Night-time Levels Research Articles

Surface ozone scenario and air quality in the north-central part of India

Tropospheric pollutants including surface ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO) and meteorological parameters were measured at a traffic junction (78°2′ E and 27°11′ N) in Agra, India from January 2012 to December 2012. Temporal analysis of pollutants suggests that annual average mixing ratios of tropospheric pollutants were: O3 — 22.97±23.36ppbV, NO2 — 19.84±16.71ppbV and CO — 0.91±0.86ppmV, with seasonal variations of O3 having maximum mixing ratio during summer season (32.41±19.31ppbV), whereas lowest was found in post-monsoon season (8.74±3.8ppbV). O3 precursors: NO2 and CO, showed inverse relationship with O3. Seasonal variation and high O3 episodes during summer are associated with meteorological parameters such as high solar radiation, atmospheric temperature and transboundary transport. The interdependence of these variables showed a link between the daytime mixing ratios of O3 with the nighttime level of NO2. The mixing ratios of CO and NO2 showed tight correlations, which confirms the influence of vehicular emissions combined with other anthropogenic activities due to office/working hours, shallowing, and widening of boundary layer. FLEXTRA backward trajectories for the O3 episode days clearly indicate the transport from the NW and W to S/SE and SW direction at Agra in different seasons.

Low levels of serum total antioxidant capacity and presence at admission and absence at discharge of a day/night change as a marker of acute paranoid schizophrenia relapse

BackgroundAn oxidant-antioxidant system dysregulation has been described as a schizophrenia pathophysiological base. The total antioxidant capacity (TAC) is one measure of the antioxidant capacity of a system. Day/night concentration changes is a biological characteristic of hormones such as melatonin or cortisol. There is no information about TAC day/night changes in schizophrenia. AimsStudying the existence of a day/night TAC change in schizophrenia. MethodForty-three DSM-IV paranoid schizophrenia inpatients participated in the study. Thirty healthy subjects matched by age and gender acted as control group. Blood was sampled at 12:00 and 00:00h the day after admission and the day before discharge. Serum TAC was measured by the ABTS radical cation technique and expressed in Trolox mmol/L. ResultsPatients had significantly lower TAC levels at admission and discharge (12:00 and 00:00) than controls. At admission patients had a TAC day/night change, with higher day-time than night-time levels (0.66±0.14 vs 0.60±0.15) as well as healthy subjects (0.83±0.07 vs 0.77±0.11). At discharge patients had a similar TAC level at 12:00 and 00:00 (0.64±0.15 vs 0.63±0.14). ConclusionSchizophrenic patients present a deficit of the antioxidant system. The initial presence and the later absence of a day/night change deserves future studies.

O impacto da queima doméstica de biomassa lenhosa nos níveis de PM2,5 na cidade de Bragança, Portugal

We evaluated the influence of residential firewood combustion in the PM2,5 fraction of the atmospheric particulate matter in the city of Bragança, Portugal. Day and night time measurements were carried out between December 2013 and May 2014 in 35 urban sampling points. We also collected data on potential influencing factors of air particle concentration which we related statistically with PM2,5 observation data. Temporal variation and spatial patterning of atmospheric PM2,5 concentrations highlighted the contribution of PM2,5 emissions from domestic firewood use. Night time levels of PM2,5 were in general higher in areas of lower altitude, higher population density and higher firewood combustion intensity. Our results also indicated that during the study period, mean daily PM2,5concentrations were higher than the World Health Organization reference level in more than half of the city area. This study strengthened the importance of monitoring and controlling this source of atmospheric pollution in cities of high use of firewood for energy.

Melatonin Release and Polysomnographic Architecture in Patients with Mild to Moderate Depression

Objectives: The association of serum melatonin levels with polysomnographic sleep parameters were investigated in mild to moderate depressed patients. Methods: Seventy patients with mild to moderate depression (mean age 49.43 ± 6.70) were selected in the study. All patients underwent two successive overnight polysomnography recordings. Venous blood samples were obtained from the patients of two groups at 21:00 h and 6:00 h before and after performing polysomnography. Serum was separated and kept at -80°C. The serum melatonin levels were analysed using microplate reader. Results: Early morning release of melatonin was significantly correlated with sleep latency (P=0.0026, r=0.4630), [CI=0.3249 to 1.426], sleep efficiency (P=0.049, r=0.3123), [CI=0.01253 to 0.3180] and total sleep time (P=0.006, r=0.516), [CI=0.04966 to 0.1664] when compared to night time release. Conclusions: Our results showed melatonin in mild to moderate depressed patients, not only found lower nighttime levels of serum melatonin, but also found a phase shift in depressed patients.

