Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. Sulfate is a major component of fine haze particles. Record sulfate concentrations of up to ~300 μg m −3 were observed during the January 2013 winter haze event in Beijing. State-of-the-art air quality models that rely on sulfate production mechanisms requiring photochemical oxidants cannot predict these high levels because of the weak photochemistry activity during haze events. We find that the missing source of sulfate and particulate matter can be explained by reactive nitrogen chemistry in aerosol water. The aerosol water serves as a reactor, where the alkaline aerosol components trap SO 2 , which is oxidized by NO 2 to form sulfate, whereby high reaction rates are sustained by the high neutralizing capacity of the atmosphere in northern China. This mechanism is self-amplifying because higher aerosol mass concentration corresponds to higher aerosol water content, leading to faster sulfate production and more severe haze pollution.

Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China

. Extreme haze episodes repeatedly shrouded Beijing during the winter of 2012–2013, causing major environmental and health problems. To better understand these extreme events, we performed a model-assisted analysis of the hourly observation data of PM2.5 and its major chemical compositions. The synthetic analysis shows that (1) the severe winter haze was driven by stable synoptic meteorological conditions over northeastern China, and not by an abrupt increase in anthropogenic emissions. (2) Secondary species, including organics, sulfate, nitrate, and ammonium, were the major constituents of PM2.5 during this period. (3) Due to the dimming effect of high loading of aerosol particles, gaseous oxidant concentrations decreased significantly, suggesting a reduced production of secondary aerosols through gas-phase reactions. Surprisingly, the observational data reveals an enhanced production rate of secondary aerosols, suggesting an important contribution from other formation pathways, most likely heterogeneous reactions. These reactions appeared to be more efficient in producing secondary inorganics aerosols than organic aerosols resulting in a strongly elevated fraction of inorganics during heavily polluted periods. (4) Moreover, we found that high aerosol concentration was a regional phenomenon. The accumulation process of aerosol particles occurred successively from cities southeast of Beijing. The apparent sharp increase in PM2.5 concentration of up to several hundred μg m−3 per hour recorded in Beijing represented rapid recovery from an interruption to the continuous pollution accumulation over the region, rather than purely local chemical production. This suggests that regional transport of pollutants played an important role during these severe pollution events.

/pdf/exploring-the-severe-winter-haze-in-beijing-the-impact-of-xph7x56h03.pdf

Exploring the severe winter haze in Beijing: the impact of synoptic weather, regional transport and heterogeneous reactions

This study presents one of the first long term datasets including a statistical summary of PM2.5 concentrations obtained from one-year monitoring in 190 cities in China. We found only 25 out of 190 cities could meet the National Ambient Air Quality Standards of China, and the population-weighted mean of PM2.5 in Chinese cities are 61 μg/m3, ~3 times as high as global population-weighted mean, highlighting a high health risk. PM2.5 concentrations are generally higher in north than in south regions due to relative large PM emissions and unfavorable meteorological conditions for pollution dispersion. A remarkable seasonal variability of PM2.5 is observed with the highest during the winter and the lowest during the summer. Due to the enhanced contributions from dust particles and open biomass burning, high PM2.5 abundances are also found in the spring (in Northwest and West Central China) and autumn (in East China), respectively. In addition, we found the lowest and highest PM2.5 often occurs in the afternoon and evening hours, respectively, associated with daily variation of the boundary layer depth and anthropogenic emissions. The diurnal distribution of the PM2.5-to-CO ratio consistently displays a pronounced peak during the afternoon periods, reflecting a significant contribution of secondary PM formation.

/pdf/fine-particulate-matter-pm-2-5-in-china-at-a-city-level-3iffqhow56.pdf

Fine particulate matter (PM 2.5) in China at a city level

Biomass is an important primary energy source as well as renewable energy source. As the most promising biomass utilization method, gasification/pyrolysis produces not only useful fuel gases, char and chemicals, but also some byproducts like fly ash, NOx, SO2 and tar. Tar in the product gases will condense at low temperature, and lead to clogged or blockage in fuel lines, filters and engines. Moreover, too much tar in product gases will reduce the utilization efficiency of biomass. Therefore, the reduction or decomposition of tar in biomass derived fuel gases is one of the biggest obstacles in its utilization for power generation. In this paper, we review the literatures pertaining to tar reduction or destruction methods during biomass gasification/pyrolysis. On the basis of their characteristics, the current tar reduction or destruction methods can be broadly divided into five main groups: mechanism methods, self-modification, thermal cracking, catalyst cracking and plasma methods.

