Hu Shishan, Fruin Scott, Kozawa Kathleen, Mara Steve, Paulson Suzanne E, Winer Arthur M
Environmental Health Sciences Department, School of Public Health, 650 Charles E. Young Drive South, University of California, Los Angeles, CA 90095-1772, USA ; Department of Atmospheric and Oceanic Sciences, 405 Hilgard Ave., University of California, Los Angeles, CA 90095-1565, USA.
Preventive Medicine, Environmental Health Division, Keck School of Medicine, University of Southern California, 1540 Alcazar Street CHP-236 Los Angeles, CA 90032, USA.
Atmos Environ (1994). 2009 May 1;43(16):2541-2549. doi: 10.1016/j.atmosenv.2009.02.033.
We have observed a wide area of air pollutant impact downwind of a freeway during pre-sunrise hours in both winter and summer seasons. In contrast, previous studies have shown much sharper air pollutant gradients downwind of freeways, with levels above background concentrations extending only 300 m downwind of roadways during the day and up to 500 m at night. In this study, real-time air pollutant concentrations were measured along a 3 600 m transect normal to an elevated freeway 1-2 hours before sunrise using an electric vehicle mobile platform equipped with fast-response instruments. In winter pre-sunrise hours, the peak ultrafine particle (UFP) concentration (95 000 cm) occurred immediately downwind of the freeway. However, downwind UFP concentrations as high as ~ 40 000 cm extended at least 1 200 m from the freeway, and did not reach background levels (15 000 cm) until a distance of about 2 600 m. UFP concentrations were also elevated over background levels up to 600 m upwind of the freeway. Other pollutants, such as NO and particle-bound polycyclic aromatic hydrocarbons, exhibited similar long-distance downwind concentration gradients. In contrast, air pollutant concentrations measured on the same route after sunrise, in the morning and afternoon, exhibited the typical daytime downwind decrease to background levels within ~300 m as found in earlier studies. Although pre-sunrise traffic volumes on the freeway were much lower than daytime congestion peaks, downwind UFP concentrations were significantly higher during pre-sunrise hours than during the daytime; UFP and NO concentrations were also strongly correlated with traffic counts on the freeway. We associate these elevated pre-sunrise concentrations over a wide area with a nocturnal surface temperature inversion, low wind speeds, and high relative humidity. Observation of a wide air pollutant impact area downwind of a major roadway prior to sunrise has important exposure assessment implications since it demonstrates extensive roadway impacts on residential areas during pre-sunrise hours, when most people are at home.
我们在冬季和夏季的日出前时段，观测到高速公路下风方向存在大面积的空气污染物影响区域。相比之下，先前的研究表明高速公路下风方向的空气污染物梯度更为陡峭，白天道路下风方向浓度高于背景浓度的区域仅延伸至道路下风300米处，夜间则可达500米。在本研究中，使用配备快速响应仪器的电动车辆移动平台，在日出前1 - 2小时沿着与高架高速公路垂直的3600米横断面测量实时空气污染物浓度。在冬季日出前时段，超细颗粒物（UFP）浓度峰值（约95000个/立方厘米）出现在高速公路紧邻下风处。然而向下风方向，UFP浓度高达约40000个/立方厘米的区域至少从高速公路延伸了1200米，直到距离约2600米处才达到背景水平（约15000个/立方厘米）。在高速公路上风方向600米范围内，UFP浓度也高于背景水平。其他污染物，如一氧化氮和颗粒结合的多环芳烃，也呈现出类似的远距离下风浓度梯度。相比之下，在日出后、上午和下午在同一路线上测量的空气污染物浓度，呈现出如早期研究中所发现的典型白天下风方向浓度在约300米内降至背景水平的情况。尽管高速公路日出前的交通流量远低于白天拥堵高峰，但日出前时段下风方向的UFP浓度显著高于白天；UFP和一氧化氮浓度也与高速公路上的交通流量密切相关。我们将日出前大面积区域内这些升高的浓度与夜间地面温度逆温、低风速和高相对湿度联系起来。在日出前观察到主要道路下风方向存在广泛的空气污染物影响区域，具有重要的暴露评估意义，因为这表明在大多数人在家的日出前时段，道路对居民区有广泛影响。
