مدل‎سازی مکانی ـ زمانی سه‎بعدی پراکنش آلاینده‌ی اکسیدهای ازت هوا ناشی از ترافیک در تقاطع خیابان ولی‌عصر ـ فاطمی شهر تهران

یکی از مشکلات اصلی شهرها افزایش سریع آلودگی هواست که ترافیک وسایل نقلیه یکی از مهم ترین عوامل آن به شمار می رود. مدیریت هدفمند این عامل آلوده کننده نیازمند اطلاعات صحیح و دقیق از نحوه ی انتشار آلاینده ها در شرایط گوناگون مکانی و زمانی است. در این باره، پژوهش حاضر نحوه ی انتشار سه بعدی آلودگی حاصل از اکسیدهای نیتروژن (nox) را در مقیاس میکرو بررسی و با استفاده از مدل gral محدوده ی تقاطع ولی عصر ـ فاطمی شهر تهران را در فصل زمستان مطالعه می کند. با توجه به این، خودروها به منزله ی مهم ترین عامل آلاینده به مدل معرفی شد و فرآیند مدل سازی در نُه ارتفاع متفاوت (از 1.7 تا 52.5 متری) انجام گردید. برای بررسی ویژگی های فضایی و زمانی داده های میزان غلظت آلاینده ی nox از روش های خودهم بستگی فضایی عمومی و محلی موران استفاده گردید. میزان شاخص موران معادل 0.7 تا 0.9 در حالت دوبعدی و معادل 0.22 در حالت سه بعدی در نتایج حاصل نشان دهنده ی وجود سطح بالایی از خود هم بستگی فضایی مثبت معنادار است که گواه صحت عملکرد شبیه سازی صورت گرفته است. تحلیل شاخص موران محلی/انسلین نشان دهنده ی غلبه ی نقاط بالا ـ بالا در ارتفاعات پایین تا متوسط و افزایش نقاط پایین ـ پایین در ارتفاع های بالاتر است. همچنین، وجود خوشه های آلودگی نسبتاً پایدارتر در ارتفاع های مختلف در تقاطع ها و ناپایداری وضعیت خوشه بندی آلودگی هوا در نزدیکی ساختمان ها در نتایج حاصل مشهود است.

3D Spatio-Temporal Modeling of NOx Air Pollution of Vehicular Traffic in Vali-e-Asr and Fatemi Streets Intersection, Tehran City

Air pollution has become one of the main problems of cities. Among the sources of air pollution, vehicular traffic plays an important role. Planning for efficient management and control of the air pollution caused by vehicular traffic requires accurate information on spatiotemporal dispersion of the pollutions. This research studies 3D spatiotemporal dispersion of NOx pollution caused by vehicular traffic at ValieasrFatemi intersection resides in Tehran, Iran. It is selected for being crowded and having the required meteorological and pollution data sensed by the Air Quality Control Corp. of Tehran Municipality.This study uses GRAL that is a local microscale air dispersion model defined based on EuleranLagrangian dispersion models. It investigates the level of spatiotemporal autocorrelation generated by GRAL simulations at both 2D and 3D modes and discusses how it adapts with the reality.Adopting the GRAL air pollution dispersion model, streets are defined as the linear source of pollution of NOx caused by vehicular traffic. The traffic rate is estimated based on street areas and directions, the designed average traffic velocity, traffic volume and car passage counting at the intersection. The 3D geometry of the buildings is also added to the model. All the required data that were available for winter of 2007 are gathered and introduced into the model.The model is executed at 9 heights vary from 1.7 m to 52.5 m. These heights are defined covering a range from an average human level height to average building height and above. These levels are considered both separately in 2D mode and integrated into a 3D mode. The formation of NOx clusters is investigated analyzing their autocorrelation using Moran Index at global and local scale.The calculated MoranI at global scale at each 9 levels of heights, varies from 0.7 to 0.9 that depicts the validity of the GRAL model adopted to simulate the expected autocorrelation of pollution density affected by spatial issues. The MoranI increases at higher levels as less air turbulence happens. However the result show that the turbulence increases temporarily at about 10m to 15m which are the average building heights. At local scale, the MoranI/Anselin shows that HH clusters dominate at lower levels, around streets central areas that are farther from the buildings, and around the intersections. At higher levels, esp. higher than buildings average height, the LL clusters dominate. However the HH clusters formed around intersections, while are shrank, are still visible at high levels. The turbulence caused by building fronts and their down wash effect is also shown in the result as no definite cluster is formed near the buildings front and back.The autocorrelation analysis is also carried for an integrated 3D model consists of all the 9 levels of heights. Considering the weight matrix for a 20m 2D neighborhood and 1m/s dispersion of the pollution vertically, the global calculated MoranI equals 0.229 which shows existence of a spatiotemporal autocorrelation of the results generated by GRAL. At local scale the results show that the HH clusters have higher temporal dispersion rate than LL clusters.