Contribution of particulate nitrate to airborne measurements of total reactive nitrogen

Y Miyazaki,Y Kondo,F L Eisele,R J Weber,V N Kapustin,M Koike,N Takegawa,A D Clarke,B Liley,M Zondlo,M Fukuda,Y Ma,D R Blake,A J Weinheimer,K Kita,F Flocke

doi:10.1029/2004jd005502

Abstract

Simultaneous measurements of speciated, total reactive nitrogen (NOy) and particulate NO3− (particle diameter <1.3 μm) were made on board the NASA P‐3B aircraft over the western Pacific in February–April 2001 during the Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment. Gas‐phase and particulate NOy was measured using a gold tube catalytic converter. For the interpretation of particulate NOy, conversion efficiencies of particulate NH4NO3, KNO3, NaNO3, and Ca(NO3)2 were measured in the laboratory. Only NH4NO3 showed quantitative conversion, and its conversion efficiency was as high as that for HNO3. NOy measured on board the aircraft was found to be systematically higher by 10–30% than the sum of the individual NOy gas components (∑(NOy)i) at 0–4 km. Particulate NO3− concentrations measured by a particle‐into‐liquid sampler (PILS) were nearly equal to NOy − ∑(NOy)i under low‐dust‐loading conditions. The PILS data showed that the majority of the particulate NO3− was in the form of NH4NO3 under these conditions, suggesting that NH4NO3 particles were quantitatively converted to detectable NO by the NOy converter, consistent with the laboratory experiments. The contribution of particulate NO3− to NOy was most important at 0–2 km, where NO3− constituted 10–30% of NOy during TRACE‐P. On average, the amounts of particulate NO3− and gas‐phase HNO3 were comparable in this region.

Highlights

NH4NO3 under these conditions, suggesting that NH4NO3 particles were quantitatively converted to detectable NO by the NOy converter, consistent with the laboratory experiments
When we use the NO3À data obtained by the DC-8 filter samples, which measured particles with Dp up to 6 mm [Dibb et al, 2002], particulate NO3À constituted 54% of the total nitrate on average, reaching a maximum of 72% at 0 –2 km where observed particles were heavily influenced by dust during TRACE-P [Jordan et al, 2003b]
In addition to the field measurements, conversion efficiencies of particulate NH4NO3, KNO3, NaNO3, and Ca(NO3)2 by the gold tube catalytic converter were measured in the laboratory

Summary

Introduction

[2] Reactive nitrogen species play a central role in determining the levels of ozone and hydroxyl radicals in the troposphere [e.g., Crutzen, 1979; Liu et al, 1987; Chameides et al, 1992]. One of the major uncertainties in evaluating the budget of reactive nitrogen is due to a lack of fast response and accurate measurements of both gas-phase HNO3 and particulate NO3À. The major uncertainties are (1) particle collection efficiency of the rearward facing inlet and (2) conversion efficiency of particulate NO3À in the NOy converter. NOy measured through forward facing inlets represents amplified particulate NOy plus gas-phase NOy. Fahey et al [2001] observed large, HNO3-containing particles with Dp = 10 – 20 mm in the winter Arctic lower stratosphere by in situ aircraft measurements of NOy. NOy contained in cirrus cloud ice particles has been measured in the upper. The NOy measured through the forward facing inlet (NOy (f)) represents the sum of gas-phase NOy and amplified particulate NO3À. EF represents the enhancement factor for the forward facing inlet, which depends on the size of the particles due to subisokinetic sampling [Fahey et al, 1989]

Laboratory Experiments

Chemical Form of Particulate NOÀ3

Findings

Conclusions