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Diurnal and seasonal characteristics of particle volatility and chemical composition in the vicinity of a light-duty vehicle freeway

机译：轻型汽车高速公路附近颗粒挥发性和化学成分的昼夜变化

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During the winter of 2005, physicochemical properties of size-fractionated PM_(10) particles were analyzed next to State Route 110 (Pasadena freeway in Los Angeles, CA, USA), a light-duty vehicle freeway, closed to heavy-duty traffic. We report volatility of ultrafine particles and chemical characteristics in the coarse, accumulation, and ultrafine modes very close to the freeway and at an urban background site. For measurement of mass and chemical composition, the study employed in each location a Micro-Orifice Uniform Deposit Impactor (MOUDI) and a modified high-volume sampler. Both instruments sampled with the same size cutpoints. A tandem differential mobility analyzer (TDMA) was used at the two sampling sites to analyze the semivolatile fraction of the aerosols. Size distributions of the ambient aerosol were measured using a DMA and total number concentration using a condensation particle counter (CPC). In this study, which was a continuation of a campaign during summer 2004, we compared the seasonal, i.e. winter versus summer, and diurnal, i.e. daytime versus evening, variation in PM characteristics in the vicinity of this freeway. Conditions in winter differed most from those in summer during the evening rush-hour traffic, with much lower temperatures in the winter campaign. Diurnal variations in particle volatility were observed, with higher content of volatile material in aerosols sampled in the evenings. Particle number concentrations were also much higher during the evening hours, increasing from 67,000 to 110,000 cm~(-3). The average total number concentration next to the freeway was 80,000 cm~(-3) during the sampling period, which was higher than in summer, when the average was 46,000cm~(-3). External mixing was observed with increasing nonvolatile fractions for 40, 80, and 120nm particles (39% of particles). In general the volatility increased in the evenings, while the nonvolatile fraction decreased.
机译：在2005年冬季，对110号州际公路（美国加利福尼亚州洛杉矶的帕萨迪纳高速公路），轻型车辆高速公路，禁止重载的高速公路旁进行了大小分级PM_（10）颗粒的理化性质分析。我们报告了非常细的颗粒的挥发性和化学特征，这些特征在非常接近高速公路和城市背景的粗，累积和超细模式下发生。为了测量质量和化学成分，研究在每个位置都使用了微型离心均匀沉积撞击器（MOUDI）和改进的大容量采样器。两种仪器都以相同大小的切点采样。在两个采样点使用串联差动迁移率分析仪（TDMA）分析气溶胶的半挥发性成分。使用DMA测量环境气溶胶的尺寸分布，使用冷凝粒子计数器（CPC）测量总浓度。在这项研究（这是2004年夏季运动的延续）中，我们比较了该高速公路附近PM特征的季节性变化（即冬季与夏季之间的差异）和昼夜变化（即白天与晚上之间）的差异。在晚上的高峰时段，冬季的状况与夏季的状况差异最大，冬季运动的温度要低得多。观察到颗粒挥发性的昼夜变化，晚上采样的气溶胶中挥发性物质含量更高。傍晚时分，颗粒数浓度也更高，从67,000 cm〜（-3）增加到110,000 cm〜（-3）。采样期间，高速公路旁的平均总浓度为80,000 cm〜（-3），高于夏季的平均值，平均值为46,000cm〜（-3）。对于40、80和120nm的颗粒（占颗粒的39％），观察到外部混合的非挥发性组分增加。一般而言，晚上的挥发性增加，而非挥发性成分减少。

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