Day-night variability of water-soluble ions in PM10 samples collected at a traffic site in southeastern Spain

The present work reports diurnal and nocturnal concentrations of water-soluble ions associated to PM10 samples collected during the warm and cold seasons in the urban center of Elche (Southeastern Spain). Statistical differences between daytime and nighttime levels of PM10 were only observed during winter. The lower concentrations during the night were most likely the result of a reduction in traffic-induced road dust resuspension, since nocturnal concentrations of calcium also exhibited a significant decrease compared to daytime levels. During the warm season, nitrate was the only component that showed a statistically significant increase from day to night. The lower nocturnal temperatures that prevent the thermal decomposition of ammonium nitrate and the formation of nitric acid favored by the higher relative humidity at night are the most probable reasons for this variation. The close relationship between nitrate formation and relative humidity during nighttime was supported by the results of the correlation analysis. The reaction of sulfuric and nitric acids with CaCO3 occurred to a greater extent during daytime in summer.

The acoustic environment of inpatient hospital wards in the United Kingdom.

Many hospital noise surveys have shown that patients are subject to high levels of noise, in excess of current World Health Organization guidelines. Much of the previous research has focused on areas perceived to be noisy, such as intensive care units and operating theatres. This paper presents the results of a comprehensive noise survey of five general inpatient hospital wards in the UK. The survey involved continuous noise monitoring over several days, including identification of noise sources, in 31 locations representing a range of typical patient accommodations including single rooms and multi-bed bays, and nurse stations. The results were consistent with those of previous studies with daytime levels ranging from 50 to 61 dB LAeq and nighttime levels from 41 to 51 dB LAeq. Noise levels were not correlated with room/bay size, with single rooms having some of the highest levels. Overall levels were related to reverberation times and to the numbers of high level noise events. Analysis of noise sources showed that much of the noise could be eliminated or reduced through improved design of equipment and ward layouts. In general, noise levels in wards built since the year 2000 were lower than those in the older buildings.

Arterial stiffness in obstructive sleep apnoea: Is there a difference between daytime and night-time?

Obstructive sleep apnoea syndrome (OSAS) is a common chronic systemic disease in the general population, with known associated cardiovascular outcomes. We aimed to investigate arterial stiffness in OSAS patients and compare daytime and night-time values with control subjects. A total of 104 patients undergoing investigation for OSAS with polysomnography also underwent pulse wave velocity (PWV) and augmentation index (AIx) measurements with Mobil-O-Graph for 24 h. Eighty-two patients were found to have OSAS and 22 did not have OSAS and acted as controls. PWV values of the 82 OSAS patients during the 24-h period, both daytime and night-time, were significantly higher than that of the control subjects. Moreover, night-time levels of AIx were significantly higher in OSAS patients than control subjects (P = 0.025). PWV during night-time was higher than daytime measurements in OSAS patients (P = 0.012). Apnoea hypopnoea index (AHI) was significantly correlated with PWV and AIx over 24 h (P = 0.0001, r = 0.412; P = 0.002, r = 0.333, respectively). Positive correlations were also found between oxygen desaturation index (ODI) with PWV and AIx during the night (P = 0.0001, r = 0.480; P = 0.002, r = 0.325, respectively). However, daytime AIx was not significantly correlated with ODI (P = 0.052, r = 0.205). OSAS patients, without known cardiovascular disease, have increased PWV, indicating an increased arterial stiffness, compared with control subjects and correlations between AHI and arterial stiffness indices suggest increased arterial stiffness with increased disease severity. Therefore, arterial stiffness should be considered as a possible cause for cardiovascular complications in OSAS patients.

