[Secondary Organic Aerosol Mass Yield and Characteristics from 4-ethylguaiacol Aqueous·OH Oxidation: Effects of Initial Concentration].

Aqueous-phase chemical processing, as an essential formation pathway of secondary organic aerosol (SOA), has attracted widespread attention from within atmospheric chemistry fields. Due to the complicated reaction nature, reaction mechanisms, and product characteristics of aqueous-phase chemical processing, its contribution to the SOA budget is still not fully understood. In this work, we investigate how the initial concentration (0.03-3 mmol·L-1) of 4-ethylguaiacol affects SOA formation of aqueous·OH photochemical oxidation. We use soot-particle aerosol mass spectrometry (SP-AMS) to monitor SOA mass yield and oxidation character, and gas chromatography-mass spectrometry (GC-MS) and ion chromatography (IC) to measure products and organic acids. Additionally, we use ultraviolet visible spectroscopy (UV-vis) and high-performance liquid spectrometry (HPLS) to track the formation of light-absorbing products such as humic-like substances (HULIS). Our research indicated that the range of the O/C ratio of EG-aqSOA measured by the SP-AMS exhibited increasing trends with increased reaction time 0.42-0.61 (0.03 mmol·L-1), 0.49-0.84 (0.3 mmol·L-1), and 0.49-0.63 (3 mmol·L-1). Dimers (C16H18 O2+, m/z 302) via SP-AMS were obviously higher under a higher initial concentration, thereby demonstrating that the oligomerization reaction proceeded more easily. The absorption at 250 nm recorded by UV-vis was distinctly enhanced, which might be attributed to new light-absorbing products with absorbance at 250 nm. Furthermore, the HULIS concentration increased with reaction time, in accordance with enhancement of absorbance in the 300-400 nm region, thus suggesting that aqueous-phase processing formed brown carbon. Small organic acids, including formic acid, malic acid, and oxalic acid, were detected by IC in all reaction solutions, with the highest concentration being for formic acid. GC/MS detected ketone, an OH monomer, and dimers in the aqSOA, which further indicates that functionalization and oligomerization took place.

[Secondary Organic Aerosols from Aqueous Reaction of Aerosol Water].

Liquid water (cloud/fog droplets and aerosols) is ubiquitous in the atmosphere and can provide an important reaction media for aqueous-phase chemical reactions. Gaseous precursors (mainly VOCs) or their gas-phase initial or first-generation oxidation products (including intermediate-volatility and semi-volatile organic compounds; I/SVOCs) can undergo chemical reactions in the atmospheric condensed phase (aqueous phase) to form low-volatility, highly oxidized organic matter[e.g., some key tracer species such as organosulfates (OSs) and organonitrogens (ONs)]. These products largely remain in the particle phase upon water evaporation and are referred to as aqueous secondary organic aerosols (aqSOAs). aqSOAs have been emerging as a research hot topic in atmospheric chemistry, as they can contribute significantly to OAs and thus have important impacts on the environment, climate, and human health. Despite considerable progress, so far, aqSOAs remain poorly understood owing to their complex formation mechanisms. In this review, we focus mainly on the relevant research results on the SOAs formed in aerosol water-aqueous aerosol SOAs (aaSOAs)-including gas-phase precursors, formation mechanisms, laboratory simulations, and field observations, as well as SOA yield and contribution to OAs. Meanwhile, we propose future directions regarding studies of sources and formation mechanisms of aaSOAs, including identification of unknown aaSOA precursors and tracer products, photosensitizer-triggered radical chemistry, formation pathways of OS and ON compounds, field observations and model simulations of aaSOAs.

[Pollution Characteristics and Light Extinction Contribution of Water-soluble Ions of PM2.5 in Hangzhou].

The pollution characteristics and light extinction contribution of water-soluble ions of PM2.5 in Hangzhou were investigated by sampling and laboratory analysis of aerosol samplers in 2013. The water-soluble ions were dominant in PM2.5 and the total mass concentration was 37.5 µg·m-3, accounting for 44.4% of the PM2.5 mass concentration. Water-soluble ions were mainly composed of secondary ions(SO42-,NO3- and NH4+), which accounted for 83.4% of total ions. The highest mass concentrations of PM2.5 and major ions were observed in winter and the lowest in summer. The proportions of water-soluble ions in PM2.5 in summer and autumn were obviously higher than those in winter and spring and proportions of secondary ions in water-soluble ions were very close in each season. The contribution was the greatest to PM2.5 from secondary ions generation caused by fuel combustion and automobile exhaust. The annual average values of SOR and NOR were 0.27 and 0.15 respectively, the conversion rate of SO2 in atmosphere was greater than that of NOx. There was obvious positive correlation between SOR or NOR and humidity which indicated the important contribution of heterogeneous oxidation process to the generation of SO42- and NO3-. The annual average of[NO3-]/[SO42-] was 0.63, and the aerosol pollution was primarily affected by emissions from coal burning. In haze days, with the increase of haze pollution level, the mass concentrations of PM2.5, water-soluble ions, secondary ions as well as SOR and NOR all increased gradually, and the stable weather condition in haze days could efficiently promote the accumulation and secondary conversion of pollutants. There were obvious positive correlations between mass concentrations of PM2.5 and SNA and the atmospheric light extinction coefficient. The IMPROVE formula which was used to calculate the light extinction coefficients of different chemical components could efficiently indicate the tendency of aerosol scattering. The extinction contribution of SNA could reach 60.8%. The extinction coefficient of SNA was the highest in winter and lowest in summer, and its value and contribution proportion both increased gradually as the haze pollution level rose.

[Pollution Characteristics and Source Identification of PAHs in Atmospheric PM2.5 in Changzhou City].

