见分光光度计(UV-Vis)、衰减全反射傅里叶变换红外光谱仪(ATR-FTIR)和荧光光谱仪(MF)测量反应产生的SOA粒子的物理化学性质.结果显示,在光照60 min的时间范围内,有NH_3条件下形成的SOA质量浓度和中心粒径相比于无NH_3条件下分别增加了50%和25%,这说明NH_3能够显著促进甲苯SOA的形成.与无NH_3条件下相比,NH_3存在时甲苯SOA化学组分的紫外可见吸收光谱在270 nm处有明显的吸收峰;红外吸收光谱出现了CN、C—N、N—H键的吸收峰;激光解吸附质谱图中含有m/z=67(C_3H_3N_2~+)、m/z=41(C_2H_2N~+)和m/z=28(CH2N+)碎片峰.这些谱图信息综合表明是NH_3和甲苯SOA中的二醛组分反应形成了咪唑类新产物.这为研究人为源SOA的形成机制提供了实验依据.     

典型钢铁企业VOCs污染特征及SOA生成潜势估算

为了解钢铁企业的大气污染特征,使用在线监测仪器于2016年7月对某典型钢铁企业VOCs（挥发性有机化合物）、PM_2.5和NMHC（非甲烷烃）等污染物进行观测,同时基于FAC（气溶胶生成系数）估算了该区域的SOA（二次有机气溶胶）生成潜势.结果表明:观测期间ρ（总VOCs）为（106.08±63.81）μg/m3,与ρ（NMHC）（以C计）的相关系数（R2）达到了0.8（P < 0.05）以上;VOCs中主要类别为烷烃和芳烃;ρ（O₃）超标期间的ρ（苯）和ρ（甲苯）分别比ρ（O₃）未超标时间段高47.0%和37.2%,并且高ρ（总VOCs）期间芳烃占比高达46.0%,这可能与钢铁企业在炼焦时苯系物（苯、甲苯和二甲苯）排放有关.ρ（总VOCs）、ρ（NMHC）、ρ（烷烃）、ρ（芳烃）和ρ（乙炔）均呈早晚高峰值的日变化特征,而ρ（烯烃）由于异戊二烯受天然源排放影响,呈午间单峰值的特征.观测期间的SOA生成潜势为2.54 μg/m3,较城区高出76.4%,显示钢铁企业SOA对PM_2.5具有一定贡献;其中芳烃对SOA生成贡献高达97.2%,主要贡献组分包括苯、间/对-二甲苯、乙苯、苯、邻-二甲苯.研究显示,钢铁企业VOCs污染治理应重点控制苯系物,同时烷烃的排放也不容忽视.      

Preparation of MnO2 decorated Co3Fe1Ox powder/monolithic catalyst with improved catalytic activity for toluene oxidation

In this paper, KMnO₄ was used to pre-treat Co₃Fe-layered double hydroxides (LDH) precursor to prepare MnO₂ decorated Co₃Fe₁O_x catalyst. The toluene oxidation performance of the catalyst was investigated systematically. The optimized 0.1MnCF-LDO catalyst exhibited the best catalytic performance, and the temperatures of 50% and 90% toluene conversion (T₅₀ and T₉₀) were 218 and 243°C, respectively. The apparent activation energy (E_a) was 31.6 kJ/mol. The characterization results showed that the pre-redox reaction by KMnO₄ could increase the specific surface area, Co³⁺ species amount and oxygen defect concentration of the catalyst, which are the main reason of the improved toluene catalytic activity. Besides, this method was also applied to enhance toluene oxidation of iron mesh based monolithic catalyst. The 0.1MnCF-LDO/Iron mesh (IM) catalyst showed a 90% toluene conversion at around 316°C which was much lower than that of without MnO₂ addition (359°C). In addition, the water resistant of all the catalysts was studied as well, all the samples showed relatively good water resistance. The toluene conversion still remained to be over >80% even in the presence of 10 vol.% water vapor.     

