Volatilization Fluxes Research Articles

Volatilização de amônia com aplicação de uréia na superfície do solo, no sistema plantio direto

Com o objetivo de avaliar o efeito dos resíduos culturais de aveia preta (Avena strigosa), dispostos na superfície do solo, nas perdas de N por volatilização de amônia, conduziu-se um experimento a campo, em 2002/03, na UFSM (RS), em um Argissolo Vermelho distrófico arênico. O delineamento experimental foi o inteiramente casualizado, com três repetições. Os tratamentos constituíram da aplicação de uréia no milho, na presença e na ausência de resíduos culturais de aveia, em três épocas (pré-semeadura, semeadura e em cobertura). A uréia foi aplicada a lanço, sem incorporação ao solo, na dose equivalente a 50kg ha-1 de N, em cada época. Os resíduos culturais diminuíram os fluxos de volatilização de amônia quando eles proporcionaram maior umidade do solo no momento da aplicação da uréia, em relação ao solo descoberto. Em condições semelhantes de umidade de solo, entre os tratamentos com e sem resíduos culturais, houve maior volatilização de amônia, quando a uréia foi aplicada sobre os resíduos culturais. Quando ocorreu chuva no dia posterior a aplicação da uréia, não houve efeito dos resíduos culturais na volatilização de amônia. Na soma das três épocas de aplicação de uréia na cultura do milho, a quantidade de amônia volatilizada não diferiu entre os tratamentos com e sem resíduos culturais, com média de 17 % de perda do N-uréia aplicado.

Solar Radiation, Relative Humidity, and Soil Water Effects on Metolachlor Volatilization

Pesticide volatilization is a significant loss pathway that may have unintended consequences in nontarget environments. Field-scale pesticide volatilization involves the interaction of a number of complex variables. There is a need to acquire pesticide volatilization fluxes from a location where several of these variables can be held constant. Accordingly, soil properties, tillage practices, surface residue management, and pesticide formulations were held constant while fundamental information regarding metolachlor volatilization (a pre-emergent pesticide) was monitored over a five-year period as influenced by meteorological variables and soil water content. Metolachlor vapor concentrations were measured continuously for 120 h after each application using polyurethane foam plugs in a logarithmic profile above the soil surface. A flux gradient technique was used to compute volatilization fluxes from metolachlor concentration profiles and turbulent fluxes of heat and water vapor (as determined from eddy covariance measurements). Differences in meteorological conditions and surface soil water contents resulted in variability of the volatilization losses over the years studied. The peak volatilization losses for each year occurred during the first 24 h after application with a maximum flux rate in 2001 (1500 ng m(-2) s(-1)) associated with wet surface soil conditions combined with warm temperatures. The cumulative volatilization losses for the 120-hour period following metolachlor application varied over the years from 5 to 25% of the applied active ingredient, with approximately 87% of the losses occurring during the first 72 h. In all of the years studied, volatilization occurred diurnally and accounted for between 43 and 86% during the day and 14 and 57% during the night of the total measured loss. The results suggest that metolachlor volatilization is influenced by multiple factors involving meteorological, surface soil, and chemical factors.

Prediction of pesticide volatilization with PELMO 3.31

In the current EU risk assessment for pesticide registration, the European Community requires prediction of the concentration of each pesticide in air. A number of mathematical models are used to assess the fate of pesticides in groundwater, surface water and soil. PELMO 3.20 calculates the volatilization fluxes from bare soil and was improved in the new version PELMO 3.31 to include the effect of temperature and sorption in dry soil. The objective of this study was to evaluate the new version of PELMO 3.31 in predicting the pesticide volatilization under field conditions. Procymidone, malathion, and ethoprophos were the test compounds in two different seasons (autumn and winter). Comparing simulation results obtained with PELMO 3.31, after calibration, with the previous version PELMO 3.20 shows that the estimated volatilization results seems improved for malathion, similar or slightly overestimating in the warmer season for ethoprophos, and similar or slightly underestimating in the colder season for procymidone. The new release of PELMO allows a more accurate estimation of pesticides volatilization from soil as function of meteorological factors, especially for medium or low volatility pesticides. Some difficulties remain, such as the determination of the active air layer and the sorption increment with the soil drying.

