中国与世界,环境危机大家谈

china and the world discuss the environment

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allegrini

加入本网站时间 Member Since 23 December 2011

Allegrini's 评论 comments

美国大使馆的PM2.5测量值

这非常令人奇怪。在我从事空气质量技术与科学研究41年后,在21世纪第二个十年的刚开始的今天,当我看到一份出自史蒂文•安德鲁先生的报告之后觉得很不舒服,安德路先生好像是匆匆一瞥就尽数了解一座大型城市的空气污染问题。

但是,这位自封的专家所面临的第一个问题就是:我们能否确信架在美国人屋顶的监测设备具备所必需的准确度和精密度呢?我们能否确信那些数据表格经得起合理的质疑和推敲呢?这方面,恰恰应该是空气质量监测优先考虑的事情,却被安德路先生一句简单的“这台设备是唯一经过美国国家环保署认证用于监测PM2.5的设备”所带过。我无意于卷入美国国家环保署(该机构负责认证工作)的内部事务。我仅限于自己想指出的是认证并不是绝对的,然而为了有效,设备也必须遵循特定的规范以保证数据的有效性。我担心,在北京,这些规范远没有得到该有的尊重。

以北京的天气条件,空气质量重度污染现象都是在大雾条件下发生。现在,利用β射线吸收法(用于BAM仪器)对颗粒物的监测对水分子具有极高的敏感性,因为水分子中氢元素的质量百分比约为10%。由于水分子中氢的Z(原子序数)/M(分子质量)(氢的Z/M值为1,一般元素的Z/M值都是0.5)值比较高,β射线的吸收率也就高。这也就意味着被检测的颗粒物,如果在采样器的进气通道没有完全的去除水分,PM2.5的读数将会比真正的浓度数值有大幅度的增加。

显然,制造并销售此设备的公司提供了去除水雾的附件装置;然而,并没有提供该装置在不同环境下有关效率的技术信息,例如在北京,颗粒物的物理特性几乎是独一无二的。总之,我强烈怀疑美国使馆屋顶上的监测设备所监测到的PM2.5中含有大量的水雾。但是,我只会在掌握了水雾在监测过程中被有效消除的真实证据后才将重新考虑我的立场。

最后,请您不要援引美国国家环保署的认证与规范。众所周知,美国环保局认证的一款PM10监测仪已在欧洲(当然也在美国)销售了上成千上万台,却被证实具有大量丢失颗粒物的特性,有时这种丢失量大于50%。只有少数人意识到这一点。发现这点后,设备制造商试图用一个昂贵的附属设备解决该问题。这个片段也帮助很多人明白,空气污染监测不是一件容易的事情,解决问题时也并不像问题出现时那么简单,也表明美国的同事们有时也会犯错误。

最后,我相信美国在环境监测技术上所收获的教训意义重大,我们也要看到这个伟大国家在技术和科技发展中积极的一面。然而,一些代表这个伟大国家的人们也应该遵循起码的谦逊,尽管发生在一些国家的事情不那么“伟大”。

当安德鲁先生去除掉围绕在监测仪器周围的雾气,并得出浓度数据的时候,或许我将对这篇的文章剩下的部分做出评论。

伊万•阿里格里尼
环境专家
罗马“La Sapienza”大学
[email protected]
Tel. (+39) 335 462208

US Embassy's PM2,5 measurements

It is very suprising. I've been engaged into the technology and reseaches on air quality for 41 years, on the day of the very beginning of the second ten years of 21 century, I felt uncomfortable as I read a report by Steven Q Andrews, who seems to know the giant city's air pollution well just with a glimpse.

However, the very first problem came to the self-appointed expert is:whether we can guarantee the device atop the US ambessary is qualified as required in terms of accuracy and whether we can secure the statistics and graphs be true against reasonable doubts and deliberations, which is, in priority, taken into account in air quality monitoring and which is prevaricated by Mr. Andrews as the monitor "is the only continuous particulate monitor that the US Environmental Protection Agency allows for PM 2.5 monitoring in the United States". I don't intend to be involved in the internal business of USA Environmental Protection Agency, who take charge of the business of authentication. What I want to say, only in my own opinion, is the authentication is not absolute, but for the sake of effectiveness of the statistics, the devices have to be in compliance with certain specifications. It is my concern that the specifications do not deserve the respect as it should in Beijing.

All the heavily-pulluted phenomenon of air quality in the states-quo Beijing generate under the condition of heavy fog. Currently, the monitoring survey on particulate matters adopting particuleβabsorptiometry is highly sensitive to water melocules, becuase hydrogen accounts for part of a melocule as around 10% in terms of quality. The higer Z(atomic number)/M(melocular weight) (the value of Z/M of hydrogen is 1, while that of common chemical elements is 0.5) of hydrogen in water melocule the higer absorbing rate of particuleβ. This means the value of PM2.5 would increse substantially to be higher than the actual one once the moisture in the particulates detected was not deprived in the entrance of the sampler.

Obviously, the monitor supplier offers the attached de-moisturation unit but without the information on various efficiencies in different environments. Take Beijing for example, the physical features of the particulate matters are almost unique. All in all, I'm strongly doubting the PM2.5 detected by the monitor atop the US ambessy involve large quantity of water mist. Yet, I won't reconsider my stand point of view until I am given the real evidence that the water mist is deprived efficiently during the survey.

Final but not least, do not quote the authentication of USA Environmental Protection Agency and the specifications by it. As known to all, the hundreds of thousands of a model of PM10 monitor approved by the agency been sold in Europe (in US as well, of course) have been proven to be featured with losing particulate matters in large quantity, sometimes the losing is over 50%. Few people were aware of this defect. The manufacturer tried to addressing this problem by adding a extra unit onto the monitor after the exposure of the defect. This episode helps many understand it is not a walk in the garden to do monitoring survey on air pollution either a piece of cake to resolve issues as they occur. As well, this interprets the US fellows would make mistakes sometimes.

Finally, I believe the lessons acquried by the USA on environment monitoring survey are of great meaningful. We have to be aware of the positive aspect of this great nation on the development of techniques, science and technology. Yet, some on behalf of this nation should follow the least spirit of modesty while some events undertaking in some nations are not so "great".

Maybe I would not issue my discussion on the rest of the text until Mr. Andrews got rid of the moisture embracing the monitor and gained the density statistics.

Ivo Allegrini
environmentalist

La Sapienza University in Rome
[email protected]
Tel. (+39) 335 462208

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