Joan Willey - Academia.edu (original) (raw)
Papers by Joan Willey
Journal of Chemical Education, 2004
Analysis of weather patterns on a synoptic or regional scale is the common direction of study in ... more Analysis of weather patterns on a synoptic or regional scale is the common direction of study in air pollution meteorology with few studies analyzing weather conditions proximal to collection sites. A study that focuses on local weather conditions may lead to better understanding and more accurate forecasting of rain water chemistry than synoptic or regional scale studies. The objective of this project is to determine the relationship between local weather patterns and rain water chemistry in Wilmington, NC. Daily and hourly meteorological data (average temperature, relative humidity, wind speed and direction, and maximum and minimum temperatures) were collected for the 48 hour period prior to each rain event. In addition, the nitrate and sulfate concentrations were obtained from the Marine and Atmospheric Chemistry Research Laboratory (MACRL) at UNCW. Data analysis of local weather conditions 48 hours prior to 24 storm events, including review of descriptive statistics, graphical a...
Chemosphere, 2016
h i g h l i g h t s Fresh surface waters and estuarine waters are generally a net sink for atmosp... more h i g h l i g h t s Fresh surface waters and estuarine waters are generally a net sink for atmospheric ethanol. Coastal waters can be either a sink or source of atmospheric ethanol. Ethanol (up to 598 nM) was found in each freshwater, estuarine and coastal sample collected.
Chemosphere, 2015
h i g h l i g h t s A HS-SPME method optimized for the detection of VOCs in rainwater. Rainwater ... more h i g h l i g h t s A HS-SPME method optimized for the detection of VOCs in rainwater. Rainwater was collected and analyzed for VOCs over a one-year period (111 samples). Methylfuran occurred most frequently (detected in 86% of samples). Rainwater is not an effective removal mechanism of BTEX at this location (<0.1%).
Atmospheric Chemistry and Physics Discussions, 2014
This work reports the first detailed analysis of methanol concentrations in rainwater. Methanol c... more This work reports the first detailed analysis of methanol concentrations in rainwater. Methanol concentrations measured in 49 rain events collected between 28 August 2007 to 10 July 2008 in Wilmington, NC, USA, ranged from below the detection limit of 6 nM to 9.3 µM with a volume weighted average concentration of 1.2 ± 0.2 µM. Methanol concentrations in rainwater were up to ∼ 200× greater than concentrations observed in marine waters indicating wet deposition as a potential significant source to marine waters. Assuming these methanol concentrations are an appropriate proxy for global methanol rainwater concentrations the global methanol wet deposition sink is estimated as 20 Tg yr −1 which implies previous methanol budgets underestimate removal by precipitation. Methanol concentrations did not correlate with H + , NO − 3 , and NSS, which suggest that the dominant source of the alcohol to rainwater is not anthropogenic. However, methanol concentrations were strongly correlated with acetaldehyde which has a primarily biogenic input. Methanol volume weighted concentration during the growing season (1.5 + 0.3 µM) was more than double that of the non-growing season (0.7 + 0.1 µM), further promoting biogenic emissions as the primary cause of fluctuating methanol concentrations. Methanol concentrations peaked in rainwater collected between the time period 12:00-06:00 p.m. Peaking during this period of optimal sunlight implies a direct relationship to photochemical methanol production but there are also increases in biogenic activity during this time period. Rain events with terrestrial origins had higher concentrations than those of marine origin demonstrating the significance of the continental source of methanol in rainwater.
Atmospheric Environment, 2015
Limnol. Oceanogr, 2008
Rainwater hydrophobic extractable dissolved organic matter (EDOM) contains ligand (s) that comple... more Rainwater hydrophobic extractable dissolved organic matter (EDOM) contains ligand (s) that completely prevent Fe (II) oxidation for at least 4 h after rain is mixed with seawater. The EDOM Fe (II) complex is at least of comparable strength to the ferrozine ...
