The conditional of an if statement can only check one value at a time, yet deletedValues is a vector. For your if statement to work in the code you've written, you'd need to check one value at a time doing something like this.
if DeleteValues(Vec)
...
However, you don't need a for loop at all. Take advantage of MATLAB's ability to work with vectors.
A = [20.0872
16.1710
20.6179
17.9930
18.6397
16.5852
22.5673
21.0629
19.8378
19.9037
20.2171
21.6581
21.2016
"NoValue"
"NoValue"
"NoValue"
"NoValue"
"NoValue"
"NoValue"
"NoValue"
"NoValue"
"NoValue"];
z = "NoValue";
DeleteValues = strcmp(A,z);
Absorption = A(~DeleteValues)
