Purpose

Tehran, Iran, is an interesting location for aerosol studies because it is affected by anthropogenic pollution and desert dust aerosols. The aim of this study was to discriminate the aerosol types using satellite data over the city.

Method

The study was performed using Level-2 daily Aerosol Optical Depth (AOD) and Ångström Exponent (AE) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board the Terra and Aqua satellites for the years 2011 to 2015. As the Deep Blue (DB) AE retrievals are more reliable than the Dark Target (DT) AE retrievals, the study was performed using DB data.

Results

The number of granules with successful retrievals (at least in two pixels with AODs >0.2 over Tehran with high quality assurance) was 200, which indicates that aerosols could be observed in 5.47% (200 from 3652 of Terra and Aqua granules) of the overpasses during the study period. The maximum and minimum values of AOD occurred during May (0.32 ± 0.27) and August (0.18 ± 0.07), respectively. Based on the AOD vs. AE data, aerosols were classified into three different categories: urban/industry (UI), Desert Dust (DD) and Mixed (Mix). To improve the accuracy of the aerosol classification, the analysis was limited to retrievals with AOD values larger than 0.2. The DD, UI and Mix types had 48.5%, 30.5% and 21% contribution in the aerosol days, respectively.

Conclusions

The maximum DD frequency was observed in the spring and summer seasons, while the UI type had its maximum during the cold season. The AOD of the DD type (over Tehran) correlated well with the AOD observations done at the Aerosol Robotic Network (AERONET) site in Zanjan (300 km northwest from Tehran). For the UI type, no relationship with the AERONET AOD was detected. This gives confidence in our aerosol typing as the contribution of dust in the aerosol load is mainly from long-range transport, whereas the urban aerosols originate from local sources. Back trajectories ending in Tehran show that the northeast and west trajectories are two main transport routes for the dust to the study area.

中文翻译：

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使用 5 年（2011-2015 年）MODIS 收集 6 种气溶胶产品对德黑兰市的气溶胶类型进行区分。

目的

伊朗德黑兰是气溶胶研究的一个有趣地点，因为它受到人为污染和沙漠尘埃气溶胶的影响。本研究的目的是利用城市上空的卫星数据来区分气溶胶类型。

方法

该研究使用 2011 年至 2015 年 Terra 和 Aqua 卫星上的中分辨率成像光谱辐射计 (MODIS) 仪器的 2 级每日气溶胶光学深度 (AOD) 和 Ångström 指数 (AE) 数据进行。作为深蓝(DB) AE 检索比暗目标 (DT) AE 检索更可靠，该研究是使用 DB 数据进行的。

结果

成功检索的颗粒数量（至少在两个像素中，AOD > 0.2 且质量保证在德黑兰上空）为 200，这表明可以在 5.47% 的立交桥中观察到气溶胶（Terra 和 Aqua 颗粒的 3652 中的 200 个）在学习期间。AOD 的最大值和最小值分别发生在 5 月 (0.32 ± 0.27) 和 8 月 (0.18 ± 0.07) 期间。根据 AOD 与 AE 数据，气溶胶分为三个不同的类别：城市/工业 (UI)、沙漠尘埃 (DD) 和混合 (Mix)。为了提高气溶胶分类的准确性，分析仅限于 AOD 值大于 0.2 的检索。DD、UI 和 Mix 类型在气溶胶天数中的贡献分别为 48.5%、30.5% 和 21%。

结论

DD 频率最高出现在春夏季节，而 UI 类型在寒冷季节最高。DD 型（德黑兰上空）的 AOD 与在赞詹（距德黑兰西北 300 公里）的气溶胶机器人网络 (AERONET) 站点进行的 AOD 观测具有很好的相关性。对于 UI 类型，未检测到与 AERONET AOD 的关系。这使我们对我们的气溶胶分类充满信心，因为灰尘在气溶胶负荷中的贡献主要来自远程传输，而城市气溶胶则来自本地来源。以德黑兰为终点的回溯轨迹表明，东北和西部轨迹是尘埃进入研究区的两条主要运输路线。