Honglei Wang

Mechanism for the formation and microphysical characteristics of submicron aerosol during heavy haze pollution episode in the Yangtze River Delta, China.

In this paper we investigate a severe pollution episode that occurred in the Yangtze River Delta (YRD) region in January 2013. The episode was caused by the combination of anthropogenic emissions and unusual atmospheric circulation, the depression of strong cold air activities and the very unfavorable dispersion. The episode contained three haze events (haze1: Jan. 4-9, haze2: Jan. 10-13, and haze3: Jan. 14-16). In Nanjing, aerosol size distributions from 10nm to 10 μm and chemical components of single particles from 0.2 to 2 μm were measured with a Wide Range Particle Spectrometer (WPS) and a Single Particle Aerosol Mass Spectrometer (SPAMS), respectively. The results indicate that the mean PM2.5 concentrations in the YRD region were greater than 110 μg·m(-3). The highest PM2.5 concentration of 175.6 μg·m(-3) occurred in Nanjing; the other cities had values in the range of 110.8-147.3 μg·m(-3). The average PM2.5 concentrations were 58.3, 122.7, 145.4 and 154.7 μg·m(-3) on clean and haze1, haze2 and haze3 days, respectively. The highest PM2.5 values of 416.5, 415.5 and 300.5 μg·m(-3) in Nanjing occurred during the three haze events. The spectra of the aerosol number concentrations had unimodal distributions on clean and haze days. The maximum surface area peaks were located at 0.5-0.7 μm and had values of 419, 1397, 1309 and 1378 μm(2)·cm(-3)·nm(-1) on clean and haze1, haze2 and haze3 days, respectively. The number concentrations of biomass/biofuel burning-containing particles (biomass), organic carbon-containing particles (OC), elemental carbon-containing particles (EC), nitrate-containing particles (nitrate) and sulfate-containing particles (sulfate) increased significantly during the haze events. The chemical components of the aerosols during the haze1 and haze2 events were similar to those on clean days, and variations were caused by local particle accumulations under poor diffusion conditions. The high EC particle concentration of 24.76% during the haze3 event was impacted by the pollutants transported from surrounding cities. In addition, the different chemical components showed distinct size distributions.

One year online measurements of water-soluble ions at the industrially polluted town of Nanjing, China: Sources, seasonal and diurnal variations

Half-hourly mass concentrations water-soluble ions (WSIs) and PM2.5 were measured online a Rapid Collector of Fine Particles and Ion Chromatography system (RCFP-IC) and FH62C14 Continuous Particulate Monitor in Nanjing from October 18, 2013 to November 17, 2014. The WSIs concentration ranged from 7.07 to 333.42 μg m(-3) with an annual mean of 76.32 μg m(-3). The WSIs ranked in the order of SO4(2-) > NH4(+) > NO3(-) > Cl(-) > NO2(-) > K(+) > Ca(2+) > Na(+) > Mg(2+). The PM2.5 concentration ranged from 4.00 to 400 μg m(-3) with an annual mean of 83.58 μg m(-3). The concentrations of WSIs varied in the order of winter (115.77 μg m(-3)) > spring (76.10 μg m(-3)) > autumn (63.72 μg m(-3)) > summer (59.75 μg m(-3)), with the highest level in January (123.99 μg m(-3)) and lowest level in August (43.73 μg m(-3)). Different WSIs had distinct diurnal variations. The source analysis of the WSIs in the PCA/APCS mode illustrated that the sources consisted of secondary aerosol, coal combustion, mineral dust, biomass burning, traffic emissions and sea salt. In addition, there were seasonal variations amongst the various sources. The haze formation mechanism was different in summer and winter. The winter was dominated by NH4NO3 (18.56%), (NH4)2SO4 (28.63%), NH4(+) (11.27%), SO4(2-) (18.35%) and NO3(-) (13.13%), and by NH3 (25.93%), (NH4)2SO4 (13.37%), SO4(2-) (15.74%) and NO3(-) (9.97%) in summer. Consequently, the proportions of HCl, HNO3, NH4(+), SO4(2-) and NO3(-) were much larger during haze episodes in winter, while it was dominated by NH4NO3, NH4(+), (NH4)2SO4, SO4(2-) and NO3(-) during summer haze episodes.

