Shili Tian

Size-resolved aerosol chemical analysis of extreme haze pollution events during early 2013 in urban Beijing, China

Using size-resolved filter sampling and chemical characterization, high concentrations of water-soluble ions, carbonaceous species and heavy metals were found in both fine (PM2.1) and coarse (PM2.1-9) particles in Beijing during haze events in early 2013. Even on clear days, average mass concentration of submicron particles (PM1.1) was several times higher than that previously measured in most of abroad urban areas. A high concentration of particulate matter on haze days weakens the incident solar radiation, which reduces the generation rate of secondary organic carbon in PM1.1. We show that the peak mass concentration of particles shifted from 0.43-0.65μm on clear days to 0.65-1.1μm on lightly polluted days and to 1.1-2.1μm on heavily polluted days. The peak shifts were also found for the following species: organic carbon, elemental carbon, NH4(+), SO4(2-), NO3(-), K, Cu, Zn, Cd and Pb. Our findings demonstrate that secondary inorganic aerosols (36%) and organic matter (26%) dominated the fine particle mass on heavily polluted days, while their contribution reduced to 29% and 18%, respectively, on clear days. Besides fine particles, anthropogenic chemical species also substantially accumulated in the coarse mode, which suggests that particles with aerodynamic diameter larger than 2.1μm cannot be neglected during severe haze events.

The Campaign on Atmospheric Aerosol Research Network of China: CARE-China

AbstractBased on a network of field stations belonging to the Chinese Academy of Sciences (CAS), the Campaign on Atmospheric Aerosol Research network of China (CARE-China) was recently established as the country’s first monitoring network for the study of the spatiotemporal distribution of aerosol physical characteristics, chemical components, and optical properties, as well as aerosol gaseous precursors. The network comprises 36 stations in total and adopts a unified approach in terms of the instrumentation, experimental standards, and data specifications. This ongoing project is intended to provide an integrated research platform to monitor online PM2.5 concentrations, nine-size aerosol concentrations and chemical component distributions, nine-size secondary organic aerosol (SOA) component distributions, gaseous precursor concentrations (including SO2, NOx, CO, O3, and VOCs), and aerosol optical properties. The data will be used to identify the sources of regional aerosols, the relative contributions fr...

Reply to Comment on “Fossil Fuel Combustion-Related Emissions Dominate Atmospheric Ammonia Sources during Severe Haze Episodes: Evidence from 15N-Stable Isotope in Size-Resolved Aerosol Ammonium”

Dominate Atmospheric Ammonia Sources during Severe Haze Episodes: Evidence from N‐Stable Isotope in Size-Resolved Aerosol Ammonium” W appreciate the opportunity to respond to the comments of Chang and Ma regarding our article, and we also hope to further clarify the findings of our work. Their comments on our work focus on the source apportionment of ammonia (NH3) during haze episodes in Beijing. We do not think that their objections are well founded, and their speculations do not change our conclusions.

Size-resolved aerosol trace elements at a rural mountainous site in Northern China: importance of regional transport.

This paper presents an intensive field measurement campaign carried out at the rural mountainous site of Xinglong (960 m a.s.l.) in Northern China during Sep. 3-20 2008. Size-segregated samples were collected daily and analyzed for 25 trace elements (TEs). The majority of the TEs showed comparable concentrations in fine (<2.1 μm) and coarse particles (2.1-9 μm). In addition, elements like K, Mn, Cu, Se, Mo, Ag, Cd, Tl and Pb were accumulated in fine mode whereas Al, Co and Sb were concentrated in a coarse mode. For most of the TEs, their enrichment factor (EF) increased with decreasing particle size from large (>9 μm) to coarse, and to fine, signifying influences by anthropogenic emissions. The observed concentrations of heavy metals in fine particles, with EF values higher than 100, were significantly higher than the historical data recorded in the 1980s and 1990s, reflecting the increasing emissions in the target area. One pronounced event occurred on Sep. 14 when all of the TEs showed a peak, which was associated with regional emissions from both southeast (SE) and southwest (SW) indicated by backward trajectory analysis. This is further supported by the measurements in upwind sites where the concentrations of TEs were several times higher than those in Xinglong, suggesting potential source regions. Episodes of heavy metals were generally characterized by significant enhancements of fine mode and air mass trajectories from SE or SW alone. Taking this finding and factor analysis results together, the metallic episodes were attributable to the long-range transport of regional plumes from coal consumption and nonferrous metal smelting. With the rapid urbanization and industrialization in Northern China, the increasing emissions of TEs will place a great strain on human health and the environment in the downwind regions, thus long-term and multi-site observation with high time resolution are necessary.

