Monica Martinez - Academia.edu (original) (raw)

Papers by Monica Martinez

J Atmos Chem, 2004

Accurate OH and HO 2 (collectively called HO x ) measurements by laser-induced fluorescence (LIF)... more Accurate OH and HO 2 (collectively called HO x ) measurements by laser-induced fluorescence (LIF) may be contaminated by spurious signals from interfering atmospheric chemicals or from the instrument itself. Interference tests must be conducted to ensure that observed OH signal originates solely from ambient OH and is not due to instrument artifacts. Several tests were performed on the Penn State LIF HO x instrument, both in the laboratory and in the field. These included measurements of the instrument's zero signal by using either zero air or perfluoropropylene to remove OH, examination of spectral interferences from naphthalene, sulfur dioxide, and formaldehyde, and tests of interferences by addition of suspected interfering atmospheric chemicals, including ozone, hydrogen peroxide, nitrous acid, formaldehyde, nitric acid, acetone, and organic peroxy radicals (RO 2 ). All tests lacked evidence of significant interferences for measurements in the atmosphere, including highly polluted urban environments.

Hydroxyl (OH) and hydroperoxyl (HO2) radicals (collectively called HOx) were measured by A laser-... more Hydroxyl (OH) and hydroperoxyl (HO2) radicals (collectively called HOx) were measured by A laser-induced fluorescence (LIF) instrument during the PM2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY) summer 2001 intensive campaign in New York City. Measurement results for about one month were presented. Diurnal cycles of OH and HO2 show that the daytime maximum concentrations were 0.2-0.8 pptv and 2-22 pptv, respectively. Relatively high OH and HO2 persisted into early evening and were frequently observed during nighttime. This observation suggests that HOx chemistry may play an important role in the nighttime oxidation processes in the polluted urban atmosphere. The observed OH and HO2 concentrations were compared with those calculated by a box model that used RACM and was constrained to the ancillary measurements. For HO2, the observed concentration levels and variations were usually well reproduced by the model calculations, with a model to observation ratio of 0.85 on average for day and night. For OH, the model was generally able to match the measurement during daytime with a model to observation ratio of about 0.89, while the calculations significantly underestimated OH during nighttime. The budgets of HOx show that primary HOx production was dominated by the photolysis of HONO during daytime due to relatively high HONO concentrations, while nighttime HOx were primarily from the O3 and NO3 reactions with alkenes. The OH reactivity measurements agreed well with the calculations for both composite diurnal variation and individual days. Calculations indicate that the reactions of OH + NO2, OH + hydrocarbons, OH + CO, and OH + NO accounted for about 32%, 25%, 12% and 10% of total OH loss, respectively, in this urban area.

Reactions with radicals are the main self-cleansing mechanism of the atmosphere. A wide range of ... more Reactions with radicals are the main self-cleansing mechanism of the atmosphere. A wide range of chemical compounds emitted by human activities such as industrial processes and traffic, and also by vegetation and animals, are oxidised by reactions with radicals, ultimately leading to their removal from the atmosphere. The most reactive radical is OH, which is photochemically produced in the atmosphere. The aim of the HOOVER (HOx Over Europe) campaigns was to study the seasonal and latitudinal dependencies of radical photochemistry in the free troposphere over Europe, with flights from Germany to northern Europe (Kiruna, 67°N) and to southern Europe (Sardinia, 39°N). Two HOOVER campaigns have been undertaken, an autumn campaign which took place in October 2006 and a summer campaign in July 2007. Here we present data for OH and HO2 collected during the HOOVER campaigns, supplemented with other trace gas measurements, and compare them with simulated OH and HO2 from a constrained box mo...

ABSTRACT OH is the major oxidant in the troposphere. While in polluted air masses it is involved ... more ABSTRACT OH is the major oxidant in the troposphere. While in polluted air masses it is involved in the removal of pollutants and the formation of ozone and aerosols, in unpolluted air it removes ozone. As OH is in a fast steady state with HO2, the sum of both is commonly addressed as HOx. We present OH and HO2 data from the DC8 during the Trace-P mission, which was focused on assessing the emissions from East Asia and study their chemical evolution into the pacific basin. During Trace-P a broad spectrum of conditions was observed. The changing photolysis frequencies during sunrise and sunsets can be used to test our understanding of photolytic HOx sources. We show how HOx evolves in the moderately polluted marine boundary layer and the clean free troposphere during sunrise. We also present the observed in situ O3 budget at different locations and altitudes and study the effects of aerosols on HOx during cloud and dust events.