Fungal spores overwhelm biogenic organic aerosols in a midlatitudinal forest

Abstract. Both primary biological aerosol particles (PBAPs) and oxidation products of biogenic volatile organic compounds (BVOCs) contribute significantly to organic aerosols (OAs) in forested regions. However, little is known about their relative importance in diurnal timescales. Here, we report biomarkers of PBAP and secondary organic aerosols (SOAs) for their diurnal variability in a temperate coniferous forest in Wakayama, Japan. Tracers of fungal spores, trehalose, arabitol and mannitol, showed significantly higher levels in nighttime than daytime (p < 0.05), resulting from the nocturnal sporulation under near-saturated relative humidity. On the contrary, BVOC oxidation products showed higher levels in daytime than nighttime, indicating substantial photochemical SOA formation. Using tracer-based methods, we estimated that fungal spores account for 45 % of organic carbon (OC) in nighttime and 22 % in daytime, whereas BVOC oxidation products account for 15 and 19 %, respectively. To our knowledge, we present for the first time highly time-resolved results that fungal spores overwhelmed BVOC oxidation products in contributing to OA especially in nighttime. This study emphasizes the importance of both PBAPs and SOAs in forming forest organic aerosols.

Natural melatonin fluctuation and its minimally invasive simulation in the zebra finch.

Melatonin is a key hormone in the regulation of circadian rhythms of vertebrates, including songbirds. Understanding diurnal melatonin fluctuations and being able to reverse or simulate natural melatonin levels are critical to investigating the influence of melatonin on various behaviors such as singing in birds. Here we give a detailed overview of natural fluctuations in plasma melatonin concentration throughout the night in the zebra finch. As shown in previous studies, we confirm that “lights off” initiates melatonin production at night in a natural situation. Notably, we find that melatonin levels return to daytime levels as early as two hours prior to the end of the dark-phase in some individuals and 30 min before “lights on” in all animals, suggesting that the presence of light in the morning is not essential for cessation of melatonin production in zebra finches. Thus, the duration of melatonin production seems not to be specified by the length of night and might therefore be less likely to directly couple circadian and annual rhythms. Additionally, we show that natural melatonin levels can be successfully simulated through a combination of light-treatment (daytime levels during subjective night) and the application of melatonin containing skin-cream (nighttime levels during subjective day). Moreover, natural levels and their fluctuation in the transition from day to night can be imitated, enabling the decoupling of the effects of melatonin, for example on neuronal activity, from sleep and circadian rhythmicity. Taken together, our high-resolution profile of natural melatonin levels and manipulation techniques open up new possibilities to answer various melatonin related questions in songbirds.

Importance of epidermal clocks for regulation of hypocotyl elongation through PIF4 and IAA29

Circadian clocks adjust an organism's environmentally relevant physiological responses.. In plants, a decentralized circadian clock system has recently been proposed. Epidermal clock function is crucial for cell elongation; thus, epidermis-specific overexpression of CCA1 caused smaller cotyledons and longer hypocotyls under 27°C, concomitant with elevated night time levels of PIF4 mRNA. However, which tissue's clock regulates PIF4 expression is still an open question. Here we tested spatial expression patterns of PIF4 and its downstream target IAA29 with or without epidermal clock perturbation. Using an epidermal-specific expression system, we revealed that epidermal clock perturbation increases PIF4 expression in both epidermis and mesophyll. However, IAA29 expression is mainly regulated in the epidermis, implying the potential importance of epidermis for regulation of cell elongation through PIF4 and IAA29. We conclude that the circadian clock in epidermis regulates cell elongation mainly in epidermis, and there is also another inter-tissue signaling pathway from epidermis to mesophyll.

Episode-specific drinking-to-cope motivation and next-day stress-reactivity

Background: Research consistently shows drinking-to-cope (DTC) motivation is uniquely associated with drinking-related problems. We furthered this line of research by examining whether DTC motivation is predictive of processes indicative of poor emotion regulation. Specifically, we tested whether nighttime levels of episode-specific DTC motivation, controlling for drinking level, were associated with intensified affective reactions to stress the following day (i.e. stress-reactivity). Design and Methods: We used a micro-longitudinal design to test this hypothesis in two college student samples from demographically distinct institutions: a large, rural state university (N = 1421; 54% female) and an urban historically Black college/university (N = 452; 59% female). Results: In both samples the within-person association between daily stress and negative affect on days following drinking episodes was stronger in the positive direction when previous night's drinking was characterized by relatively higher levels of DTC motivation. We also found evidence among students at the state university that average levels of DTC motivation moderated the daily stress-negative affect association. Conclusions: Findings are consistent with the notion that DTC motivation confers a unique vulnerability that affects processes associated with emotion regulation.