An improved description of pesticide volatilization: refinement of the pesticide leaching model (PELMO).

The consideration of pesticide volatilization from soil surfaces as an integral component of pesticide fate models is of importance, especially as part of the Predicted Environmental Concentrations (PEC) models used in the registration procedures for pesticides. The Pesticide Leaching Model (PELMO), which is used in the European registration process, was modified to allow for a reliable prediction of volatilization from soil. The previous PELMO version was upgraded by improving the spatiotemporal discretization at the soil surface, improving the empirical description of temperature dependence of Henry's law constants and including increased sorption of pesticides in dry soils. Comparison of predictions with experimental findings revealed the improvements of PELMO to contribute to a more realistic reflection of measurements, particularly at initial stages of the studies. The broad range of literature values of Henry's law constants was shown to have a significant effect on predicted volatilization fluxes. As a main refinement, the tendency of pesticides toward enhanced volatilization under moist conditions was correctly calculated by the improved model. Variations between model predictions and measurements were due to a lack of experimental data on soil sorption under dry conditions and indicated the need for further calibration of the model. The description of water content in the top layer was subject to uncertainty, which was exemplified by an overestimation of soil moisture during the last days of the field study. Thus, future model improvement will be dependent on experimental support to obtain more detailed information on soil-air-water partitioning of pesticides in the top soil layer.

Understanding the tropospheric transport and fate of agricultural pesticides.

Many field monitoring studies have indicated the substantial role of the troposphere as both a sink and transport medium for pesticides. At the same time, this is the least studied and understood environmental compartment in regards to pesticide fate. Although the fundamental principles behind volatilization and tropospheric reactivity are well understood, it is becoming increasingly apparent that the ability to quantitatively measure flux and reaction rates in the air will continue to pose problems for researchers. To date, most deterministic models that try to simulate real world conditions generally fail to provide tropospherically relevant flux and reaction rates because it is virtually impossible to scale down all possible interactions occurring in a near-infinite reservoir. Better field methods for determining flux are emerging and more ambient air monitoring studies are being conducted. This growing database of information, together with an understanding of physicochemical properties and use of expert systems, has increased the predictive capability for estimating volatilization flux of pesticides. Unfortunately, there are very limited environmental data on the tropospheric reaction rates of pesticides, and more experimental studies using semivolatile to low-volatility pesticides or their more volatile homologues are required to validate existing structure-activity relationship (SAR) model predictions. The development of new analytical strategies using elevated temperatures for assessing semivolatile to low-volatility pesticide reaction rates and products may provide an alternative approach to the need for controlled environmental temperature data. Recent international workshops organized by the Health Council of The Netherlands for developing uniform approaches for assessing exposure risks to pesticides in air exemplify efforts to synchronize flux with environmental fate information for determining human health and ecological risks. When more detailed pesticide information is desired, especially in high-use agricultural areas, where exposure to humans and nontarget ecological communities is a major concern, field flux measurements and downwind monitoring, together with experimental fate studies, should be considered. The integration of models, empirical testing, and real world monitoring will provide the ultimate safety net needed for assessing exposure risks to airborne pesticides.

Sea breeze modulated volatilization of polycyclic aromatic hydrocarbons from the Masnou Harbor (NW Mediterranean Sea).

Harbors, marinas, and coastal environments are impacted by important pollutant loadings, particularly of polycyclic aromatic hydrocarbons (PAHs). Air-water exchange is an important process driving the environmental fate of organic pollutants in aquatic environments. However, its relevance as a factor affecting the environmental fate of pollutants from harbor sediments and waters has not been properly assessed, so far, except for few coastal environments. The objective of this study is to quantify the importance of volatilization losses of PAHs from harbor sediments and waters and to study the potential role of sea breeze as a modulator of air-water exchange in coastal environments. The results show that volatilization fluxes from a medium size marina located in the NW Mediterranean sea are relatively high in comparison to those observed in other aquatic systems, particularly for the low molecular weight (MW) compounds. This is consistent with PAHs profiles observed in harbor sediments, which are depleted by the lower MW hydrocarbons. Therefore, volatilization is an important loss of low MW PAHs such as phenanthrene, methyl phenanthrene, dibenzothiophene, etc. Indeed, these PAHs have a residence time of few days in the harbor waters and sediments. Finally, the diurnal trends in volatilization fluxes mimics that of the sea breeze influenced wind speed. These results show the important role that the diurnal sea breeze exerts on the environmental fate of pollutants such as PAHs in coastal environments as a modulator of air-water exchange and as a potential driver of transport of pollutants between adjacent coastal and terrestrial environments.