Atmospheric Chemistry and Physics Discussions, 2012

We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemi... more We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model (MXLCH) coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO campaign , numerical experiments are performed to study 5 the role of ABL dynamics and the accuracy of chemical schemes with different complexity: MOZART-4 and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O 3 -NO x -VOC-HO x diurnal cycle during conditions characterised by a low NO x regime and small O 3 tendencies (less than 1 ppb per hour). By focussing on 10 the budget equations of chemical species in the mixed-layer model, we show that for species like O 3 , NO and NO 2 , the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the daily cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing 15 time scale of turbulence, we propose a classification based on the Damköhler number to further determine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement 20 campaigns.

Atmospheric Measurement Techniques Discussions, 2014

ABSTRACT Ambient measurements of hydroxyl radicals (OH) are challenging due to a high reactivity ... more ABSTRACT Ambient measurements of hydroxyl radicals (OH) are challenging due to a high reactivity and consequently low concentration. The importance of OH as an atmospheric oxidant has resulted in a sustained effort leading to the development of a number of analytical techniques. Recent work has indicated that the laser-induced fluorescence of the OH molecules method based on the fluorescence assay by gas expansion technique (LIF-FAGE) for the measurement of atmospheric OH in some environments may be influenced by artificial OH generated within the instrument, and a chemical method to remove this interference was implemented in a LIF-FAGE system by Mao et al. (2012). We have applied this method to our LIF-FAGE HORUS (HydrOxyl Radical Measurement Unit based on fluorescence Spectroscopy) system, and developed and deployed an inlet pre-injector (IPI) to determine the chemical zero level in the instrument via scavenging the ambient OH radical. We describe and characterise this technique in addition to its application at field sites in forested locations in Finland, Spain, and Germany. Ambient measurements show that OH generated within the HORUS instrument is a non-negligible fraction of the total OH signal, which can comprise 30% to 80% during the day and 60% to 100% during the night. The contribution of the background OH varied greatly between measurement sites and was likely related to the type and concentration of volatile organic compounds (VOCs) present at each particular location. Two inter-comparisons in contrasting environments between the HORUS instrument and two different chemical ionisation mass spectrometers (CIMS) are described to demonstrate the efficacy of the inlet-pre-injector and the necessity of the chemical zeroing method in such environments.

Atmospheric Chemistry and Physics, 2013

In situ airborne measurements of OH and HO 2 with the HORUS (HydrOxyl Radical measurement Unit ba... more In situ airborne measurements of OH and HO 2 with the HORUS (HydrOxyl Radical measurement Unit based on fluorescence Spectroscopy) instrument were performed in the summertime upper troposphere across Europe during the HOOVER 2 (HO x OVer EuRope) campaign in July 2007. Complementary measurements of trace gas species and photolysis frequencies were conducted to obtain a broad data set, which has been used to quantify the significant HO x sources and sinks. In this study we compare the in situ measurement of OH and HO 2 with simulated mixing ratios from the constrained box model CAABA/MECCA (Chemistry As A Box Model Application/Module Efficiently Calculating the Chemistry of the Atmosphere), and the global circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry Model). The constrained box model reproduces the observed OH and HO 2 mixing ratios with better agreement (obs/mod median 98 % OH, 96 % HO 2 ) than the global model (median 76 % OH, 59 % HO 2 ). The observations and the computed HO x sources and sinks are used to identify deviations between the models and their impacts on the calculated HO x budget.

Science, 2004

36. We thank J. Smith and B. Toon for raising questions about the relative importance of boundary... more 36. We thank J. Smith and B. Toon for raising questions about the relative importance of boundary-layer and free tropospheric aerosols, E. Zipser for sharing his experience with tropical convection, W. McKie for keeping our more than 70 computer processors running in concert from Key West to Mountain View, and D. Anderson for leading CRYSTAL-FACE with long-term vision.

Journal of Atmospheric Chemistry, 2000

Measurement capability for the detection of atmospheric OH and HO 2 has been developed at the Pen... more Measurement capability for the detection of atmospheric OH and HO 2 has been developed at the Pennsylvania State University over the last decade. The instrument is used in two forms: an aircraft configuration, Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS), and the configuration used on towers, Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS). The instrument uses ultraviolet laser induced fluorescence (LIF) to detect OH in air that is pulled by a vacuum pump through a small inlet into a low-pressure detection chamber; HO 2 is detected by reacting it with NO to form OH, which is detected by LIF in a second detection chamber. In the calibration, equal amounts of OH and HO 2 ranging from 0.15 pptv to 100 pptv are produced via photolysis of water vapor by the 185 nm emission from a low-pressure Hg lamp. Estimated absolute uncertainty at the 2σ confidence level is ±32% for both OH and HO 2 . The dependence of the instrument detection sensitivity has been quantified for changes in ambient water vapor, pressure, laser power, and the flow velocity of ambient air past the inlet. During the last 7 years, the instrument has been deployed in multi-investigator intensive field studies 5 times on the NASA DC-8 aircraft and 8 times on groundbased towers. The descriptions in this manuscript detail our cumulative wisdom of the instrumental response and calibration techniques developed over this time.