Atmospheric Environment, 2001
Concentrations of formic and acetic acids in Wilmington, North Carolina, USA, rainwater collected... more Concentrations of formic and acetic acids in Wilmington, North Carolina, USA, rainwater collected between 1996 and 1998 have increased dramatically since an earlier study conducted at the same site between 1987 and 1989. The current volume-weighted concentrations of acetic acid are within the range of values reported for urban locations whereas values from the earlier study at this site were similar to those obtained for rural locations. The ratios of formic to acetic acids (F : A) in the current study (approximately 1 : 1) are considerably lower than those previously reported (approximately 2.7 : 1). Current F : A's are similar to F : A's from direct automobile emissions. Increases in formic and acetic acid concentrations and the shift in formic to acetic acid ratios likely re#ect the impact of extensive population growth in the surrounding region. Assuming increases in formic and acetic acid concentrations result from increased anthropogenic sources, we estimate at least 1/2 of the formic and at least 2/3 of the acetic acid in Wilmington, NC growing season rainwater results from anthropogenic sources.
Atmospheric Environment, 2013
h i g h l i g h t s < NMR spectra and integrations show great variability between rain events. < ... more h i g h l i g h t s < NMR spectra and integrations show great variability between rain events. < Season and storm origin influence rainwater NMR spectral pattern and intensity. < Spring rains contained a high percentage of carbohydrate like components. < Marine winter rains had a high alkyl signal. < Anthropogenic (phthallic and terephthallic acids) and biogenic signals were observed.
Atmospheric Chemistry and Physics, 2013
Atmospheric …, 2010
Concentrations of formic and acetic acid from January 2008 through March 2009 were compared to tw... more Concentrations of formic and acetic acid from January 2008 through March 2009 were compared to two previous studies at this location (conducted in 1987e1990 and 1996e1998) in order to quantify the extent to which temporal changes in DOC and pH can be explained by changes in these organic acids. The volume weighted 2008 formic and acetic acid concentrations (5.6 and 2.6 mM respectively) have decreased dramatically compared with those observed during the 1996e1998 study (9.9 and 7.3 mM) and are also lower than concentrations observed in the 1987e1990 study (7.4 and 3.6 mM). Changes in formic and acetic acids between 1996e97 and 2008 can account for approximately 50% of the DOC change and 40% of the H þ change in rainwater over this same time period. These changes are most pronounced during the growing season, which is also the tourist and high traffic season at this location. Determining causation of these changes is difficult due to multiple biogenic and anthropogenic sources. However, the ratio of formic to acetic acid has also reverted back to a value consistent with reduced vehicular emissions, possibly related to the introduction of improved emission control technology including the use of reformulated gasoline in the late 1990's. Long term monitoring of seasonal, annual, and decadal trends will be of critical importance for evaluating the effects of future changes to atmospheric inputs such as the increased use of ethanol and other alternative fuels.
Aquatic Sciences, 2009
. The concentration of Fe(II) has decreased more than 50% since 2001 in both winter and summer r... more . The concentration of Fe(II) has decreased more than 50% since 2001 in both winter and summer rain collected in Wilmington, North Carolina, USA. Storage experiments performed on rain collected during the summer of 2008 revealed rapid oxidation of Fe(II) by hydrogen peroxide with second order rate constants between 2 and 48 M−1 s−1. The rapid oxidation of Fe(II) in these
Atmospheric Environment, 2008
... The Hg 0 is thermally desorbed from the gold columns and detected via cold vapor atomic fluor... more ... The Hg 0 is thermally desorbed from the gold columns and detected via cold vapor atomic fluorescence (Gill and Fitzgerald, 1987). ... Tropical storm Ernesto formed as a tropical depression just north of Venezuela (12.9°N, 62.4°W) on 24 August 2006 and gained strength as in ...