Trace elements in particulate matter from metropolitan regions of Northern China: Sources, concentrations and size distributions.

Public concerns over airborne trace elements (TEs) in metropolitan areas are increasing, but long-term and multi-site observations of size-resolved aerosol TEs in China are still lacking. Here, we identify highly elevated levels of atmospheric TEs in megacities and industrial sites in a Beijing-Tianjin-Hebei urban agglomeration relative to background areas, with the annual mean values of As, Pb, Ni, Cd and Mn exceeding the acceptable limits of the World Health Organization. Despite the spatial variability in concentrations, the size distribution pattern of each trace element was quite similar across the region. Crustal elements of Al and Fe were mainly found in coarse particles (2.1-9 μm), whereas the main fraction of toxic metals, such as Cu, Zn, As, Se, Cd and Pb, was found in submicron particles (<1.1 μm). These toxic metals were enriched by over 100-fold relative to the Earths crust. The size distributions of Na, Mg, K, Ca, V, Cr, Mn, Ni, Mo and Ba were bimodal, with two peaks at 0.43-0.65 μm and 4.7-5.8 μm. The combination of the size distribution information, principal component analysis and air mass back trajectory model offered a robust technique for distinguishing the main sources for airborne TEs, e.g., soil dust, fossil fuel combustion and industrial emissions, at different sites. In addition, higher elemental concentrations coincided with westerly flow, indicating that polluted soil and fugitive dust were major sources of TEs on the regional scale. However, the contribution of coal burning, iron industry/oil combustion and non-ferrous smelters to atmospheric metal pollution in Northern China should be given more attention. Considering that the concentrations of heavy metals associated with fine particles in the target region were significantly higher than those in other Asian sites, the implementations of strict environmental standards in China are required to reduce the amounts of these hazardous pollutants released into the atmosphere.

Identifying Ammonia Hotspots in China Using a National Observation Network

The limited availability of ammonia (NH3) measurements is currently a barrier to understanding the vital role of NH3 in secondary aerosol formation during haze pollution events and prevents a full assessment of the atmospheric deposition of reactive nitrogen. The observational gaps motivated us to design this study to investigate the spatial distributions and seasonal variations in atmospheric NH3 on a national scale in China. On the basis of a 1-year observational campaign at 53 sites with uniform protocols, we confirm that abundant concentrations of NH3 [1 to 23.9 μg m-3] were identified in typical agricultural regions, especially over the North China Plain (NCP). The spatial pattern of the NH3 surface concentration was generally similar to those of the satellite column concentrations as well as a bottom-up agriculture NH3 emission inventory. However, the observed NH3 concentrations at urban and desert sites were comparable with those from agricultural sites and 2-3 times those of mountainous/forest/grassland/waterbody sites. We also found that NH3 deposition fluxes at urban sites account for only half of the emissions in the NCP, suggesting the transport of urban NH3 emissions to downwind areas. This finding provides policy makers with insights into the potential mitigation of nonagricultural NH3 sources in developed regions.

Wet deposition and scavenging ratio of air pollutants during an extreme rainstorm in the North China Plain

Abstract Atmospheric wet deposition plays an important role in the supply of nutrients and toxic substances to terrestrial and aquatic environments. Although long-term (e.g. annual, multi-year) wet deposition is recorded well, pronounced and short-term changes in precipitation chemistry are less well investigated. In the present study, the precipitation chemistry and scavenging ratio of air pollutants were observed during an extreme torrential rain event (325.6 mm at the observation site) that occurred over 19–21 July 2016 in the North China Plain (NCP). The scavenging ratio of particles showed a similar spatial distribution to that of the precipitation amount in the NCP, indicating the efficient removal of particulate matter due to the large amount and precipitation intensity of the storm. In addition, the scavenging ratio of water soluble ions was larger than that of organics and gaseous pollutants such as SO2 and NO2, likely due to their differences in water solubility. Consequently, raindrops incorporated more aerosol sulfate than gaseous compounds. Due to the heavy precipitation amount, almost all species in rainwater during this storm showed their lowest concentration but the highest flux compared with other rain events, indicating an important role played by this storm in terms of the substances received by the terrestrial and marine ecosystems of the region. However, the contribution of this storm to the annual chemical flux was lower than that of precipitation amount, indicating that the atmospheric compounds were scavenged below-cloud first and were then diluted by the cloud/rainwater. Future studies are needed in the context of the occurrence of extreme rainfall events in the NCP from the perspective of climate variability.