Atmospheric Aerosol

:: Section 6

Chemical Composition of Atmospheric Aerosol

The chemical composition of fine and coarse particles in the atmosphere differ greatly. Because there is little mass transfer between the fine and coarse particles, they exist together in the atmosphere as two chemically distinct aerosols. As a group, the fine particles are acidic and contain most of the sulfates, ammonium compounds, hydrocarbons, elemental carbon (soot), toxic metals, and water in the atmosphere. Sulfates and nitrates are the major compositions of cloud condensation nuclei. Carbon (soot) can absorb light and thus have a negative impact on visibility. The coarse particles are basic and contain most of the crustal materials and their oxides, such as silicon, iron, calcium, and aluminum, as well as large sea salt particles and vegetation debris. Table 3 lists the chemical composition of fine and coarse particles.

TABLE 3. Average composition of fine and coarse particles in µg/m³ at an urban and a rural site

	Urban		Rural
	Fine	Coarse	Fine	Coarse
Total Mass	42	27	24	5.6
SO₄^-	17	1.1	12	__
NO₃^-	0.25	1.8	0.3	__
NH₄⁺	4.3	<0.19	2.3	__
H⁺	0.067	<0.01	0.114	__
C	7.6	3.3	3.3	1.3
Al	0.095	1.4	0.02	0.2
Si	0.2	3.8	0.038	0.58
S	__	__	3.7	0.2
Ca	0.15	3.1	0.016	0.32
Fe	0.17	0.73	0.028	0.12
Pb	0.48	0.13	0.097	0.014
Data from Finlayson-Pitts and Pitts, Atmospheric Chemistry: Fundamentals and Experimental Techniques, Wiley, New York, 1986.

	1. What are the three major components of fine aerosols?
	2. What are the four major components of coarse aerosols?

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