Abstract As the particulate-matter (PM) emission standards in China become increasingly rigorous (their upper limit has decreased to 10 mg/m3 in the power industry), considerable attention has been paid to PM emissions from coal-fired power plants. However, there is a large amount of water vapour in flue gas from power plants, which poses a great challenge to the measurement of the PM mass concentration via light scattering. Although water vapour does not affect the light scattering, changes in the properties of particles caused by water vapour influence it. To investigate the effects of the aerosol relative humidity on the PM mass-concentration measurement via light scattering, a test rig was constructed for wet aerosol light-scattering measurements. Light-scattering and hygroscopic properties, as well as morphological features of fly ash aerosol and pure mineral aerosol (pure powder silica) under different relative-humidity conditions were compared in a laboratory. The linear least-squares method was used to fit the relationship between the scattered light intensity and the PM mass concentration under four different humidity conditions. With increase in relative humidity, the R-squared values and the slopes of the fitted line were 0.9941, 0.9941, 0.9926, and 0.9854 and 35.14, 35.90, 28.59, and 26.91, respectively. Thus, the intensity of light scattering was directly proportional to the PM mass concentration, and the mass sensitivity, i.e. the slope of the fitted curve, changed with respect to relative humidity. From low to high relative-humidity conditions, the enhancement factors at a scattering angle of 20° were 0.868 ± 0.045, 0.814 ± 0.053, and 0.706 ± 0.029 for powder silica and 0.905 ± 0.010, 0.918 ± 0.015, and 0.984 ± 0.019 for fly ash. Thus, humidity had a greater influence on the mass-concentration measurement of powder silica aerosol via light scattering than on that of fly ash aerosol. Scanning electron microscopy results for aerosol particles under different humidity conditions indicated that the agglomeration characteristics of these particles increased with the relative humidity. Considering previous reports on the response characteristics of the hygroscopic particles with respect to their optical properties to relative humidity in the atmosphere, we found that the hygroscopic growth and agglomeration of aerosol particles together determine the measurement accuracy, which is very useful for onsite measurements of the PM mass concentration via the light-scattering method.

中文翻译：

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相对湿度对通过光散射实时测量颗粒物浓度的影响

摘要 随着我国颗粒物（PM）排放标准的日益严格（电力行业其上限已降至10 mg/m3），燃煤电厂的PM排放受到越来越多的关注。然而，电厂烟气中含有大量的水蒸气，这对通过光散射测量PM质量浓度提出了很大的挑战。虽然水蒸气不影响光散射，但由水蒸气引起的粒子性质的变化会影响它。为了通过光散射研究气溶胶相对湿度对 PM 质量浓度测量的影响，构建了一个测试台用于湿气溶胶光散射测量。光散射和吸湿性，并在实验室比较了不同相对湿度条件下粉煤灰气溶胶和纯矿物气溶胶（纯粉二氧化硅）的形态特征。采用线性最小二乘法拟合四种不同湿度条件下散射光强度与PM质量浓度之间的关系。随着相对湿度的增加，R 平方值和拟合线的斜率分别为 0.9941、0.9941、0.9926 和 0.9854 和 35.14、35.90、28.59 和 26.91。因此，光散射强度与 PM 质量浓度成正比，质量灵敏度，即拟合曲线的斜率，随相对湿度而变化。从低到高的相对湿度条件下，20°散射角处的增强因子为0.868±0.045，0。粉状二氧化硅为 814 ± 0.053 和 0.706 ± 0.029，粉煤灰为 0.905 ± 0.010、0.918 ± 0.015 和 0.984 ± 0.019。因此，与粉煤灰气溶胶相比，湿度对光散射粉末二氧化硅气溶胶质量浓度测量的影响更大。不同湿度条件下气溶胶颗粒的扫描电镜结果表明，这些颗粒的团聚特性随着相对湿度的增加而增加。考虑到先前关于吸湿颗粒的光学特性对大气中相对湿度的响应特性的报告，我们发现气溶胶颗粒的吸湿生长和团聚共同决定了测量精度，