Marine Ecology-progress Series, 1999
Bioassays indicate addition of hydrogen peroxide in concentrations similar to rain sometimes decr... more Bioassays indicate addition of hydrogen peroxide in concentrations similar to rain sometimes decreases chlorophyll a (chl a) production in surface Gulf Stream seawater. Bioassays were conducted on shipboard in the spring and autumn of 1993, 1994, and 1995. using surface Gulf Stream seawater collected off the coast of North Carolina. Chl a increases were observed after addition of FeC13 (in 1 of 5 bioassays), iron (111) EDTA (6 of 6 bioassays), or EDTA alone (4 of 4 bioassays). The chl a increases were suppressed significantly in 7 of 11 of these bioassays when the bioassay seawater was initially diluted by 1 % with a 30 or 40 p M solution of hydrogen peroxide (a concentration similar to rainwater). Hydrogen peroxide induced inhibition of chl a production was not observed in bioassays in w h~c h chl a increased in response to addltion of nitrate or ammonium, hence the growth inhibition was associated with added metal or complexing agent. Rainwater therefore plays a complex role in primary productivity in surface seawater, with the specific effect dependent upon rainwater concentrations of nitrate, ammonium, trace metals and hydrogen peroxide, as well as on the extent of nitrogen limitation and the oxidant concentration in the surface seawater. KEY WORDS: Hydrogen peroxide. Rainwater. Chlorophyll a. Bioassays. Gulf Stream. Seawater O Inter-Research 1999 Resale o f full article not permitted
Environmental science & …, 2006
The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% duri... more The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+(aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+(aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+(aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean.
… science & technology, 2003
Significant concentrations of Fe(II) were produced upon irradiation of authentic rainwater with s... more Significant concentrations of Fe(II) were produced upon irradiation of authentic rainwater with simulated sunlight. The magnitude of photoproduction was dependent on initial Fe(II), Fe(III), and hydrogen ion concentrations, with more Fe(II) photoproduction when initial Fe(III) and H+ concentrations were high and initial Fe(II) concentrations were low. An equation was developed that accurately predicts photoproduction of Fe(II) in rainwater based on initial Fe speciation values and pH. The quantum yield of Fe(II) photochemical production in rain decreased dramatically with increasing wavelength and decreasing energy of incoming radiation with the average quantum yield at 265 nm approximately an order of magnitude greater than at 546 nm. Probable photochemical precursors of Fe(II) in authentic rain include iron(III) oxalate, iron(III) hydroxide, and an undefined Fe(III) complex. The wavelength-dependent Fe(II) production was modeled using the average Fe(II) efficiency spectrum, an average rainwater absorption spectrum, and the modeled actinic flux for temperate latitudes in both summer and winter. The response spectrum has the highest photoproduction of Fe(II) in summer and winter at 325 and 330 nm, respectively, with greater production in summer rain due to increased actinic flux and longer hours of irradiation.
AGU Spring …, 2007
The abundance and spectral characteristics of chromophoric dissolved organic matter (CDOM) was de... more The abundance and spectral characteristics of chromophoric dissolved organic matter (CDOM) was determined in atmospheric waters in Wilmington, North Carolina USA over an 18 month sampling period. Fluorescence excitation - emission spectra (EEMs) of condensed ...
Atmospheric …, 2010
Photochemical production of formaldehyde (HCHO) was measured in rainwater from 13 precipitation e... more Photochemical production of formaldehyde (HCHO) was measured in rainwater from 13 precipitation events in Wilmington, North Carolina, USA under conditions of simulated sunlight. HCHO concentrations increased in all samples irradiated with no changes observed in dark controls. HCHO photoproduction rates were strongly correlated with dissolved organic carbon (DOC) suggesting HCHO was derived from direct or indirect photolysis of rainwater DOC. The higher photoproduction rates (0.03e2.9 mM h À1) relative to those reported for surface waters suggests that rainwater DOC is more photolabile in terms of HCHO production than surface waters. HCHO photoproduction rates were higher in growing season (1.0 AE 1.0 mM h À1) compared to non-growing season (0.08 AE 0.05 mM h À1) even when rates were normalized for DOC (6.8 AE 3.6 mM h À1 mM C À1 versus 1.8 AE 1.0 mM h À1 mM C À1). The higher growing season rate may be related to seasonal differences in the composition of DOC as evidenced by differences in fluorescence per unit carbon of rainwater samples. Irradiation of C18 extracts of rainwater also produced HCHO, but at lower rates compared to corresponding whole rain samples, suggesting that hydrophyllic components of rainwater play a role in HCHO photoproduction. Our results indicate that photolysis of rainwater DOC produces significant amounts of HCHO, and possibly other low molecular weight organic compounds, likely increasing its reactivity and bioavailability.