Reevaluation of air-water exchange fluxes of PCBs in Green Bay and southern Lake Michigan.

Air-water exchange of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) is an import process for the delivery of contaminants to water bodies, as well as for their removal, and is thus a pivotal parameter in the construction of mass balances in aquatic systems. Simultaneous measurements of PCB concentrations in the gas and dissolved phases conducted in Green Bay in 1989 and in southern Lake Michigan in 1994-1995 were used to estimate air-water exchange fluxes. In this work, improved Henry's law constants for PCBs and new mass-transfer rates across the air-water interface were used to update the previous calculations. The new model calculations suggest that the net volatilization flux of PCBs out of Green Bay ranges from +170 to +5300 ng m(-2) day(-1), which is 2-20 times larger than previous estimates. The flux of PCBs in southern Lake Michigan exhibits net volatilization of +0.5 to +230 ng m(-2) day(-1) throughout the study period (May and July 1994, January 1995), whereas previous estimates reported that the net flux was seasonally absorptive. Thus, water-to-air fluxes are more important for the removal of PCBs from both Green Bay and Lake Michigan than previously recognized.

Rate of pesticide volatilization from soil: an experimental approach with a wind tunnel system applied to trifluralin

Pesticide volatilization to the atmosphere may be a major pathway of dissipation closely linked with environmental, physico-chemical and technical factors. Understanding the volatilization process requires systems that make it possible to control some of these factors. Wind tunnels meet to these criteria. The volatilization flux is determined from a mass balance, using the difference in atmospheric pesticide concentration between the entrance and the exit of the tunnel and the airflow rate. An experiment was carried out in June 2000 to study the repeatability of this technique. Volatilization of trifluralin was measured in three wind tunnels for 8 days with a sampling period varying between 3 h and 2 days. Pesticide concentration was determined by trapping by XAD-2 resin in a two-stage cartridge, solvent extraction and analysis by gas chromatography. Cumulated losses through volatilization reached 30% of the measured application dose after 8 days, with a variability of less than 20% between the three tunnels. Approximately 20% remained in the topsoil (0–2 cm), with a variability of 14% between the three tunnels. The decrease in the volatilization flux over time is coherent with the expected theoretical evolution for a volatile pesticide such as trifluralin and with previous experimental works.

Seasonal and annual air-water exchange of polychlorinated biphenyls across Baltimore Harbor and the northern Chesapeake Bay.

As part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS), air-water exchange fluxes of polychlorinated biphenyls (PCBs) were determined along a transect in the Baltimore Harbor from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay to assess the overall contributions of urban source PCBs through air-water exchange and their impacts on coastal waters. Six sites were sampled during three intensive sampling periods in June 1996, February 1997, and July 1997 and at two sites (urban and rural) every ninth day between March 1997 and March 1998 to measure spatial and temporal variability in the PCB air-water exchange fluxes. During the intensive sampling campaigns, net total PCB (t-PCBs) volatilization fluxes ranged between 5 and 2120 ng m(-2) day(-1), varying on both temporal and spatial scales. Volatilization fluxes were highest in February, driven by high winds and elevated dissolved PCB concentrations. Throughout the annual sampling period, t-PCB volatilization fluxes were similar between urban (130 microg m(-2) yr(-1)) and rural (120 microg m(-2) yr(-1)) sites. Approximately 10% of the dissolved t-PCB inventory in the water column in Baltimore Harbor exchanges with the atmosphere each day. From air-water exchange alone, the estimated residence time of dissolved t-PCBs in the harbor is approximately 10 days (estimated hydraulic residence time of water in the harbor is between 7 and 14 days), indicating that air-water exchange is an efficient removal mechanism of t-PCBs from urban coastal waters. Furthermore, the annual flux of t-PCBs volatilizing from Baltimore Harbor is approximately 12% of the gas-phase t-PCB inventory over the water, and at the northern Chesapeake Bay site, the t-PCB flux is approximately 40% of the gas-phase t-PCB inventory. This suggests that air-water exchange of t-PCBs has the potential to be a significant source of PCBs to the rural atmosphere.

