Systems and methods for measuring nitrate levels

Abstract

The systems and methods described herein relate to the measurement of nitrate levels in a sample of gas, for example, air, exhaust, or other sources of gas. Moreover, the systems and methods described herein are capable of operating using short sample collection periods, permitting rapid data collection and finely time-resolved nitrate monitoring over a span of time. Additionally, ambient nitrate can effectively be distinguished from other airborne particles, such as sulfate and carbon.

1 . A system for measuring nitrate levels, comprising 
 a sample inlet for receiving a sample of gas,    a collection body coupled to said sample inlet,    a filter mounted within said body to collect particles from said sample of gas,    a heater coupled to the body to heat the body,    a gas inlet coupled to said body to provide a flow of gas through said body, and    a detector coupled to said body to measure an NO x  concentration.    
     
     
         2 . The system of  claim 1 , further comprising 
 a source of gas coupled to said gas inlet.    
     
     
         3 . The system of  claim 2 , wherein said gas is nitrogen.  
     
     
         4 . The system of  claim 2 , wherein said gas is substantially free of oxygen.  
     
     
         5 . The system of  claim 1 , further comprising 
 a catalyst, coupled to said body and to said detector, capable of reducing NO 2  to NO.    
     
     
         6 . The system of  claim 5 , wherein said catalyst comprises molybdenum.  
     
     
         7 . The system of  claim 1 , wherein said detector includes a light sensor.  
     
     
         8 . The system of  claim 7 , wherein said detector further includes an ozone generator.  
     
     
         9 . The system of  claim 1 , wherein said detector includes an infrared sensor.  
     
     
         10 . The system of  claim 1 , wherein said detector includes a material which reversibly binds NO.  
     
     
         11 . The system of  claim 1 , wherein said filter comprises quartz fibers.  
     
     
         12 . The system of  claim 1 , further comprising 
 an extractor coupled to said sample inlet and to said collection body to substantially remove NO 2  from the gas sample.    
     
     
         13 . The system of  claim 12 , wherein the extractor comprises a hydroxyl-bearing solvent and a base.  
     
     
         14 . The system of  claim 13 , wherein the hydroxyl-bearing solvent is glycerol and the base is an organic base.  
     
     
         15 . The system of  claim 14 , wherein the organic base is an amine.  
     
     
         16 . The system of  claim 12 , further comprising 
 a selection platform, situated between said sample inlet and said extractor, to substantially remove particles larger than about 2.5 microns.    
     
     
         17 . The system of  claim 16 , wherein said selection platform is a filter.  
     
     
         18 . The system of  claim 16 , wherein said selection platform is an inertial impactor.  
     
     
         19 . The system of  claim 1 , further comprising 
 a cooling system to cool the collection body.    
     
     
         20 . A method for measuring a level of nitrate, comprising 
 receiving a gas sample,    collecting nitrate particles from the gas sample on a filter,    passing a stream of gas substantially free of oxygen over the collected particles,    volatilizing the collected particles by heating to generate NO x , and    measuring a level of NO x .    
     
     
         21 . The method of  claim 20 , further comprising 
 substantially removing NO 2  prior to collecting nitrate particles.    
     
     
         22 . The method of  claim 21 , wherein substantially removing NO 2  includes passing the received sample over a hydroxyl-bearing solvent and a base.  
     
     
         23 . The method of  claim 21 , wherein substantially removing NO 2  includes passing the received sample over a hydroxyl-bearing solvent and an organic base.  
     
     
         24 . The method of  claim 21 , wherein substantially removing NO 2  includes passing the received sample over a mixture comprising glycerol and triethanolamine.  
     
     
         25 . The method of  claim 20 , further comprising 
 removing particles larger than about  2 . 5  microns from the received gas sample.    
     
     
         26 . The method of  claim 25 , wherein substantially removing particles larger than about 2.5 microns includes passing the received sample through an inertial impactor.  
     
     
         27 . The method of  claim 25 , wherein substantially removing particles larger than about 2.5 microns includes passing the received sample through a filter.  
     
     
         28 . The method of  claim 20 , wherein passing a stream of gas includes passing a stream of nitrogen over the collected particles.  
     
     
         29 . The method of  claim 20 , further comprising 
 reducing generated NO 2  to NO using a metal catalyst.    
     
     
         30 . The method of  claim 29 , wherein reducing generated NO 2  includes contacting said NO 2  with a molybdenum catalyst.  
     
     
         31 . The method of  claim 20 , wherein measuring a level of NO x  includes reacting NO with ozone.  
     
     
         32 . The method of  claim 20 , wherein measuring a level of NO x  includes detecting infrared absorption.  
     
     
         33 . The method of  claim 20 , wherein measuring a level of NO x  includes adsorbing NO x  on a conductive material.  
     
     
         34 . The method of  claim 20 , wherein collecting nitrate particles comprises collecting nitrate particles on a filter comprising quartz fibers.  
     
     
         35 . The method of  claim 20 , wherein volatilizing the collected particles includes rapidly heating the collected particles to at least 300° C.  
     
     
         36 . A system for measuring nitrate levels, comprising 
 a sample inlet to receive a sample of gas,    an extractor coupled to said sample inlet to substantially remove NO 2  from the gas sample,    a collection body coupled to said sample inlet,    an inertial impactor mounted within said body to collect particles from the gas sample,    a current source coupled to the inertial impactor to heat the inertial impactor and generate NO x , and    a detector coupled to said catalyst to measure an NO x  concentration.    
     
     
         37 . A method for measuring a level of nitrate, comprising 
 receiving a gas sample,    substantially removing NO 2  from the gas sample,    collecting nitrate particles from the gas sample with an inertial impactor,    passing a stream of gas substantially free of oxygen over the collected particles,    volatilizing the collected particles by heating to generate NO x , and    measuring a level of NO, generated by the heated particles.    
     
     
         38 . A system for measuring nitrate levels, comprising 
 means for receiving a sample of gas,    support means coupled to said means for receiving,    means for collecting particles coupled to said support means,    means, coupled to said support means, for heating the support means to generate NO x ,    means, coupled to said support means, for flowing a stream of gas through said support means, and    means for measuring an NO x  concentration coupled to said support means.    
     
     
         39 . The system of  claim 38 , further comprising 
 means for substantially removing NO 2  from the sample of gas, coupled to said means for receiving and said support means.    
     
     
         40 . The system of  claim 38 , further comprising 
 means for reducing NO 2  to NO, coupled to said support means and to said means for measuring.    
     
     
         41 . A method of manufacturing a nitrate measurement apparatus, comprising 
 providing a sample inlet for receiving a sample of gas,    coupling a collection body to said sample inlet,    disposing a filter within said body,    coupling a heater to the body,    coupling a gas inlet to said body, and    coupling an NO x  detector to said body.    
     
     
         42 . The method of  claim 41 , further comprising 
 disposing an NO 2  extractor between said sample inlet and said collection body.    
     
     
         43 . The method of  claim 41 , further comprising 
 disposing a catalyst capable of reducing NO 2  to NO between said collection body and said NO x  detector.