CO2 capture performance of bi-functional activated bleaching earth modified with basic-alcoholic solution and functionalization with monoethanolamine: isotherms, kinetics and thermodynamics

CO_2 capture performance of bifunctional activated bleaching earth(ABE) was investigated at atmospheric pressure. The sorbents were characterized by means of X-ray diffraction(XRD), Brunauer–Emmett–Teller(BET), Caron-Hydrogen-Nitrogen analysis(CHN), Fourier transform infrared(FT-IR) and thermal gravimetric analysis(TGA). The CO_2 capacity was enhanced via basic-modification and monoethanolamine(MEA) loading of the ABE sorbent to obtain a bifunctional surface property. Here, basic-modified calcined ABE with a 30 wt.%MEA loading(SAB-30) showed the highest CO_2 capture capacity, but this was decreased with excess MEA loading( 30 wt.%). At a 10%(V/V) initial CO_2 concentration feed, the maximum capacity of SAB-30 increased from 2.71 mmol/g at 30℃(without adding moisture to the feed) to 3.3 mmol/g at 50℃ when adding 10%(V/V) moisture to the feed. Increasing the moisture concentration further reduced the maximum CO_2 capacity due to the blocking effect of the excess moisture on the sorbent surface. However, SAB-30 could completely capture CO_2 even in a 100%(V/V) initial CO_2 concentration feed. A maximum CO_2 capacity of5.7 mmol/g for SAB-30 was achieved at 30℃. Varying the ratio of sorbent weight to total flow rate of the gas stream had no discernible effect on the equilibrium CO_2 capture capacity. Avrami's equation and Toth's isotherm model provided a good fitting for the data and suggested the presence of more than one reaction pathway in the CO_2 capture process and the heterogeneous adsorption surface of SAB-30. Thermodynamics studies revealed that CO_2 capture on the bifunctional SAB-30 is feasible, spontaneous and exothermic in nature.     

A chemical characterization of atmospheric aerosol in Sapporo

Monthly mean chemical composition of aerosol with diameter less than 8 μm was identified in Sapporo in 1982. The mass of aerosol was made up of nine components: elemental C, organics, SO₄²⁻, NO₃⁻, NH₄⁺, Cl⁻, Na⁺, soil particles and water. The concentrations of carbonaceous particles (elemental C and organics) was relatively high (12.7–16.0μ m⁻³) in autumn and winter (October–February) due to emission from domestic heating and comprised 36–41% of total aerosol mass. Higher concentration of soil particles was observed in spring (March–May) (9.7–13.1 μg m⁻³) and comprised 22–29% of total aerosol mass due to suspension by strong wind. On the other hand, the concentration of excess SO₄²⁻ (non-sea salt SO₄²⁻), which ranged from 2.6–5.2 μg m⁻³, did not change remarkably with season, and the fraction of excess sulfate increased to 21% in summer (July–August) probably due to photochemical transformation from SO₂. Nitrate concentration was far less than that of SO₄²⁻ throughout the year in Sapporo.     

Aerosol formation and growth in atmospheric organic/NOχ systems—I. Outdoor smog chamber studies of C7- and C8-hydrocarbons

Outdoor smog chamber experiments have been performed to determine the aerosol-forming potential of selected C₇- and C₈-hydrocarbons in sunlight-irradiated hydrocarbon-NO_χ mixtures. Measured aerosol size distributions were used to determine the rates of gas-to-particle conversion and to study the effects of the addition of SO₂ and/or NH₃ on aerosol formation and growth. The average aerosol yields by mass for the hydrocarbons studied were (the range of measured values for methylcyclohexane and 1-octene are in parentheses):

• •methylcyclohexane 9.2% (0.12–18.8);
• •1-octene 4.2% (0.17–6.9);
• •toluene 18.6%;
• •n-octane <0.001%.

The average yields are accompanied by large standard deviations (see Table 3) and depended strongly on the conditions, particularly the hydrocarbon to NO_χ initial concentration ratio. Addition of SO₂ to the organic/NO_χ systems led to an early nucleation burst and subsequent rapid growth of the newly formed aerosol. In the presence of NH₃, the gas-to-particle conversion rate of the organic/NO_χ system was enhanced perhaps due to the formation of NH₄NO₃ or the reaction of NH₃ with carboxylic acids. Sustained particle formation was observed when both SO₂ and NH₃ were present, presumably as a result of (NH₄)₂SO₄ formation. We have estimated the complexity of the 1-octene aerosol and identified 5-propyl furanone as a component of the aerosol.     

