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Studying the evolution of secondary inorganic aerosols, which are important components of PM 2.5 , is crucial to improving our understanding about the air pollution in big cities. This study investigates the evolution and factors of secondary inorganic aerosols based on two pollution incidences in Nanjing in June 2014. A significant characteristic of air pollution complex with the coexistence of higher concentrations of both PM 2.5 and ozone is observed. In the earlier stage of the pollution episode, ozone concentrations were high, which could exceed 250, triggering a stronger oxidation in the atmosphere and a higher production potential of nitric acid that leads to the quick production of nitrate. In the later period of the pollution episode, relative humidity played an essential role. An increase in relative humidity would result in a sharp decrease in the theoretical product of the partial pressures of NH 3 and HNO 3 , especially when relative humidity exceeds the mutual deliquesce relative humidity that makes it easier to form nitrate. The difference in the theoretical and observational partial pressure product could characterize the evolution of nitrate perfectly.

In December 2013,a lasting haze pollution event occurred in the Central and East regions of China.Here in this paper,using a single-particle soot photometer (SP2),we studied mass concentrations,mixing states,and size distributions of black carbon (BC) in this event.The results showed that BC mass concentration in Nanjing during the observation period was in the range of 1.01-14.05 μg·m -3 with an average of 4.39 μg·m -3 ,showing the characteristics of double peaks for lighter pollution,andhigh in the nighttime and low in the daytime during heavier pollution.Using the relative coating thickness ( D p / D c ) to define mixing state of black carbon,diurnal variations were higher in early morning and noon when slightly polluted,and lower during rush hour,indicating the degree of BC ageing was deeper in the morning and afternoon,with fresher particles near the ground source emissions during rush hour.The relative coating thickness did not vary greatly throughout the day when heavily polluted,which was expected to be linked to regional pollutants and it also showed Gas-solid transformation under high relative humidity.The average mass and number size distribution had single peaking with the same BC volume-equivalent diameter in different degrees of pollution,with the peak diameter at 100 nm for the number distribution when heavily polluted,at 91 nm when slightly polluted,and at 210 nm for the mass distribution regardless of the degree of pollution.We could find regional differences of BC sources by comparing the observed research worldwide.This study has very important reference value for the in-depth understanding of BC pollution in Yangtze River Delta.

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 PM 10 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 PM 1.1 , PM 2.1 and PM 10 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%.

Volatile organic compounds (VOCs) is an important precursor of photochemical ozone pollution (O3) in the atmosphere. Their concentration variation directly affects the characteristics of the ozone pollution. The concentration, speciation of VOCs, ozone and its precursors in Nanjing were analyzed and measured using online gas detection systems in August 2013. VOCs/NOx discriminant method was used to get the sensitive control factors of ozone. The results showed that the averaged volume fraction of VOCs was 52. 05 x 10(-9), and the largest one reached 200 x 10(-9) in Nanjing urban district. The order of volume fraction of each species VOCs was alkane > oxygen-containing VOCs > alkene > aromatics. The averaged concentration of ozone was 76.5 microg x m(-1) and the exceeding concentration of hourly standard was 5.9%. The change trends of ozone precursors VOCs and NOx were basically identical and Ozone showed the obvious negative correlation during the period of high concentrations of ozone. There were some differences in the concentrations of the same VOCs in different ozone concentration periods. The ozone generation in Nanjing urban district was sensitive to VOCs, and Nanjing belonged to VOCs control area in summer.