Journal of Chemical Education, 2004
Analysis of weather patterns on a synoptic or regional scale is the common direction of study in ... more Analysis of weather patterns on a synoptic or regional scale is the common direction of study in air pollution meteorology with few studies analyzing weather conditions proximal to collection sites. A study that focuses on local weather conditions may lead to better understanding and more accurate forecasting of rain water chemistry than synoptic or regional scale studies. The objective of this project is to determine the relationship between local weather patterns and rain water chemistry in Wilmington, NC. Daily and hourly meteorological data (average temperature, relative humidity, wind speed and direction, and maximum and minimum temperatures) were collected for the 48 hour period prior to each rain event. In addition, the nitrate and sulfate concentrations were obtained from the Marine and Atmospheric Chemistry Research Laboratory (MACRL) at UNCW. Data analysis of local weather conditions 48 hours prior to 24 storm events, including review of descriptive statistics, graphical a...
Chemosphere, 2016
h i g h l i g h t s Fresh surface waters and estuarine waters are generally a net sink for atmosp... more h i g h l i g h t s Fresh surface waters and estuarine waters are generally a net sink for atmospheric ethanol. Coastal waters can be either a sink or source of atmospheric ethanol. Ethanol (up to 598 nM) was found in each freshwater, estuarine and coastal sample collected.
Chemosphere, 2015
h i g h l i g h t s A HS-SPME method optimized for the detection of VOCs in rainwater. Rainwater ... more h i g h l i g h t s A HS-SPME method optimized for the detection of VOCs in rainwater. Rainwater was collected and analyzed for VOCs over a one-year period (111 samples). Methylfuran occurred most frequently (detected in 86% of samples). Rainwater is not an effective removal mechanism of BTEX at this location (<0.1%).
Atmospheric Chemistry and Physics Discussions, 2014
This work reports the first detailed analysis of methanol concentrations in rainwater. Methanol c... more This work reports the first detailed analysis of methanol concentrations in rainwater. Methanol concentrations measured in 49 rain events collected between 28 August 2007 to 10 July 2008 in Wilmington, NC, USA, ranged from below the detection limit of 6 nM to 9.3 µM with a volume weighted average concentration of 1.2 ± 0.2 µM. Methanol concentrations in rainwater were up to ∼ 200× greater than concentrations observed in marine waters indicating wet deposition as a potential significant source to marine waters. Assuming these methanol concentrations are an appropriate proxy for global methanol rainwater concentrations the global methanol wet deposition sink is estimated as 20 Tg yr −1 which implies previous methanol budgets underestimate removal by precipitation. Methanol concentrations did not correlate with H + , NO − 3 , and NSS, which suggest that the dominant source of the alcohol to rainwater is not anthropogenic. However, methanol concentrations were strongly correlated with acetaldehyde which has a primarily biogenic input. Methanol volume weighted concentration during the growing season (1.5 + 0.3 µM) was more than double that of the non-growing season (0.7 + 0.1 µM), further promoting biogenic emissions as the primary cause of fluctuating methanol concentrations. Methanol concentrations peaked in rainwater collected between the time period 12:00-06:00 p.m. Peaking during this period of optimal sunlight implies a direct relationship to photochemical methanol production but there are also increases in biogenic activity during this time period. Rain events with terrestrial origins had higher concentrations than those of marine origin demonstrating the significance of the continental source of methanol in rainwater.
Atmospheric Environment, 2015
Limnol. Oceanogr, 2008
Rainwater hydrophobic extractable dissolved organic matter (EDOM) contains ligand (s) that comple... more Rainwater hydrophobic extractable dissolved organic matter (EDOM) contains ligand (s) that completely prevent Fe (II) oxidation for at least 4 h after rain is mixed with seawater. The EDOM Fe (II) complex is at least of comparable strength to the ferrozine ...