铜铈复合氧化物上石化行业典型VOCs的氧化行为与动力学

采用共沉淀法和等体积浸渍法制备了CuCeO x复合催化剂,对材料的物化性质进行了XRD、低温N2吸脱附、H2-TPR和O2-TPD表征.以石化行业典型VOCs(苯、甲苯和正己烷)为探针污染物,研究了污染物组成与浓度、反应空速、O2浓度、H2O浓度和催化剂种类对其氧化行为的影响,并对反应动力学参数进行了模型拟合.共沉淀得到的催化剂具有均匀的活性相、好的低温可还原性能和较多的活性表面氧物种.甲苯氧化率随着污染物浓度升高而降低,高转化率下苯浓度与其氧化率无相关性,正己烷的氧化率与入口浓度呈正比.苯能够显著抑制甲苯的氧化,而甲苯加入有利于苯的氧化.正己烷对苯氧化的影响较小,但能够促进甲苯的转化,苯系物对正己烷氧化有明显的抑制作用.低空速和高氧浓度都有利于污染物的氧化,氧浓度的变化对正己烷和苯的氧化影响较小.水汽对甲苯的氧化有明显的抑制作用,而对苯和正己烷氧化有明显的促进作用.共沉淀催化剂具有更好的甲苯和苯氧化性能,而无水条件下浸渍催化剂具有更好的正己烷氧化性能.拟一级动力学模型能够很好地模拟不同条件下污染物的氧化行为.     

Factors affecting airborne monocyclic aromatic hydrocarbon uptake by plants

Three factors influencing foliar uptake of monocyclic aromatic hydrocarbons (MAHs; benzene, toluene, ethylbenzene, xylenes) in situ were investigated. The first factor, the plant species, was found to determine absorption pattern and concentrations. Secondly, time variation studies showed that response of leaf concentrations to small changes in air concentrations only occurs after several days or weeks, whereas adaptation to a much higher level of air pollution takes several months. Thirdly, MAH leaf concentrations were observed to be dependent on mean air pollution at the sampling site. Bioconcentration factors BCF_vs (g m⁻³ of wet leaf/g m⁻³ of air) for MAHs in Pseudotsuga menziesii (Mirb.) Franco leaves were determined to range from 2.7 × 10⁴ to 4.7 × 10⁵.     

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process

Characteristics of toluene decomposition and formation of nitrogen oxide (NOx) by-products were investigated in a dielectric barrier discharge (DBD) reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide (MnOx), iron oxide (FeOx), cobalt oxide (CoOx) and copper oxide (CuO), supported on Al₂O₃/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO₂ selectivity. In addition, NOx was suppressed with the decrease of specific energy density (SED) and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the CuO catalyst showed the best performance in NOx suppression. The MnOx catalyst exhibited the lowest concentration of O₃ and highest CO₂ selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression.     

家具企业挥发性有机物排放特征及其环境影响

家具制造业是典型的高污染低附加值、工艺相对落后、污染治理水平低和挥发性有机物(VOCs)排放较为严重的行业,是我国VOCs防治的重点行业.本文以典型家具制造企业为研究对象,开展家具制造业VOCs排放特征和环境影响研究,获取了典型企业VOCs排放浓度水平和成分谱,分析了家具制造业VOCs的环境影响.结果表明,封边、底漆、底色、面漆和晾干等车间VOCs浓度范围为9. 18～181. 58 mg·m-3,处理设施出口VOCs浓度为30. 64～155. 94 mg·m-3,处理效率为7. 43%～67. 14%;车间主要VOCs物种为芳香烃、酯类和醛酮类物质;排气筒主要VOCs物种为酯类和芳香烃,其次为烷烃类物质;行业主要VOCs物质为乙酸仲丁酯、甲苯、间-二甲苯、甲缩醛和乙苯等.车间和排气筒VOCs平均臭氧生成潜势(OFP)分别为258. 01 mg·m-3和289. 14 mg·m-3,平均二次有机气溶胶生成潜势(SOAFP)分别为148. 66 mg·m-3和165. 31 mg·m-3,各排放环节中对OFP和SOAFP贡献最大的皆为芳香烃类物质,封边车间的OFP和SOAFP较大,应加强控制.车间边界VOCs中主要恶臭物质为乙酸仲丁酯、间-二甲苯、乙酸丁酯、对-二甲苯、乙苯、1-乙基-3-甲基苯、邻-二甲苯和甲苯,厂界VOCs几乎不产生恶臭污染.建议有针对性地加强芳香烃和酯类物质的控制.     