Emission inventory of air pollutants is the key to understand the spatial and temporal distribution of atmospheric pollutants and to accurately simulate the ambient air quality. The currently established emission inventories are still limited on spatial and temporal resolution which greatly influences the numerical prediction accuracy of air quality. With coal-fired stationary sources considered, this study analyzed the total emissions and monthly variation of main pollutants from them in 2012 as the basic year, by collecting the on-line monitoring data for power plants and atmospheric verifiable accounting tables of Jiangsu Province. Emission factors in documents are summarized and adopted. Results indicated that the emission amounts of SO2, NOx, TSP, PM10, PM2.5, CO, EC, OC, NMVOC and NH3 were 106.0, 278.3, 40.9, 32.7, 21.7, 582.0, 3.6, 2.5, 17.3 and 2.2 kt, respectively. They presented monthly variation with high emission amounts in February, March, July, August and December and low emissions in September and October. The reason may be that more coal are consumed which leads to the increase of pollutants emitted, to satisfy the needs, of heat and electricity power supply in cold and hot periods. Local emission factors are needed for emission inventory studies and the monthly variation should be considered when emission inventories are used in air quality simulation.

A continuous observation campaign was carried out with the GC5000 volatile organics online monitoring system and the EMS system for one month in November 2011 in the northern suburb of Nanjing, and 56 VOC components and reactive gases (NO(x), CO and O3) were measured. The results showed that the VOC hourly averaged volume fraction in Nanjing northern suburb was about 48.17 x 10(-9), and the minimum value of VOCs occurred at 16:00. The diurnal variation showed a bimodal characteristic, indicating the significant impact of motor vehicle emission. The VOC concentration and O3 concentration exhibited negative correlation in the daytime. The average OH consumption rate of VOCs was approximately 3.26 x 10(-12) cm3 x (molecule x s)(-1), and the largest incremental reactivity was about 3.26 mol x mol(-1); Alkenes contributed the largest-parts of the OH consumption rate (L(OH)) and the ozone formation potential (OFP), followed by aromatics. Although alkanes were the most abundant components of VOCs in the atmosphere, it is not the main contributor of L(OH) and OFP. The key active components in VOCs were ethylene, propylene, 1-butene, m,p-xylene and isoprene, etc. The dominant factor of ozone formation was VOCs in this observation.

Based on meteorological data and aerosol samples from Nov.15 to Dec.30,2007 in the north suburb of Nanjing, size distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) in PM10 in foggy and sunny days were studied, and the concentrations of 16 PAHs were analyzed by gas chromatography with mass selective detection (GC-MS). The average concentrations of aerosols in the night (PM2.1 : 120.34 microg x m(-3; PM10 : 215.92 microg*m(-3) are close to those in the daytime (PM2.1 : 26.76 microg.m(-3); PM9.0 : 213.41 microg x m(-3)) in foggy days. The average concentrations of aerosols are higher in the night (PM2.1 : 71.45 microg x m(-3); PM9.0 : 114.33 microg x m(-3)) than those in the daytime (PM2.1 : 41.02 microg x m(-3); PM9.0 : 74.38 microg x m(-3)) in fine days. And we also find that the total concentrations of 16 PAHs in PM2.1 (49.97 ng x m(-3)) and PM9.0 (59.45 ng x m(-3)) in foggy days are 1.50 and 1.46 times of those (PM2.1 : 33.30 ng x m(-3); PM9.0 : 40.80 ng x m(-3)) in fine days separately. The average maximum concentrations of individual PAHs are fluoranthene, which are higher (PM2.1 : 7.98 ng x m(-3); PM9.0 : 9.99 ng x m(-3)) in foggy days than those (PM2.5 : 5.23 ng x m(-3); PM9.0 : 6.77 ng x m(-3)) in fine days, and the average concentrations of benzo-apyrene are higher in fog days (PM2.1 : 1.77 ng x m(-3); PM9.0 : 1.99 ng x m(-3)) than those in fine days (PM2.1 : 1.46 microg x m(-3); PM9.0 : 1.84 ng x m(-3)).Those results indicate that the fog processing could aggravate the pollution of PM2.5 and PM10 near the ground layer. Diurnal size distribution of total PAHs in PM10 is consistent with that of PM10 in foggy and sunny days, and size distribution investigated was bi-modal with a peak in accumulation particle mode and another peak in coarse particle mode aerosol. Size distributions of PM10 and total PAHs in PM10 are affected greatly by the day fog in daytime, while those are affected little by the night fog in night.