HW4-solution - HOMEWORK 4 (DUE 04/03 @ noon at TAs office)...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
HOMEWORK 4 (DUE 04/03 @ noon at TA’s office) 1. Detection of certain gases can be based on their abilities of absorbing infrared or ultraviolet light at certain wavelengths. List two criteria gaseous pollutants that can apply such detection principle and briefly explain the methods. List one type of measurement interference that would occur applying this detection principle. (10%) SO 2 – absorption of infrared by SO 2 in the air is proportional to SO 2 concentration (FTIR spectrometry). CO – absorption of infrared by CO. Difference of infrared energy in a sample cell and a reference cell is proportional to CO concentration O 3 – absorption of UV light at 254 nm. The reduction of UV energy in the detection cell is proportional to O 3 concentration. The measurement interference would occur when other gases in the sample can absorb light at the same wavelength. For example, certain hydrocarbons may interfere with O3 measurement using a UV photometer because they can absorb UV light at 254 nm to some extent. 2. Explain how a Dichotomous sampler can measure both coarse (PM 2.5-10 ) and fine (PM 2.5 ) particles. (8%) A Dichotomous sampler has a size selective inlet where only particles less than 10 µm (PM 10 ) can enter the sampler. Inside the sampler, larger particles with sufficient inertia are carried by a minor air flow (with a small flow rate) onto a filter. Smaller particles have smaller inertia. They are carried radially away by a major air flow (with a large flow rate) and are collected on another downstream filter. Thus, in a Dichotomous sampler, particles larger than and smaller than a certain size are collected on different filters. By adjusting the flow rates of the minor and major flows, Dichotomous sampler can be used to measure particles greater than 2.5 µm (PM 2.5-10 ) and smaller than 2.5 µm (PM 2.5 ). 3. Q 7.14 Describe differences between accuracy and precision. How is each determined? Accuracy describes how close a measured value is to the true value; precision describes the relative reproducibility of results of multiple measurements of the same concentration. Because these concepts are closely related, accuracy/precision values are commonly expressed together as +/- % values. Q 7.16
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/11/2011 for the course ENV 4101 taught by Professor Wu during the Spring '08 term at University of Florida.

Page1 / 8

HW4-solution - HOMEWORK 4 (DUE 04/03 @ noon at TAs office)...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online