Measurement of HONO, HNCO, and Other Inorganic Acids by Negative-Ion Proton-Transfer Chemical-Ionization Mass Spectrometry (NI-PT-CIMS): Application to Biomass Burning Emissions

A negative-ion proton-transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO(3)), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO(3) and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4s, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO(3)center dot NO(3)(-) clusters within the CIMS, and NO(2)-water production on inlet surfaces, and were quite minor (\u3c= 1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume) for a 1 min average. The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, in which both acids were seen to be important products

An odd oxygen framework for wintertime ammonium nitrate aerosol pollution in urban areas: NOx and VOC control as mitigation strategies

Wintertime ammonium nitrate aerosol pollution is a severe air quality issue affecting both developed and rapidly urbanizing regions from Europe to East Asia. In the US, it is acute in western basins subject to inversions that confine pollutants near the surface. Measurements and modeling of a wintertime pollution episode in Salt Lake City, Utah demonstrates that ammonium nitrate is closely related to photochemical ozone through a common parameter, total odd oxygen, Ox,total. We show that the traditional NOx‐VOC framework for evaluating ozone mitigation strategies also applies to ammonium nitrate. Despite being nitrate‐limited, ammonium nitrate aerosol pollution in Salt Lake City is responsive to VOC control and, counterintuitively, not initially responsive to NOx control. We demonstrate simultaneous nitrate limitation and NOx saturation and suggest this phenomenon may be general. This finding may identify an unrecognized control strategy to address a global public health issue in regions with severe winter aerosol pollution

MOR2 ecological data

Those listed as authors substantially designed instruments and data collection protocols, directly supervised data collection and collected data, designed database, and oversaw data entry and quality checkingAdditional acknowledgements (People listed assisted with field data collection, data entry, and establishment of on-line data archive): The following individuals helped with data collection or data entry and consulting: Adyabadam G., Ariunsukh, Ariunzaya, Arren A., Atarbold, Baagii, Bolormaa, Batkhishig B., Bayarmaa B., Brandon B., Bulgamaa, Bulgana U., Byambaa, D., Dejidmaa Ts., Erica C., Enkhjargal, Enkmunkh B., Gandiimaa, Ganjargal, Gankhuyag L., Gantsogt, Itgelt N., Jargal Ya., Jay A., Justin V., Khishigdorj, Khishigjargal B., Lkhagvasuren D., Lkhagvasuren, Lkhamdulam, Narangerel, Naransogt, Niah V., Odgarav J., Oyuntsetseg, Oyunsuvd S., Pagmajav D., Retta B., Sainchuluun A., Sergelen M., Solongo, Sophia L., Sukhbaatar, Sumjidmaa, Tsengelmaa L., Tserendash S., Tsogtbaatar J., Tumee, Turbagana, Undarmaa J., Unurzul A., Urlee, Vandandorj S., Zolzaya, other members of our great field teams, local government officers and supporters. The following individuals guided establishment of on-line data archive at Colorado State University: Tobin Magle, Mara Sedlins, Daniel DraperThe following institutions helped and participated in the project: Nutag Action Research Institute, Institute of Geo-Ecology, Research Institute of Animal Husbandry, Mongolian Society for Range Management, German Technical Cooperation (GTZ) , Institute of Botany, Institute of Meteorology and Hydrology, Institute of Chemistry and Chemical Technology, Mongolian State Agricultural University, Center for Ecosystem Studies, Texas A&M University and Colorado State University.MOR2 ecological data were collected from 143 winter camps at three different grazing distances in four different ecological zones. Ecological field data includes soil pit descriptions, soul surface data including resource retention class and soil redistribution class data; site environmental data (i.e. metadata), and vegetation data including plant biomass by functional group and plant cover by species.The following organizations provided funding for data collection, entry or analysis: National Science Foundation BCS-1011801, The World Bank, US AID, American Association of University Women, Open Society Institute, Center for Collaborative Conservation, Colorado State University

A large and ubiquitous source of atmospheric formic acid

Formic acid (HCOOH) is one of the most abundant acids in the atmosphere, with an important influence on precipitation chemistry and acidity. Here we employ a chemical transport model (GEOS-Chem CTM) to interpret recent airborne and ground-based measurements over the US Southeast in terms of the constraints they provide on HCOOH sources and sinks. Summertime boundary layer concentrations average several parts-per-billion, 2–3× larger than can be explained based on known production and loss pathways. This indicates one or more large missing HCOOH sources, and suggests either a key gap in current understanding of hydrocarbon oxidation or a large, unidentified, direct flux of HCOOH. Model-measurement comparisons implicate biogenic sources (e.g., isoprene oxidation) as the predominant HCOOH source. Resolving the unexplained boundary layer concentrations based (i) solely on isoprene oxidation would require a 3× increase in the model HCOOH yield, or (ii) solely on direct HCOOH emissions would require approximately a 25× increase in its biogenic flux. However, neither of these can explain the high HCOOH amounts seen in anthropogenic air masses and in the free troposphere. The overall indication is of a large biogenic source combined with ubiquitous chemical production of HCOOH across a range of precursors. Laboratory work is needed to better quantify the rates and mechanisms of carboxylic acid production from isoprene and other prevalent organics. Stabilized Criegee intermediates (SCIs) provide a large model source of HCOOH, while acetaldehyde tautomerization accounts for ~ 15% of the simulated global burden. Because carboxylic acids also react with SCIs and catalyze the reverse tautomerization reaction, HCOOH buffers against its own production by both of these pathways. Based on recent laboratory results, reaction between CH₃O₂ and OH could provide a major source of atmospheric HCOOH; however, including this chemistry degrades the model simulation of CH₃OOH and NO_<i>x</i> : CH₃OOH. Developing better constraints on SCI and RO₂ + OH chemistry is a high priority for future work. The model neither captures the large diurnal amplitude in HCOOH seen in surface air, nor its inverted vertical gradient at night. This implies a substantial bias in our current representation of deposition as modulated by boundary layer dynamics, and may indicate an HCOOH sink underestimate and thus an even larger missing source. A more robust treatment of surface deposition is a key need for improving simulations of HCOOH and related trace gases, and our understanding of their budgets