A dynamic two-dimensional system for measuring volatile organic compound volatilization and movement in soils.

There is an important need to develop instrumentation that allows better understanding of atmospheric emission of toxic volatile compounds associated with soil management. For this purpose, chemical movement and distribution in the soil profile should be simultaneously monitored with its volatilization. A two-dimensional rectangular soil column was constructed and a dynamic sequential volatilization flux chamber was attached to the top of the column. The flux chamber was connected through a manifold valve to a gas chromatograph (GC) for real-time concentration measurement. Gas distribution in the soil profile was sampled with gas-tight syringes at selected times and analyzed with a GC. A pressure transducer was connected to a scanivalve to automatically measure the pressure distribution in the gas phase of the soil profile. The system application was demonstrated by packing the column with a sandy loam in a symmetrical bed-furrow system. A 5-h furrow irrigation was started 24 h after the injection of a soil fumigant, propargyl bromide (3-bromo-1-propyne; 3BP). The experience showed the importance of measuring lateral volatilization variability, pressure distribution in the gas phase, chemical distribution between the different phases (liquid, gas, and sorbed), and the effect of irrigation on the volatilization. Gas movement, volatilization, water infiltration, and distribution of degradation product (Br-) were symmetric around the bed within 10%. The system saves labor cost and time. This versatile system can be modified and used to compare management practices, estimate concentration-time indexes for pest control, study chemical movement, degradation, and emissions, and test mathematical models.

Microcosm enrichment of 1,3-dichloropropene-degrading soil microbial communities in a compost-amended soil

A microcosm-enrichment approach was used to investigate bacterial populations that may represent 1,3-dichloropropene (1,3-D)-degrading micro-organisms in compost-amended soil. After 8 weeks of incubation, with repeated application of 1,3-D, volatilization fluxes were much lower for compost-amended soil (CM) than with the unamended soils, indicating accelerated degradation due to addition of compost, or development of new microbial populations with enhanced degradation capacity. Denaturing gradient gel electrophoresis (DGGE) profiles of the PCR-amplified region of 16S rDNA genes were used to identify dominant bacterial populations in the fumigant-degrading soil. The DGGE results indicated that specific bacterial types had been enriched, and a more diverse fingerprint was observed in the community derived from the compost-amended soil compared with the unamended soil. Fragments from 16 different DGGE bands were cloned, sequenced and compared with published 16S rDNA sequences. Two clones, designated E1 and E4, were unique to all soils to which compost was added, and corresponded to strains of Pseudomonas and Actinomadura, respectively. The results show that the addition of compost to soil increases specific microbial populations and results in the accelerated degradation of fumigants. Application of compost manure to soil can help degrade soil fumigants at a faster rate.

Dynamic air-water exchange of polychlorinated biphenyls in the New York-New Jersey Harbor Estuary.

Simultaneous measurements of polychlorinated biphenyls (PCBs) in the air and water over Raritan Bay and New York Harbor were taken in July 1998, allowing the first determinations of air-water exchange fluxes for this heavily impacted system. Average gas-phase concentrations of sigmaPCBs were 1.0 ng m(-3) above Raritan Bay and 3.1 ng m(-3) above New York Harbor. A similar gradient was observed for dissolved water concentrations (1.6 and 3.8 ng L(-1), respectively). Shallow slopes of log K(oc) vs log K(ow) plots indicated a colloidal contribution to the dissolved concentrations, and a three-phase partitioning model was therefore applied. PCBs associated with colloids ranged from 6% to 93% for trichloro- to nonachlorobiphenyls, respectively. Air-water gas exchange fluxes of sigmaPCBs exhibited net volatilization for both Raritan Bay at +400 ng m(-2) day(-1) and New York Harbor at +2100 ng m(-2) day(-1). The correction for the colloidal interactions decreased the volatilization flux of sigmaPCBs by about 15%. Net air-water exchange fluxes of PCBs are expected to remain positive throughout the year due to the large water-air fugacity gradient and relatively constant seasonal water concentrations. The volatilization fluxes are approximately 40 times greater than atmospheric deposition of PCBs via both wet and dry particle deposition, suggesting that the estuary acts as a net source of PCBs to the atmosphere year-round.