Size distributions of aerosol and water-soluble ions in Nanjing during a crop residual burning event.

To investigate the impact on urban air pollution by crop residual burning outside Nanjing, aerosol concentration, pollution gas concentration, mass concentration, and water-soluble ion size distribution were observed during one event of November 4-9, 2010. Results show that the size distribution of aerosol concentration is bimodal on pollution days and normal days, with peak values at 60-70 and 200-300 nm, respectively. Aerosol concentration is 10(4) cm(-3) x nm(-1) on pollution days. The peak value of spectrum distribution of aerosol concentration on pollution days is 1.5-3.3 times higher than that on a normal day. Crop residual burning has a great impact on the concentration of fine particles. Diurnal variation of aerosol concentration is trimodal on pollution days and normal days, with peak values at 03:00, 09:00 and 19:00 local standard time. The first peak is impacted by meteorological elements, while the second and third peaks are due to human activities, such as rush hour traffic. Crop residual burning has the greatest impact on SO2 concentration, followed by NO2, O3 is hardly affected. The impact of crop residual burning on fine particles (< 2.1 microm) is larger than on coarse particles (> 2.1 microm), thus ion concentration in fine particles is higher than that in coarse particles. Crop residual burning leads to similar increase in all ion components, thus it has a small impact on the water-soluble ions order. Crop residual burning has a strong impact on the size distribution of K+, Cl-, Na+, and F- and has a weak impact on the size distributions of NH4+, Ca2+, NO3- and SO4(2-).

Characteristics of the water-soluble components of aerosol particles in Hefei, China

Size-classified daily aerosol mass concentrations and concentrations of water-soluble inorganic ions were measured in Hefei, China, in four representative months between September 2012 and August 2013. An annual average mass concentration of 169.09 μg/m(3) for total suspended particulate (TSP) was measured using an Andersen Mark-II cascade impactor. The seasonal average mass concentration was highest in winter (234.73 μg/m(3)) and lowest in summer (91.71 μg/m(3)). Water-soluble ions accounted for 59.49%, 32.90%, 48.62% and 37.08% of the aerosol mass concentration in winter, spring, summer, and fall, respectively, which indicated that ionic species were the primary constituents of the atmospheric aerosols. The four most abundant ions were NO3(-), SO4(2-), Ca(2+) and NH4(+). With the exception of Ca(2+), the mass concentrations of water-soluble ions were in an intermediate range compared with the levels for other Chinese cities. Sulfate, nitrate, and ammonium were the dominant fine-particle species, which were bimodally distributed in spring, summer and fall; however, the size distribution became unimodal in winter, with a peak at 1.1-2.1 μm. The Ca(2+) peak occurred at approximately 4.7-5.8 μm in all seasons. The cation to anion ratio was close to 1.4, which suggested that the aerosol particles were alkalescent in Hefei. The average NO3(-)/SO4(2-) mass ratio was 1.10 in Hefei, which indicated that mobile source emissions were predominant. Significant positive correlation coefficients between the concentrations of NH4(+) and SO4(2-), NH4(+) and NO3(-), SO4(2-) and NO3(-), and Mg(2+) and Ca(2+) were also indicated, suggesting that aerosol particles may be present as (NH4)2SO4, NH4HSO4, and NH4NO3.

Observation of aerosol size distribution and new particle formation at a coastal city in the Yangtze River Delta, China.