Atmospheric Environment, 2001
Concentrations of formic and acetic acids in Wilmington, North Carolina, USA, rainwater collected... more Concentrations of formic and acetic acids in Wilmington, North Carolina, USA, rainwater collected between 1996 and 1998 have increased dramatically since an earlier study conducted at the same site between 1987 and 1989. The current volume-weighted concentrations of acetic acid are within the range of values reported for urban locations whereas values from the earlier study at this site were similar to those obtained for rural locations. The ratios of formic to acetic acids (F : A) in the current study (approximately 1 : 1) are considerably lower than those previously reported (approximately 2.7 : 1). Current F : A's are similar to F : A's from direct automobile emissions. Increases in formic and acetic acid concentrations and the shift in formic to acetic acid ratios likely re#ect the impact of extensive population growth in the surrounding region. Assuming increases in formic and acetic acid concentrations result from increased anthropogenic sources, we estimate at least 1/2 of the formic and at least 2/3 of the acetic acid in Wilmington, NC growing season rainwater results from anthropogenic sources.
Atmospheric Environment, 2013
h i g h l i g h t s < NMR spectra and integrations show great variability between rain events. < ... more h i g h l i g h t s < NMR spectra and integrations show great variability between rain events. < Season and storm origin influence rainwater NMR spectral pattern and intensity. < Spring rains contained a high percentage of carbohydrate like components. < Marine winter rains had a high alkyl signal. < Anthropogenic (phthallic and terephthallic acids) and biogenic signals were observed.
Atmospheric Chemistry and Physics, 2013
Atmospheric …, 2010
Concentrations of formic and acetic acid from January 2008 through March 2009 were compared to tw... more Concentrations of formic and acetic acid from January 2008 through March 2009 were compared to two previous studies at this location (conducted in 1987e1990 and 1996e1998) in order to quantify the extent to which temporal changes in DOC and pH can be explained by changes in these organic acids. The volume weighted 2008 formic and acetic acid concentrations (5.6 and 2.6 mM respectively) have decreased dramatically compared with those observed during the 1996e1998 study (9.9 and 7.3 mM) and are also lower than concentrations observed in the 1987e1990 study (7.4 and 3.6 mM). Changes in formic and acetic acids between 1996e97 and 2008 can account for approximately 50% of the DOC change and 40% of the H þ change in rainwater over this same time period. These changes are most pronounced during the growing season, which is also the tourist and high traffic season at this location. Determining causation of these changes is difficult due to multiple biogenic and anthropogenic sources. However, the ratio of formic to acetic acid has also reverted back to a value consistent with reduced vehicular emissions, possibly related to the introduction of improved emission control technology including the use of reformulated gasoline in the late 1990's. Long term monitoring of seasonal, annual, and decadal trends will be of critical importance for evaluating the effects of future changes to atmospheric inputs such as the increased use of ethanol and other alternative fuels.
Aquatic Sciences, 2009
. The concentration of Fe(II) has decreased more than 50% since 2001 in both winter and summer r... more . The concentration of Fe(II) has decreased more than 50% since 2001 in both winter and summer rain collected in Wilmington, North Carolina, USA. Storage experiments performed on rain collected during the summer of 2008 revealed rapid oxidation of Fe(II) by hydrogen peroxide with second order rate constants between 2 and 48 M−1 s−1. The rapid oxidation of Fe(II) in these
Atmospheric Environment, 2008
... The Hg 0 is thermally desorbed from the gold columns and detected via cold vapor atomic fluor... more ... The Hg 0 is thermally desorbed from the gold columns and detected via cold vapor atomic fluorescence (Gill and Fitzgerald, 1987). ... Tropical storm Ernesto formed as a tropical depression just north of Venezuela (12.9°N, 62.4°W) on 24 August 2006 and gained strength as in ...
