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有标准对流层NO2水平被认为是低还是高?

我工作与臭氧监测仪)$ \ ce {NO_2} $垂直列密度(分子/厘米²)数据。帮助解释值,我想知道如果有标准显示的值被认为是低和高,或好的vs危险(类似于空气质量指数/ AQI)。有任何机构(例如,EPA,欧盟发表任何有关呢?

回答

OMI对流层NO2检索算法并不提供表面NO2浓度,而是一个列密度。所以,不适合直接对应那些OMI检索卫生标准是基于环境浓度的表面。有很多尝试对流层NO2表面NO2浓度相关,但相关性是公平的。此外,对流层列固有的变化取决于高程,因为大气对流层列的数量减少,地表高程增加。还有几个假设进入检索创建大量的错误(例如平流层列减法,先天* *档案、表面反照率,等等)。正如我在这篇文章[1],讨论可以区分清洁,污染,高度污染的对流层NO2列。然而,精确的阈值是特定于位置,有时季节,由于检索算法不同的响应取决于参数的假设。一般来说,如果你看到值~ 5 x10 ^ ^ 15 molec /厘米2,可以肯定的是有真正的NO2污染。任何超过x10 ^ ^ 16 molec /厘米2是高度污染的。值越高,越有信心的检索。 You can see the responses from the creators of OMI for similar questions [here][2]: >**Does the red colour signal smog at the surface?** >No, since OMI does not measure the concentration at the surface directly. Instead, OMI measures the total amount of nitrogen dioxide (NO2) in a column up to about 10 km. >However, research has shown that high NO2 column amounts in OMI measurements (red colours) usually coincide with high concentration levels at the surface. This concentration is usually not as high that you can it moderate or heavy smog, but it does still indicates an elevated level of air pollution. The OMI measurements clearly show that The Netherlands suffers from a significantly higher level of air pollution by NO2. See also the answers to the next questions. Note that smog does not exist only of NO2. Other important ingredients are aerosols, ozone, sulphur dioxide and hydro carbons. >**The OMI map shows a red colour over The Netherlands but according to surface measurements of the Dutch National Institute of Public Health and the Environment (RIVM) it just minor smog. What causes the difference?** >The surface measurements from RIVM are related to the European norms for smog. Those norms are related to a peak level surface concentration. The threshold level is an average concentration of 200 microgram/m3 NO2 during one hour. The peak levels should not exceed this threshold more than 18 hours per year. Peak levels concentrations are most of the time well below the threshold values and therefore one speaks of minor smog. OMI does not measure the concentration at the surface directly. Instead, OMI measures the total amount of nitrogen dioxide (NO2) in a column up to about 10 km. For this column amount there are no direct European norms. The relation between column amounts as measured by satellites and surface concentrations is complicated. Therefore, a red coloured area in the OMI map cannot be related directly to European norms and no conclusion with respect to exceeding some norm can be drawn from the OMI maps. The colours in the OMI maps are chosen in such a way that you can clearly see the difference between different areas. Column amounts of 20 x 10 power 15 molecules per cm2 and higher all have same red-purple colour. >**Can OMI measurements be related to ground level concentrations, like those being measured by the Dutch National Institute of Public Health and the Environment (RIVM)?** >The largest contribution to the measured NO2 column amount is located in the boundary layer. This is the bottom layer of the atmosphere in which air is mixed quite rapidly and in which the NO2 concentrations are relatively constant. The height of boundary layer varies between a few hundred meters till a few kilometres. The height varies during the day and depends on the weather and season of the year. A rough estimate of the NO2 surface concentration can be calculated by dividing the column amount with the height of the boundary layer. A study, using a chemical model of the atmosphere, showed that NO2 measurements by satellites are consistent with surface measurements and that the red-purple coloureds area roughly have surface concentration of 40 microgram/m3 NO2. This value is similar to the European threshold norm for the year-average concentration. [1]: //www.hoelymoley.com/questions/9108/the-higher-value-range-for-the-same-satellite-product-no2-omi-temis?rq=1 [2]: http://projects.knmi.nl/omi/news/temis/faq_nrt_trop_no2.html#smog-1

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