COUPLING DIAZINON VOLATILIZATION AND WATER EVAPORATION IN UNSATURATED SOILS: I. WATER TRANSPORT

Volatilization of pesticides from soil is one of the key processes causing transport of chemicals to non-target areas. This study focuses on how water transport in the surface soil affects volatilization of pesticides. Volatilization of soil-incorporated diazinon [O, O diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate] was measured under different initial soil-water contents and soil-water evaporation conditions. These conditions were varied by passing wet air and dry N2 alternately across the soil surface. When dry sweep gas (N2) was used in high initial water content columns, diazinon volatilization was accelerated as a result of appreciable upward water flow. When upward water flow was insufficient to meet evaporative demand, soil-water content at the soil surface was quickly reduced below a threshold, and diazinon volatilization started to decrease exponentially because of diazinon adsorption on the dry soil surfaces. When the sweep gas was switched to humidified air, the soil surface adsorbed water and diazinon volatilization increased dramatically. A numerical model was developed to simulate pesticide transport in soil for isothermal conditions. The calculated and measured diazinon volatilization fluxes agreed well, but the model overestimated diazinon concentrations in the deeper depths of the soil significantly.

Evidence for Dynamic Air−Water Exchange of PCDD/Fs: A Study in the Raritan Bay/Hudson River Estuary

The first detailed evidence for dynamic air−water exchange of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) is presented. Samples of air (340−380 m3) and water (33−60 L) were taken simultaneously during July 1998 at two sites in the lower Hudson River Estuary, NY. The atmospheric gas and particulate phases and the aqueous dissolved and particulate phases were analyzed for di- to octa-CDD/Fs. All the homologue groups were routinely detected by HRGC-HRMS, with detection limits for the homologue groups 1 pg/sample. Cl2DDs, OCDD, and Cl2DFs were the most abundant homologues in the water, and the Cl2DDs were the most abundant in the air (4.3−7.6 pg/m3). The Cl2DD/Fs and Cl7/8DD/Fs were 25−53% and 78−99% associated with the water particulate phase, respectively. The likelihood of sampling artifacts influencing the apparent dissolved/particulate partitioning of the higher chlorinated congeners is discussed. Water concentrations were constant over the sampling period, while atmospheric concentrations varied with air mass origin. The fugacity ratios between the dissolved phase in water and the gas phase in air were usually >1, implying a net volatilization flux. Evidence for outgassing of the lower chlorinated homologues, obtained by the simultaneous measurement of air over adjacent land and water, provided further support for the outgassing of the lower chlorinated homologues from the water body.

Cumulative losses of buried volatile organic chemicals

New analytical expressions are presented for cumulative losses of the Jury et al. [1983] behavior assessment type of model for volatile organic chemicals buried in soil vadose zones. These expressions are for the soil‐surface cumulative volatilization flux and subsurface cumulative degradation and mass loss. At the soil surface a flux boundary condition is used which includes a nonzero, atmospheric volatile concentration. Numerical results for time‐dependent surface flux and cumulative quantities are presented for this boundary condition.

Sources of Chlorpyrifos and Dacthal to a Small Canadian Prairie Watershed

Atmospheric deposition and air−water exchange of two semivolatile pesticides, Dacthal and chlorpyrifos, were compared in a small agricultural watershed in southern Manitoba, Canada, between 1994 and 1996. Dacthal was not used in the watershed nor in the surrounding region. Dacthal concentrations were derived from long-range transport and deposition processes and were lower than those of chlorpyrifos, which was applied locally each year of the study. Maximum concentrations of chlorpyrifos in air (103 ng/m3), precipitation (38 ng/L), and creek water (105 ng/L) were observed during local application periods. The highest Dacthal concentrations (4 ng/L) observed in precipitation occurred during intervals when its use in the U.S. was expected, although a seasonal relationship was not established. Precipitation and gas exchange across the air−water boundary were important pathways of movement for both chlorpyrifos and Dacthal. A net volatilization flux from the entire creek surface was observed for chlorpyrifos ...