An intensive study on aerosol optical properties and affecting factors in Nanjing, China

The optical properties of aerosol as well as their impacting factors were investigated at a suburb site in Nanjing during autumn from 14 to 28 November 2012. More severe pollution was found together with lower visibility. The average scattering and absorption coefficients(B sca and B abs) were 375.7 ± 209.5 and 41.6 ± 18.7 Mm~(-1), respectively. Higher ?ngstr?m absorption and scattering exponents were attributed to the presence of more aged aerosol with smaller particles. Relative humidity(RH) was a key factor affecting aerosol extinction. High RH resulted in the impairment of visibility, with hygroscopic growth being independent of the dry extinction coefficient. The hygroscopic growth factor was 1.8 ± 1.2 with RH from 19% to 85%.Light absorption was enhanced by organic carbon(OC), elemental carbon(EC) and EC coatings,with contributions of 26%, 44% and 75%(532 nm), respectively. The B sca and B abs increased with increasing N_(100)(number concentration of PM_(2.5)with diameter above 100 nm), PM_1 surface concentration and PM_(2.5)mass concentration with good correlation.     

硫酸铵气溶胶对甲苯-NOx-空气体系光化学反应的影响

利用大气模拟烟雾箱,研究了硫酸铵气溶胶对甲苯-NO_x-空气体系光化学反应的影响.结果表明,硫酸铵作为气溶胶种子,其存在可以加快反应过程中颗粒物（particle matter, PM）的生成速度,并提高甲苯的气溶胶产率.在高浓度的硫酸铵气溶胶种子条件下,其初始浓度对反应过程中NO_x、NO和O₃的浓度变化没有明显的影响,但对二次有机气溶胶（secondary organic aerosol, SOA）的生成有显著影响.在硫酸铵气溶胶种子浓度小于160 μg·m^-3时,SOA的产率随初始气溶胶种子浓度的增大而增大,从最小7.2％到最大11.7％,其增幅超过60％.     

Chemical and optical properties of aerosols and their interrelationship in winter in the megacity Shanghai of China

A field campaign on air quality was carried out in Shanghai in winter of 2012. The concentrations of NO, NO₂, NO_x, SO₂, CO, and PM_2.5 increased during haze formation. The average masses of SO₄^2-, NO₃^- and NH₄⁺ were 10.3, 11.7 and 6.7 μg/m³ during the haze episodes, which exceeded the average (9.2, 7.9, and 3.4 μg/m³) of these components in the non-haze days. The mean values for the aerosol scattering coefficient (b_sp), aerosol absorption coefficient (b_ap) and single scattering albedo (SSA) were 288.7, 27.7 and 0.91 Mm^-1, respectively. A bi-peak distribution was observed for the mass concentrations of CO, NO, NO₂, and NO_x. More sulfate was produced during daytime than that in the evening due to photochemical reactions. The mass concentration of NH₄⁺ achieved a small peak at noontime. NO₃^- showed lower concentrations in the afternoon and higher concentrations in the early morning. There were obvious bi-peak diurnal patterns for bsp and bap as well as SSA. bsp and bap showed a positive correlation with PM_2.5 mass concentration. (NH₄)₂SO₄, NH₄NO₃, organic mass, elemental carbon and coarse mass accounted for 21.7%, 19.3%, 31.0%, 9.3% and 12.3% of the total extinction coefficient during non-haze days, and 25.6%, 24.3%, 30.1%, 8.1% and 8.2% during hazy days. Organic matter was the largest contributor to light extinction. The contribution proportions of ammonium sulfate and ammonium nitrate to light extinction were significantly higher during the hazy time than during the non-haze days.