PM_(2.5) in China:Measurements,sources,visibility and health effects,and mitigation

Concern over the health effects of fine particles in the ambient environment led the U.S. Environmental Protection Agency to develop the first standard for PM2.5 （particulate matter less than 2.5 μm） in 1997. The Particle Technology Laboratory at the University of Minnesota has helped to establish the PM2.5 standard by developing many instruments and samplers to perform atmospheric measurements. In this paper, we review various aspects of PM2.5, including its measurement, source apportionment, visibility and health effects, and mitigation. We focus on PM2.s studies in China and where appropriate, compare them with those obtained in the U.S. Based on accurate PM2.5 sampling, chemical analysis, and source apportionment models, the major PM2.5 sources in China have been identified to be coal combustion, motor vehicle emissions, and industrial sources. Atmospheric visibility has been found to correlate well with PM2.s concentration. Sulfate, ammonium, and nitrate carried by PM2.s, commonly found in coal burning and vehicle emissions, are the dominant contributors to regional haze in China. Short-term exposure to PM2.s is strongly associated with the increased risk of morbidity and mortality from cardiovascular and respiratory diseases in China. The strategy for PMzs mitigation must be based on reducing the pollutants from the two primary sources of coal-fired power plants and vehicle emissions. Although conventional Particulate Emission Control Devices （PECD） such as electrostatic precipitators in Chinese coal-fired power plants are generally effective for large particles, most of them may not have high collection efficiency of PM2.5. Baghouse filtration is gradually incorporated into the PECD to increase the PM2.5 collection efficiency. By adopting stringent vehicle emissions standard such as Euro 5 and 6, the emissions from vehicles can be gradually reduced over the years. An integrative approach, from collaboration among academia, government, and industries, can effectively manage and mitigate the PM2.s pollution in China.

Integrative filtration research and sustainable nanotechnology

With the wide applications of nanomaterials in an array of industries, more concerns are being raised about the occupational health and safety of nanoparticles in the workplace, and implications ofnanotech- nology on the environment and living systems. Studies on environmental, health and safety （EHS） issues of nanomaterials play a significant role in public acceptance, and eventual sustainability, of nanotechnol- ogy. We present research results on three aspects of the EHS studies： characterization and measurement of nanoparticles, nanoparticle emission and exposure at workplaces, and control and abatement of nanoparticle release using filtration technology. Measurement of nanoparticle agglomerates using a newly developed instrument, the Universal Nanoparticle Analyzer, is discussed. Nanoparticle emission and exposure measurement results for carbon nanotubes in the manufacture of nanocomposites and for silicon nanoparticles in their production at a pilot scale facility are presented. Filtration of nanoparticles and nanoparticle agglomerates are also studied.

Great wall of solar panels to mitigate yellow dust storm

Mitigation of the large scale yellow dust storm is a serious problem facing China. We propose the approach of building windbreak walls equipped with solar panels in the proximity of dust origins. The solar panels generate electricity in the sunny days; the walls break the wind and remove airborne dusts based on the impactor principle during wind storms. Preliminary calculation indicates the walls may be able to remove the major fraction of the airborne dusts and the generated electricity could be significant. More detailed studies are needed to prove the feasibility of the approach.

Reply to the comment

We are grateful for the experts＇ comments on our manuscript. We fully understand the experts＇ concerns on the feasibility of the proposed idea of building windbreak walls equipped with solar panels to mitigate the yellow dust storm. As stated in the manuscript, we have not considered many important factors, such as the limits posed by solar panels, operability of solar panels under harsh conditions, the local weather and geomorphological conditions, electricity storage and transportation, financial aspects, etc. However, the manuscript is intended to present a Big Idea to stimulate more interesting ideas to solve Big Problems.