delta NO3 (ug/m3)= 745.7/TR* 1/24* E (Ki

½) [5.2]

i=1

where delta NO3 is the amount of volatilized nitrate mass, TR is the reference temperature for the

sampled air volume in degrees Kelvin and Ki is the dissociation constant for ammonium nitrate

evaluated at the ambient temperature for hour i. The nitrate loss can be predicted for each day,

based on hourly temperature and relative humidity data. The SMAT analysis for CAIR used

National Weather Service temperature and relative humidity data for the closest station. Other

sources of meteorological data may also be appropriate. Further details on the nitrate loss

calculations can be found in (Frank, 2006).

Ammonium Associated with Sulfates and Retained Nitrates

To determine the mass associated with nitrates, we first assume retained nitrate is

probably all ammonium nitrate. Thus the ammonium associated with nitrates can be derived

directly from the measured or predicted NO3FRM as

NH4NO3 = 0.29 * NO3FRM [5.3]

The difference between total FRM NH4 (amount associated with nitrates and sulfates),

termed NH4FRM, and the measured NH4, termed NH4STN,, is needed to determine the ammoniated

form of sulfates as described by equation 5.1. Recent measurement study by Collett (Collett,

2004) shows that NH4 may not be completely retained during collection on nylon filters

preceded by a nitric acid denuder. During sampling conditions associated with nitrate

volatilization, ammonium nitrate dissociates but the HNO3 downstream of the denuder is

recaptured on the basic nylon media and the result is reported as particle nitrate. On the other

hand, the NH4+ volatilizes to gaseous NH3 and apparently passes thru the filter. At several FRM

 

n601 - n602 - n603 - n604 - n605 - n606 - n607 - n608 - n609 - n610 - n611 - n612 - n613 - n614 - n615 - n616 - n617 - n618 - n619 - n620 - n621 - n622 - n623 - n624 - n625 - n626 - n627 - n628 - n629 - n630 - n631 - n632 - n633 - n634 - n635 - n636 - n637 - n638 - n639 - n640 - n641 - n642 - n643 - n644 - n645 - n646 - n647 - n648 - n649 - n650

 

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