Bình phun An là một hệ thống các hạt nhỏ lơ lửng trong khí. Bình xịt hoặc các hạt vật chất tham khảo bất kỳ chất nào, ngoại trừ nước tinh khiết, tồn tại như một chất lỏng hoặc chất rắn trong bầu khí quyển trong điều kiện bình thường và có kích thước hiển vi hoặc submicroscopic nhưng lớn hơn kích thước phân tử. Có hai cơ chế cơ bản khác nhau của sự hình thành khí dung: • • mầm từ các phân tử hơi (quang, đốt, .) nghiền của vật chất rắn hoặc lỏng (mài, xói mòn,. | AEROSOLS An aerosol is a system of tiny particles suspended in a gas. Aerosols or particulate matter refer to any substance except pure water that exists as a liquid or solid in the atmosphere under normal conditions and is of microscopic or submicrosco-pic size but larger than molecular dimensions. There are two fundamentally different mechanisms of aerosol formation nucleation from vapor molecules photochemistry combustion etc. comminution of solid or liquid matter grinding erosion sea spray etc. Formation by molecular nucleation produces particles of diameter smaller than mm. Particles formed by mechanical means tend to be much larger diameters exceeding 10 mm or so and tend to settle quickly out of the atmosphere. The very small particles formed by nucleation due to their large number tend to coagulate rapidly to form larger particles. Surface tension practically limits the smallest size of particles that can be formed by mechanical means to about 1 mm. PARTICLE SIZE DISTRIBUTION Size is the most important single characterization of an aerosol particle. For a spherical particle diameter is the usual reported dimension. When a particle is not spherical the size can be reported either in terms of a length scale characteristic of its silhouette or of a hypothetical sphere with equivalent dynamic properties such as settling velocity in air. Table 1 summarizes the physical interpretation for a variety of characteristic diameters. The Feret and Martin diameters are typical geometric diameters obtained from particle silhouettes under a microscope. TABLE 1 Measures of particle size Definition of characteristic diameters Physical meaning and corresponding measuring method geometric size b Ỉ 2 b Ỉ 1 3 bỈt 1 3 3 1 Ỉ 1 b 1 t V b 2Ỉb 2bt 2Ỉt 6 equivalent diam. breadth b length Ỉ Feret diam. Martin diam. equivalent projection area diam. Heywood diam. equivalent surface area diam. specific surface diam. s p 1 2 equivalent volume diam. 6v p 1 3 Stokes diam. 15 .