Atmospheric Environment, 2003

Observed hydroxyl (OH) and hydroperoxy (HO 2 ) radicals, collectively called HO x , were compared... more Observed hydroxyl (OH) and hydroperoxy (HO 2 ) radicals, collectively called HO x , were compared with OH and HO 2 calculated by a box model that used the regional atmospheric chemistry mechanism and was constrained to the ancillary measurements during the PM 2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY) summer 2001 intensive in New York City. The measurements are described in the companion paper, Ren et al.

Atmospheric Environment, 2003

Hydroxyl (OH) and hydroperoxy (HO 2 ) radicals (collectively called HO x ) were measured by a las... more Hydroxyl (OH) and hydroperoxy (HO 2 ) radicals (collectively called HO x ) were measured by a laser-induced fluorescence instrument during the PMTACS-NY (PM2.5 Technology Assessment and Characterization Study-New York) intensive campaign in New York City in summer 2001. Measurement results for OH and HO 2 are presented for the month-long study. The detection limits were about 3.0 Â 10 5 cm À3 for OH and 2.5 Â 10 6 cm À3 (B0.1 ppt) for HO 2 with a 1-min integration time and a 2s confidence level. The daytime maximum concentrations were 5-20 Â 10 6 cm À3 for OH and 0.4-6 Â 10 8 cm À3 (2-24 pptv) for HO 2 , usually appearing later than the peak of ozone photolysis frequency, J(O 1 D). Relative high OH and HO 2 persisted into early evening and were frequently observed during nighttime. The ratios of HO 2 to OH were typically between 5 and 40, which are smaller than those obtained in relatively clean environments. The OH reactivity, measured by an instrument named total OH loss rate measurement was on average 1973 s À1 in this urban environment. It was the highest in the morning and the lowest in the afternoon. The comparison of measured OH and HO 2 with model calculations is given in a companion paper (OH and HO 2 chemistry in the urban atmosphere of New York City, Atmospheric Environment (2003a) this issue).

Atmospheric Environment, 2010

Both similarities and differences in summertime atmospheric photochemical oxidation appear in the... more Both similarities and differences in summertime atmospheric photochemical oxidation appear in the comparison of four field studies: ). The compared photochemical indicators are OH and HO 2 abundances, OH reactivity (the inverse of the OH lifetime), HO x budget, OH chain length (ratio of OH cycling to OH loss), calculated ozone production, and ozone sensitivity. In terms of photochemical activity, Houston is much more like Mexico City than New York City. These relationships result from the ratio of volatile organic compounds (VOCs) to nitrogen oxides (NO x ), which are comparable in Houston and Mexico City, but much lower in New York City. Compared to New York City, Houston and Mexico City also have higher levels of OH and HO 2 , longer OH chain lengths, a smaller contribution of reactions with NO x to the OH reactivity, and NO x -sensitivity for ozone production during the day. In all four studies, the photolysis of nitrous acid (HONO) and formaldehyde (HCHO) are significant, if not dominant, HO x sources. A problematic result in all four studies is the greater OH production than OH loss during morning rush hour, even though OH production and loss are expected to always be in balance because of the short OH lifetime. The cause of this discrepancy is not understood, but may be related to the underpredicted HO 2 in high NO x conditions, which could have implications for ozone production. Three photochemical indicators show particularly high photochemical activity in Houston during the TRAMP2006 study: the long portion of the day for which ozone production was NO x -sensitive, the calculated ozone production rate that was second only to Mexico City's, and the OH chain length that was twice that of any other location. These results on photochemical activity provide additional support for regulatory actions to reduce reactive VOCs in Houston in order to reduce ozone and other pollutants.

Atmospheric Chemistry and Physics, 2011

In this study we report measurements of hydrogen peroxide (H 2 O 2 ), methyl hydroperoxide* (MHP*... more In this study we report measurements of hydrogen peroxide (H 2 O 2 ), methyl hydroperoxide* (MHP* as a proxy of MHP based on an unspecific measurement of total organic peroxides) and formaldehyde (HCHO) from the HO x OVer EuRope (HOOVER) project (HO x = OH+HO 2 ). HOOVER included two airborne field campaigns, in October 2006 and July 2007. Measurement flights were conducted from the base of operation Hohn (Germany, 54 • N, 9 • E) towards the Mediterranean and to the subpolar regions over Norway. We find negative concentration gradients with increasing latitude throughout the troposphere for H 2 O 2 and CH 3 OOH * . In contrast, observed HCHO is almost homogeneously distributed over central and northern Europe and is elevated over the Mediterranean. In general, the measured gradients tend to be steepest entering the Mediterranean region, where we also find the highest abundances of the 3 species. Mixing ratios of these tracers generally decrease with altitude. H 2 O 2 and CH 3 OOH * show maxima above the boundary layer at 2-5 km, being more distinct over southern than over northern Europe.

