Molar absorptivities (log10) for aqueous nitrate as a function of temperature.
Conversion to cm2/molecule 
sigma = 1000 x ln(10) x (molar abs., 1/M) = 3.82e-21 x (molar abs)
From Chu and Anastasio, Quantum yields of hydroxyl radical and nitrogen 
dioxide from the photolysis of nitrate on ice, J. Phys. Chem. A, 107, 
9594-9602, 2003. (table 2 from Supplemental Information)
nm  278K 283K 288K 293K 298K 
280 3.70 3.64 3.60 3.55 3.54 
282 4.12 4.06 4.02 3.94 3.93 
284 4.55 4.49 4.45 4.38 4.36 
286 4.97 4.91 4.85 4.79 4.77 
288 5.38 5.33 5.28 5.20 5.17 
290 5.81 5.73 5.68 5.59 5.57 
292 6.21 6.14 6.07 6.01 5.97 
294 6.57 6.50 6.44 6.36 6.32 
296 6.87 6.81 6.75 6.66 6.64 
298 7.10 7.03 6.98 6.91 6.89 
300 7.21 7.16 7.12 7.05 7.02 
301 7.23 7.19 7.16 7.08 7.05 
302 7.22 7.18 7.15 7.08 7.06 
304 7.10 7.08 7.05 6.99 6.98 
306 6.87 6.86 6.86 6.80 6.78 
308 6.57 6.54 6.54 6.49 6.49 
310 6.13 6.11 6.12 6.10 6.11 
312 5.58 5.61 5.63 5.60 5.61 
313 5.29 5.32 5.34 5.33 5.33 
314 4.99 5.01 5.05 5.04 5.06 
316 4.36 4.38 4.41 4.41 4.44 
318 3.70 3.73 3.76 3.78 3.80 
320 3.08 3.11 3.15 3.16 3.19 
322 2.49 2.53 2.57 2.58 2.62 
324 1.97 2.00 2.03 2.07 2.10 
326 1.50 1.53 1.58 1.59 1.62 
328 1.10 1.13 1.17 1.18 1.22 
330 0.776 0.804 0.829 0.855 0.870 
332 0.538 0.561 0.584 0.591 0.616 
334 0.373 0.391 0.409 0.406 0.424 
336 0.260 0.262 0.282 0.281 0.296 
338 0.164 0.179 0.187 0.189 0.205 
340 0.129 0.130 0.140 0.130 0.139 
342 0.086 0.086 0.098 0.088 0.098 
344 0.062 0.071 0.068 0.069 0.071 
346 0.044 0.039 0.047 0.048 0.048 
348 0.028 0.031 0.031 0.029 0.031 
350 0.017 0.018 0.016 0.018 0.018 
352 0.008 0.010 0.011 0.009 0.010 
354 0.005 0.005 0.005 0.005 0.005 
356 0.003 0.003 0.003 0.003 0.003 
358 0.001 0.001 0.001 0.001 0.001 
360 0.000 0.000 0.000 0.000 0.000