Aerosol number size distribution in the range of 10nm-10μm, trace gases (O3, CO, SO2 and NO2), particular matter (PM: PM2.5 and PM10) and meteorological elements were measured from the 1st to the 31st of May, 2015, in the coastal city of Jiaxing in the Yangtze River Delta (YRD). The average number concentration and surface area concentration were 19,639cm(-3) and 427μm(2)cm(-3) during the observation period. The different mode particle concentrations ranked in the order of Aitken mode (12,361cm(-3))>nucleation (4926.7cm(-3))>accumulation (2349.3cm(-3))>coarse mode (1.7cm(-3)). The average concentrations of CO, SO2, NO2, O3, PM2.5 and PM10 were 0.545mgm(-3), 14.7, 35.1, 89.8, 43.5 and 64.6μgm(-3), respectively. Eight precipitation processes and 15 new particle formation (NPF) events (3 NPF events occurred on a rainy day) were observed. Results show that the precipitation process had greater scavenging effects on particles smaller than 120nm and larger than 2μm. The spectral distributions of number concentrations were unimodal at different weather conditions, with peaks at 20nm, 40-60nm, 50-80nm on NPF days, rainy days and normal days. During the NPF events, the formation rate (FR), growth rate (GR), condensational sink (CS), vapor source rate (Q) and condensing vapor concentration (C) were in the range of 4.0-17.0cm(-3)s(-1), 2.2-15.7nmh(-1), 1.5-5.8×10(-2)s(-1), 0.5-7.7×10(6)cm(-3)s(-1) and 3.0-21.5×10(7)cm(-3), with mean values of 9.6cm(-3)s(-1), 6.8nmh(-1), 3.4×10(-2)s(-1), 3.3×10(6)cm(-3)s(-1) and 9.4×10(7)cm(-3), respectively. NPF events normally occurred under clean atmospheric conditions with low PM concentrations but high levels of trace gases. It was also found that SO2 plays an important role in NPF and growth in Jiaxing.

Study on the aerosol characteristics in the different urban functional zones

It has become clear that aerosols play a more important role in most urban air pollution problems. The aerosol characteristics in the different urban functional zones of Nanjing has been observed and analyzed in autumn of 2009. The aerosol number concentration in each urban functional zone showed a close similarity and reached pretty high value, 104cm−3. The number concentration and surface area concentration of spectrum distribution in study period showed two and three peaks, respectively. The particle scavenging efficiency was compared among rainfall, snowfall, and fog. The results showed that the effect of precipitation on the local aerosols dominated a major factor in clear, and fog impact on the diurnal variation of the aerosol number concentration significantly. The seasonal variations of aerosol were also discussed. The mass concentration varied significantly, autumn> summer, while the fine particle quality percentage in autumn was higher than that in summer.

PM 10 , PM 2.1 and associated water-soluble inorganic ions at urban and suburban sites in Nanjing, China

Airborne particles, especially particle size smaller than 10µm, samples were collected at two sites in Nanjing from October 2009 to August 2010. The mass concentrations of ten water-soluble ions (NO<inf>2</inf>⁻, F⁻, NO<inf>3</inf>⁻, Cl⁻, SO<inf>4</inf>²⁺, NH<inf>4</inf>⁺, Mg²⁺, Ca²⁺, Na⁺, K⁺) were measured for all the samples. At suburban site, the seasonal variation of PM<inf>10</inf> was spring>fall>winter>summer, while PM<inf>2.1</inf> was winter>fall>spring>summer. The mass concentration of PM<inf>10</inf> was highest in spring; however, the ratio of PM<inf>2.1</inf>/PM<inf>10</inf> was the lowest. In summer, PM<inf>2.1</inf> pollution can not be ignored. Compared with urban site, the concentration of particles was higher at suburban site, which likely due to be under the influence of industrial zone. In summer, SO<inf>4</inf>²⁻, NO<inf>3</inf>⁻, and NH<inf>4</inf>⁺, secondary formed compounds, were major ions, totally accounting for 29.51% and 47.45% at urban site, 37.63% and 49.04% at suburban site in PM<inf>10</inf> and PM<inf>2.1</inf>, respectively. The ratios of NO<inf>3</inf>⁻/SO<inf>4</inf>²⁻ were smaller than 1 suggesting that stationary source emissions were more important than the vehicle emissions in summer. NO<inf>3</inf><inf>−</inf>, SO<inf>4</inf>²⁻ and NH<inf>4</inf>⁺ showed good correlations between each other both in PM<inf>10</inf> and PM<inf>2.1</inf>, and they were in form of NH<inf>4</inf>NO<inf>3</inf> and (NH<inf>4</inf>)<inf>2</inf>SO<inf>4</inf> in particles. As a tracer ion of biomass burning, the mass concentration of K⁺ was not ignored in Nanjing, which is much higher in suburban area. Furthermore, K⁺ had good correlations with other ions, indicating that burning activities of crop aggravated the air quality.