Atmospheric Chemistry and Physics, 2012

We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemi... more We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO (Diel Oxidant Mechanisms in relation to Nitrogen Oxides) campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O 3 -NO x -VOC-HO x diurnal cycle during conditions characterized by a low NO x regime and small O 3 tendencies (less than 1 ppb per hour). By focusing on the budget equations of chemical species in the mixedlayer model, we show that for species like O 3 , NO and NO 2 , the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the diel cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further deter-mine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

Atmospheric Chemistry and Physics, 2011

Atmospheric Chemistry and Physics, 2007

We present a comparison of different Lagrangian and chemical box model calculations with measurem... more We present a comparison of different Lagrangian and chemical box model calculations with measurement data obtained during the GABRIEL campaign over the tropical Atlantic Ocean and the Amazon rainforest in the Guyanas, October 2005. Lagrangian modelling of boundary layer (BL) air constrained by measurements is used to derive a horizontal gradient (≈5.6 pmol/mol km −1 ) of CO from the ocean to the rainforest (east to west). This is significantly smaller than that derived from the measurements (16-48 pmol/mol km −1 ), indicating that photochemical production from organic precursors alone cannot explain the observed strong gradient. It appears that HCHO is overestimated by the Lagrangian and chemical box models, which include dry deposition but not exchange with the free troposphere (FT). The relatively short lifetime of HCHO implies substantial BL-FT exchange. The mixing-in of FT air affected by African and South American biomass burning at an estimated rate of 0.12 h −1 increases the CO and decreases the HCHO mixing ratios, improving agreement with measurements. A mean deposition velocity of 1.35 cm/s for H 2 O 2 over the ocean as well as over the rainforest is deduced assuming BL-FT exchange adequate to the results for CO. The measured increase of the organic peroxides from the ocean to the rainforest (≈0.66 nmol/mol d −1 ) is significantly overestimated by the Lagrangian model, even when using high values for the deposition velocity and the entrainment rate. Our results point at either heterogeneous loss of organic peroxides and/or their radical precursors, underestimated photodissociation or missing reaction paths of peroxy radicals not forming peroxides in isoprene chemistry. We calculate a mean integrated daytime net ozone production (NOP) in the Correspondence to: A. Stickler

Atmospheric Chemistry and Physics, 2004

A new method for measuring gas-phase naphthalene in the atmosphere is based on laser-induced fluo... more A new method for measuring gas-phase naphthalene in the atmosphere is based on laser-induced fluorescence at low pressure. The fluorescence spectrum of naphthalene near 308 nm was identified. Naphthalene fluorescence quenching by N 2 , O 2 and H 2 O was investigated in the laboratory. No significant quenching was found 5 for H 2 O with mixing ratio up to 2.5%. The quenching rate of naphthalene fluorescence is (1.98±0.18) ×10 −11 cm 3 molecule −1 s −1 for N 2 , and (2.48±0.08)×10 −10 cm 3 molecule −1 s −1 for O 2 at 297 K. Instrument calibrations were performed with a range of naphthalene mixing ratios between 5 and 80 parts per billion by volume (ppbv, 10 −9 ). In the current instrument configuration, the detection limit is estimated to be about 20 10 parts per trillion by volume (pptv, 10 −12 ) with 2σ confidence and a 1-min integration time. Measurement of atmospheric naphthalene in three cities, Nashville, TN, Houston, TX, and New York City, NY, are presented. Good correlation between naphthalene and major anthropogenic pollutants is found.

J Atmos Chem, 2004

Atmospheric Chemistry and Physics Discussions, 2012

Atmospheric Measurement Techniques Discussions, 2014

Atmospheric Chemistry and Physics, 2013

Science, 2004

Journal of Atmospheric Chemistry, 2000

Atmospheric Environment, 2003

Atmospheric Environment, 2010

Atmospheric Chemistry and Physics, 2011

Atmospheric Chemistry and Physics, 2012

We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemi... more We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO (Diel Oxidant Mechanisms in relation to Nitrogen Oxides) campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O 3 -NO x -VOC-HO x diurnal cycle during conditions characterized by a low NO x regime and small O 3 tendencies (less than 1 ppb per hour). By focusing on the budget equations of chemical species in the mixedlayer model, we show that for species like O 3 , NO and NO 2 , the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the diel cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further deter-mine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

Atmospheric Chemistry and Physics, 2011

Atmospheric Chemistry and Physics, 2007

Atmospheric Chemistry and Physics, 2004