The reduction and control technology of tar during biomass gasification/pyrolysis: An overview

Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies Pascal Granger* and Vasile I. Parvulescu* Unit e de Catalyse et de Chimie du Solide, UMR CNRS 8181, University of Lille 1, 59655 Villeneuve d’Ascq, France Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, Romania, 412 Regina Elisabeta Boulevard, Bucharest 030016, Romania

Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies

. In January 2013, Beijing experienced several serious haze events. To achieve a better understanding of the characteristics, sources and processes of aerosols during this month, an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed at an urban site between 1 January and 1 February 2013 to obtain the size-resolved chemical composition of non-refractory submicron particles (NR-PM1). During this period, the mean measured NR-PM1 mass concentration was 89.3 ± 85.6 μg m−3, and it peaked at 423 μg m−3. Positive matrix factorization (PMF) differentiated the organic aerosol into five components, including a highly oxidized, low-volatility oxygenated organic aerosol (LV-OOA), a less oxidized, semi-volatile oxygenated OA (SV-OOA), a coal combustion OA (CCOA), a cooking-related OA (COA), and a hydrocarbon-like OA (HOA), which on average accounted for 28%, 26%, 15%, 20% and 11% of the total organic mass, respectively. A detailed comparison between the polluted days and unpolluted days found many interesting results. First, the organic fraction was the most important NR-PM1 species during the unpolluted days (58%), while inorganic species were dominant on polluted days (59%). The OA composition also experienced a significant change; it was dominated by primary OA (POA), including COA, HOA and CCOA, on unpolluted days. The contribution of secondary OA (SOA) increased from 35% to 63% between unpolluted and polluted days. Second, meteorological effects played an important role in the heavy pollution in this month and differed significantly between the two types of days. The temperature and relative humidity (RH) were all increased on polluted days and the wind speed and air pressure were decreased. Third, the diurnal variation trend in NR-PM1 species and OA components showed some differences between the two types of days, and the OA was more highly oxidized on polluted days. Fourth, the effects of air masses were significantly different between the two types of days; air was mainly transported from contaminated areas on the polluted days. The comparison also found that the aerosol was more acidic on polluted days. Additionally, the variation trends of the mass concentration and mass fractions of NR-PM1 species and OA components were more dramatic when the NR-PM1 mass loading was at a higher level. The serious pollution observed in this month can be attributed to the synergy of unfavorable meteorological factors, the transport of air masses from high-pollution areas, emission by local sources, and other factors.

/pdf/characterization-of-submicron-aerosols-during-a-month-of-2u2vjmfxwe.pdf

Characterization of submicron aerosols during a month of serious pollution in Beijing, 2013

Formation and reaction of ammonium sulfate salts on V2O5/AC catalyst during selective catalytic reduction of nitric oxide by ammonia at low temperatures

Simultaneous removal of SO2 and NOx from flue gas using a CuO/Al2O3 catalyst sorbent: I. Deactivation of SCR activity by SO2 at low temperatures

The inhibition effect of H2O on V2O5/AC catalyst for NO reduction with NH3 is studied at temperatures up to 250 °C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses. The results show that H2O does not reduce NO and NH3 adsorption on V2O5/AC catalyst surface, but promotes NH3 adsorption due to increases in Bronsted acid sites. Many kinds of NH3 forms present on the catalyst surface, but only NH4+ on Bronsted acid sites and a small portion of NH3 on Lewis acid sites are reactive with NO at 250 °C or below, and most of the NH3 on Lewis acid sites does not react with NO, regardless the presence of H2O in the feed gas. H2O inhibits the SCR reaction between the NH3 on the Lewis acid sites and NO, and the inhibition effect increases with increasing H2O content. The inhibition effect is reversible and H2O does not poison the V2O5/AC catalyst.

Qingya Liu

Papers

Characterization of submicron aerosols during a month of serious pollution in Beijing, 2013

Formation and reaction of ammonium sulfate salts on V2O5/AC catalyst during selective catalytic reduction of nitric oxide by ammonia at low temperatures

Simultaneous removal of SO2 and NOx from flue gas using a CuO/Al2O3 catalyst sorbent: I. Deactivation of SCR activity by SO2 at low temperatures

Inhibition effect of H2O on V2O5/AC catalyst for catalytic reduction of NO with NH3 at low temperature

Performance of an activated carbon honeycomb supported V2O5 catalyst in simultaneous SO2 and NO removal