A total of 55 ambient fine particle (PM2.5) samples were collected in Changzhou City from January to August 2016. The concentrations of 17 PM2.5-bound PAHs in the samples were analyzed by GC-MS. Results showed that seasonal average mass concentrations of PAHs in winter, spring, and summer were 140.24, 41.42, and 2.96 ng·m-3, respectively, which indicating that the pollution of PAHs in winter appeared more serious than in the other two seasons, and 4-6-ring high molecular weight PAHs were predominant in all three seasons. The average daily level of BaP was 3.64 ng·m-3 and the days it exceeded the permitted standard accounted for 41% of total days. PAH concentration had significant negative correlations with temperature (correlation coefficient: -0.643) and visibility (correlation coefficient: -0.466), whereas it had good positive correlations with atmospheric pressure (correlation coefficient: 0.544) and poor correlations with wind speed and relative humidity. PAH concentrations were higher at nighttime than at daytime, because of the influences of temperature difference, atmospheric stratification, as well as pollution sources. The results from the air backward trajectory model indicated that PM2.5-bound PAHs in Changzhou were mainly affected by local emission sources and short-distance transportation, whereas the contribution of long-distance transmission was small (only 11%). Based on analysis of characteristic ratios, PAHs were mainly sourced from coal burning, vehicle emissions, and biomass burning. An incremental lifetime cancer risk (ILCR) model was used to evaluate the health impact of PAHs via breathing exposure pathways. Results revealed that the ILCR of adults was higher than that of children. The ILCRs of the group for winter and spring were slightly higher than the risk threshold, but a difference was not obvious for summer.

[Pollution Characteristics of Aerosol Number Concentration in Winter and Spring in a Northern Suburb of Nanjing].

Using APS-3321, the atmospheric aerosol number concentrations (0.5-20 µm) were continuously monitored to analyze the characteristics of winter and spring pollution in 2014 in a northern suburb of Nanjing. The average number concentrations were (364.8±297.8) cm-3 and (79.6±62.4) cm-3 in winter and spring, respectively; fine particles (0.5-1.0 µm) accounted for 87.8% and 86.6% of the total, respectively. There were significant variations in number concentration at different periods. The diurnal variations in number concentrations were evident with high concentrations at night and low concentrations during the day. The early peaks were at 07:00 and 09:00, and number concentrations began to increase rapidly starting at 17:00 and 18:00 in winter and spring, respectively. The distribution of the number concentrations was unimodal, with peak sizes between 0.583 and 0.626 µm in winter and less than 0.542 µm in spring. With the increase in relative humidity, aerosol number concentrations increased gradually; at the same time, the peak size moved to a larger diameter which reflected the influence of hygroscopic growth of aerosols. During the total observation period, it reached 83.3% of the proportion of hazy days. The number concentration of particles less than 2.0 µm increased significantly with the increase in the haze pollution level, which was more obvious in winter. In spring, the proportion of fine particles increased with the increase in the haze level but in winter, it decreased during hazy days due to a significant increase in particle size caused by aging. The analysis of the typical pollution process in January indicated that there was a strong correlation between the source of air mass and the surface wind direction. Pollutants transmitted from the northern Jiangsu Province and the accumulation of pollutants due to slow winds were important causations of the pollution process.

[Variation of Size Distribution and the Influencing Factors of Aerosol in Northern Suburbs of Nanjing].

The size distribution of particulate was analyzed by the FA-3 9 stage sampler in Northern-suburb of Nanjing from January to November in 2014. First, the monitoring result from FA-3 was compared with the results of the same period obtained from a medium flow size grading sampler (KC-120H) and online monitoring instrument of the Environmental Protection Agency. The data correlation coefficients were all greater than 0.95. The fine particle concentration from FA-3 was lower by 13.9% and 16.6%, while PM10 concentration was higher by 15.2% and 13.3% respectively. However, the deviations were in the acceptable range of atmospheric sampling which could indicate the accurate classification and sampling of particulate for FA-3. Particulate pollution in Northern-suburb Nanjing was serous in which the annual average concentrations of PM1.1, PM2.1 and PM10 were(65.6±37.6), (91.0±54.7) and (168.0±87.0) µg·m-3 respectively; fine particles dominated and most of them had a diameter of less than 1.1 µm. Particle size distribution was bimodal with peaks at 0.43-0.65 and 9-10 µm; the median diameter was 1.83 µm which was in the accumulation mode. In winter, the concentration of fine particle size was higher and in spring the coarse particle size was higher; in summer, the fine particle size concentration was not significantly reduced but coarse particle size was obviously lower than those in other seasons. The differences of particle size distribution in day and at night were very small in coarse segment and in fine segment, the nocturnal concentrations were mostly higher than diurnal concentrations. The precipitation had cleaning effect for each size range of particulate except in summer and the effect was more distinct in fine particle size. In haze days, with the aggravation of haze level, the particle concentration in the diameter range of 0.43-2.1 µm increased gradually while in this segment the particle concentration was significantly negatively correlated with visibility. Using relative humidity of 70% as the demarcation, the particle size distribution changed significantly:when humidity was greater than 70%, mass concentration of particle with a diameter of less than 0.43 µm reduced significantly but that with diameter range of 0.43-2.1 µm increased obviously which should be related to the particle hygroscopic growth. The air mass sources could be divided into four categories in northern-suburb of Nanjing. Air mass from the northwest with rapid transport velocity was the cleanest in which the fine particle size concentration was significantly lower than those in other directions; the air mass from local and surrounding was the most severely polluted with high concentrations in both fine and coarse segment, its transmission distance was short and wind speed was small which contributed greatly to air pollution of Nanjing with probability of occurrence of pollution reaching 73.9%.