Diffusive Exchange of Polycyclic Aromatic Hydrocarbons across the Air−Water Interface of the Patapsco River, an Urbanized Subestuary of the Chesapeake Bay

Air−water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997 and March 1998 to measure spatial, daily, and annual variability in the fluxes. The direction and magnitude of the daily fluxes of individual PAHs were strongly influenced by the wind speed and direction, by the air temperature, and by the highly variable PAH concentrations in the gas and dissolved phases. Individual fluxes ranged from 14 200 ng m-2 day-1 net volatilization of fluorene during high winds to 11 400 ng m-2 day-1 net absorption of phenanthrene when prevailing winds blowing from the northwest across the city of Baltimore elevated gaseous PAH concentrations over the water. The largest PAH volatilization fluxes occurred adjacent...

Atmospheric volatilization of methyl bromide, 1,3-dichloropropene, and propargyl bromide through two plastic films: transfer coefficient and temperature effect

Atmospheric emission of methyl bromide (MeBr) and its potential alternative chemicals such as 1,3-dichloropropene (1,3-D) and propargyl bromide (PrBr) can contribute to air pollution and ozone depletion (for MeBr). One of the main sources of these chemicals is from agricultural soil fumigation. To understand the volatilization dynamics, emission of MeBr, 1,3-D, and PrBr through a polyethylene-based high-barrier film (HBF) and a virtually impermeable film (VIF) was measured using an air flow and sampling system that produced >90% mass balance. The experiment was conducted outdoors and was subjected to ambient daily temperature variations. The HBF film was found to be very permeable to 1,3-D and PrBr, but somewhat less permeable to MeBr. The VIF film was very impermeable to 1,3-D, PrBr, or MeBr. Measured volatilization flux, in general, exhibited strong diurnal variations which were controlled by film temperature. Unlike the HBF film, a time lag (∼12 h) was observed between high-temperatures and high-emission flux values for the VIF film. An impermeable film may be used as an effective means of controlling the atmospheric emission of MeBr and its alternative chemicals.

Automated Sequential Sampler for Collection of Highly Volatile Atmospheric Contaminants

AbstractRapid and accurate measurement of atmospheric concentrations of highly volatile organic compounds is important in obtaining reliable information for the assessment of environmental pollution or the volatilization mechanisms of the chemicals. Nonmechanized sample collection requires intensive labor and effort, and may cause large random or systematic errors. An automated solenoid switching system was developed to assist in obtaining precise environmental concentrations of highly volatile organic compounds. The design, construction, and operation are described in the paper for potential application in similar studies. Using this sampling system, two experiments were conducted to determine atmospheric volatilization flux density of three highly volatile and reactive organic compounds (methyl bromide, 1,3‐dichloropropene, and propargyl bromide). The automated solenoid switching system significantly reduced the requirements for labor and time. Results from the two experiments indicate that reliable sample collection was achieved. The automated sampling system was also relatively inexpensive and can be easily modified to accommodate a variety of sources, sampling intervals, and multiple number of solenoid valves.

Field‐Scale Metolachlor Volatilization Flux Estimates from Broadcast and Banded Application Methods in Central Iowa

AbstractVolatilization of pesticides has been considered to be a large part of the loss from fields after application; however, there have been relatively few studies conducted to quantify the amount lost to the atmosphere. This study was designed to evaluate volatilization rates of a preemergent herbicide Dual [a.i. metolachlor 2.24 kg ha−1 (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)‐acetamide)] from two fields (175 and 45 ha) in central Iowa under contrasting tillage operations and pesticide application scenarios. Metolachlor vapor was trapped using polyurethane foam plugs at six heights on a profile mast. Average concentrations were measured at each height every 2 h for the first 4 d after application, then every 4 h thereafter. Volatilization rates were calculated with a flux‐gradient technique using data from Bowen ratio and eddy correlation measurements. Flux profile concentrations of metolachlor were large during the first 24 h and quickly declined for the duration of the study. There was approximately a threefold greater cumulative volatilization loss of applied metolachlor from the broadcast (22%) treatment than from the banded treatment (6%) for the 10‐d study period. Metolachlor volatilization was affected by residue cover, spatial concentration on the surface, and timing of precipitation.