Marine Ecology-progress Series, 1999
Bioassays indicate addition of hydrogen peroxide in concentrations similar to rain sometimes decr... more Bioassays indicate addition of hydrogen peroxide in concentrations similar to rain sometimes decreases chlorophyll a (chl a) production in surface Gulf Stream seawater. Bioassays were conducted on shipboard in the spring and autumn of 1993, 1994, and 1995. using surface Gulf Stream seawater collected off the coast of North Carolina. Chl a increases were observed after addition of FeC13 (in 1 of 5 bioassays), iron (111) EDTA (6 of 6 bioassays), or EDTA alone (4 of 4 bioassays). The chl a increases were suppressed significantly in 7 of 11 of these bioassays when the bioassay seawater was initially diluted by 1 % with a 30 or 40 p M solution of hydrogen peroxide (a concentration similar to rainwater). Hydrogen peroxide induced inhibition of chl a production was not observed in bioassays in w h~c h chl a increased in response to addltion of nitrate or ammonium, hence the growth inhibition was associated with added metal or complexing agent. Rainwater therefore plays a complex role in primary productivity in surface seawater, with the specific effect dependent upon rainwater concentrations of nitrate, ammonium, trace metals and hydrogen peroxide, as well as on the extent of nitrogen limitation and the oxidant concentration in the surface seawater. KEY WORDS: Hydrogen peroxide. Rainwater. Chlorophyll a. Bioassays. Gulf Stream. Seawater O Inter-Research 1999 Resale o f full article not permitted
Environmental science & …, 2006
The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% duri... more The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+(aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+(aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+(aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean.
… science & technology, 2003
Significant concentrations of Fe(II) were produced upon irradiation of authentic rainwater with s... more Significant concentrations of Fe(II) were produced upon irradiation of authentic rainwater with simulated sunlight. The magnitude of photoproduction was dependent on initial Fe(II), Fe(III), and hydrogen ion concentrations, with more Fe(II) photoproduction when initial Fe(III) and H+ concentrations were high and initial Fe(II) concentrations were low. An equation was developed that accurately predicts photoproduction of Fe(II) in rainwater based on initial Fe speciation values and pH. The quantum yield of Fe(II) photochemical production in rain decreased dramatically with increasing wavelength and decreasing energy of incoming radiation with the average quantum yield at 265 nm approximately an order of magnitude greater than at 546 nm. Probable photochemical precursors of Fe(II) in authentic rain include iron(III) oxalate, iron(III) hydroxide, and an undefined Fe(III) complex. The wavelength-dependent Fe(II) production was modeled using the average Fe(II) efficiency spectrum, an average rainwater absorption spectrum, and the modeled actinic flux for temperate latitudes in both summer and winter. The response spectrum has the highest photoproduction of Fe(II) in summer and winter at 325 and 330 nm, respectively, with greater production in summer rain due to increased actinic flux and longer hours of irradiation.
AGU Spring …, 2007
The abundance and spectral characteristics of chromophoric dissolved organic matter (CDOM) was de... more The abundance and spectral characteristics of chromophoric dissolved organic matter (CDOM) was determined in atmospheric waters in Wilmington, North Carolina USA over an 18 month sampling period. Fluorescence excitation - emission spectra (EEMs) of condensed ...
Atmospheric …, 2010
Photochemical production of formaldehyde (HCHO) was measured in rainwater from 13 precipitation e... more Photochemical production of formaldehyde (HCHO) was measured in rainwater from 13 precipitation events in Wilmington, North Carolina, USA under conditions of simulated sunlight. HCHO concentrations increased in all samples irradiated with no changes observed in dark controls. HCHO photoproduction rates were strongly correlated with dissolved organic carbon (DOC) suggesting HCHO was derived from direct or indirect photolysis of rainwater DOC. The higher photoproduction rates (0.03e2.9 mM h À1) relative to those reported for surface waters suggests that rainwater DOC is more photolabile in terms of HCHO production than surface waters. HCHO photoproduction rates were higher in growing season (1.0 AE 1.0 mM h À1) compared to non-growing season (0.08 AE 0.05 mM h À1) even when rates were normalized for DOC (6.8 AE 3.6 mM h À1 mM C À1 versus 1.8 AE 1.0 mM h À1 mM C À1). The higher growing season rate may be related to seasonal differences in the composition of DOC as evidenced by differences in fluorescence per unit carbon of rainwater samples. Irradiation of C18 extracts of rainwater also produced HCHO, but at lower rates compared to corresponding whole rain samples, suggesting that hydrophyllic components of rainwater play a role in HCHO photoproduction. Our results indicate that photolysis of rainwater DOC produces significant amounts of HCHO, and possibly other low molecular weight organic compounds, likely increasing its reactivity and bioavailability.