Technical note: Gas-phase nitrate radical generation via irradiation of aerated ceric ammonium nitrate mixtures

<p>We present a novel photolytic source of gas-phase <span class="inline-formula">NO₃</span> suitable for use in atmospheric chemistry studies that has several advantages over traditional sources that utilize <span class="inline-formula">NO₂</span> <span class="inline-formula">+</span> <span class="inline-formula">O₃</span> reactions and/or thermal dissociation of dinitrogen pentoxide (<span class="inline-formula">N₂O₅</span>). The method generates <span class="inline-formula">NO₃</span> via irradiation of aerated aqueous solutions of ceric ammonium nitrate (CAN, <span class="inline-formula">(NH₄)₂Ce(NO₃)₆</span>) and nitric acid (<span class="inline-formula">HNO₃</span>) or sodium nitrate (<span class="inline-formula">NaNO₃</span>). We present experimental and model characterization of the <span class="inline-formula">NO₃</span> formation potential of irradiated CAN <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6bfc4ae3491d603d986b6e1d0e6866cf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-13869-2023-ie00001.svg" width="8pt" height="14pt" src="acp-23-13869-2023-ie00001.png"/></svg:svg></span></span> <span class="inline-formula">HNO₃</span> and CAN <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="539a58614ea8688159b8effbc6d3da8d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-13869-2023-ie00002.svg" width="8pt" height="14pt" src="acp-23-13869-2023-ie00002.png"/></svg:svg></span></span> <span class="inline-formula">NaNO₃</span> mixtures containing [CAN] <span class="inline-formula">=</span> 10<span class="inline-formula">⁻³</span> to 1.0 M, [<span class="inline-formula">HNO₃</span>] <span class="inline-formula">=</span> 1.0 to 6.0 M, [<span class="inline-formula">NaNO₃</span>] <span class="inline-formula">=</span> 1.0 to 4.8 M, photon fluxes (<span class="inline-formula"><i>I</i></span>) ranging from 6.9 <span class="inline-formula">×</span> 10<span class="inline-formula">¹⁴</span> to 1.0 <span class="inline-formula">×</span> 10<span class="inline-formula">¹⁶</span> photons cm<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹</span>, and irradiation wavelengths ranging from 254 to 421 nm. <span class="inline-formula">NO₃</span> mixing ratios ranging from parts per billion to parts per million by volume were achieved using this method. At the CAN solubility limit, maximum [<span class="inline-formula">NO₃</span>] was achieved using [<span class="inline-formula">HNO₃</span>] <span class="inline-formula">≈</span> 3.0 to 6.0 M and UVA radiation (<span class="inline-formula"><i>λ</i>_max⁡</span> <span class="inline-formula">=</span> 369 nm) in CAN <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M35" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="07d7a1dd05fd1823c5d4d7644fe5a26c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-13869-2023-ie00003.svg" width="8pt" height="14pt" src="acp-23-13869-2023-ie00003.png"/></svg:svg></span></span> <span class="inline-formula">HNO₃</span> mixtures or [<span class="inline-formula">NaNO₃</span>] <span class="inline-formula">≥</span> 1.0 M and UVC radiation (<span class="inline-formula"><i>λ</i>_max⁡</span> <span class="inline-formula">=</span> 254 nm) in CAN <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M41" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="dec69c2f61a2c3df83845e73f901bed1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-13869-2023-ie00004.svg" width="8pt" height="14pt" src="acp-23-13869-2023-ie00004.png"/></svg:svg></span></span> <span class="inline-formula">NaNO₃</span> mixtures. Other reactive nitrogen (<span class="inline-formula">NO₂</span>, <span class="inline-formula">N₂O₄</span>, <span class="inline-formula">N₂O₅</span>, <span class="inline-formula">N₂O₆</span>, <span class="inline-formula">HNO₂</span>, <span class="inline-formula">HNO₃</span>, <span class="inline-formula">HNO₄</span>) and reactive oxygen (<span class="inline-formula">HO₂</span>, <span class="inline-formula">H₂O₂</span>) species obtained from the irradiation of ceric nitrate mixtures were measured using a <span class="inline-formula">NO_<i>x</i></span> analyzer and an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). To assess the applicability of the method for studies of <span class="inline-formula">NO₃</span>-initiated oxidative aging processes, we generated and measured the chemical composition of oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) from the <span class="inline-formula"><i>β</i></span>-pinene <span class="inline-formula">+</span> <span class="inline-formula">NO₃</span> reaction using a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to the HR-ToF-CIMS.</p>