Observational Evidence for Involvement of Nitrate Radicals in Nighttime Oxidation of Mercury.

In the atmosphere, reactive forms of mercury species can be produced by oxidation of the dominant gaseous elemental mercury (GEM). The oxidation of GEM is an important driver for deposition, but oxidation pathways currently are poorly constrained and likely differ among regions. In this study, continuous measurements of atmospheric nitrate radical (NO3) concentrations and mercury speciation (i.e., elemental and reactive, oxidized forms) were performed during a six week period in the urban air shed of Jerusalem, Israel during summer 2012, to investigate the potential nighttime contribution of nitrate radicals to oxidized mercury formation. Average nighttime concentrations of reactive gaseous mercury (RGM) were almost equivalent to daytime levels (25 pg m(-3) and 27 pg m(-3) respectively), in contrast to early morning and evening RGM levels which dropped to low levels (9 and 13 pg m(-3)). During daytime, the presence of RGM was increased when solar radiation exceeded 200 W m(-2), suggesting a photochemical process for daytime RGM formation. Ozone concentrations were largely unrelated to daytime RGM. Nighttime RGM concentrations were relatively high (with a maximum of 97 pg m(-3)) compared to nighttime levels in other urban regions. A strong correlation was observed between nighttime RGM concentrations and nitrate radical concentration (R(2) averaging 0.47), while correlations to other variables were weak (e.g., RH; R(2) = 0.35) or absent (e.g., ozone, wind speed and direction, pollution tracers such as CO or SO2). Detailed analyses suggest that advection processes or tropospheric influences were unlikely to explain the strong nighttime correlations between NO3 and RGM, although these processes may contribute to these relationships. Our observations suggest that NO3 radicals may play a role in RGM formation, possibly due to a direct chemical involvement in GEM oxidation. Since physical data, however, suggest that NO3 unlikely initiates GEM oxidation, NO3 may play a secondary role in GEM oxidation through the addition to an unstable Hg(I) radical species.

Hyperuricaemia is associated with renal damage independently of hypertension and intrarenal renin-angiotensin system activation, as well as their circadian rhythms.

Both hyperuricaemia and activation of the intrarenal renin-angiotensin system (RAS) play an important role in the development of hypertension and renal damage. However, it has not been clear whether hyperuricaemia is associated with renal damage due to hypertension or intrarenal RAS activation, as well as their circadian rhythms. We recruited 43 chronic kidney disease (CKD) patients who did not receive RAS blockers and antihyperuricaemic drugs, and investigated the relationship among serum uric acid (sUA) levels, the circadian rhythm of urinary angiotensinogen (U-AGT) excretion levels, and the levels of albuminuria (U-ACR) and proteinuria (U-P/Cr). sUA levels were significantly associated with estimated glomerular filtration rate (eGFR) (P = 0.002), systolic blood pressure (SBP) (daytime, P = 0.031), and U-ACR (daytime, P = 0.006 and nighttime, P = 0.008) and U-P/Cr (daytime, P = 0.017 and nighttime, P = 0.013). However, there were no significant differences between sUA levels and SBP in nighttime and U-AGT excretion levels in both time periods. Multiple regression analyses for sUA levels were performed using age, sex, eGFR and each parameter (SBP, U-AGT/Cr, U-ACR or U-P/Cr). sUA levels were not associated with SBP or U-AGT/Cr in both time periods. sUA levels tended to correlate with U-P/Cr levels in nighttime, and were significantly associated with U-P/Cr in daytime (P = 0.026) and U-ACR in daytime (P = 0.017) and nighttime (P = 0.046). Moreover, no significant differences were found between sUA levels and night-to-day ratios of some parameters. These data suggest that hyperuricaemia is associated with renal damage, independently of hypertension and intrarenal RAS activation, as well as their circadian rhythms.

Artificial light at night desynchronizes strictly seasonal reproduction in a wild mammal.

Change in day length is an important cue for reproductive activation in seasonally breeding animals to ensure that the timing of greatest maternal investment (e.g. lactation in mammals) coincides with favourable environmental conditions (e.g. peak productivity). However, artificial light at night has the potential to interfere with the perception of such natural cues. Following a 5-year study on two populations of wild marsupial mammals exposed to different night-time levels of anthropogenic light, we show that light pollution in urban environments masks seasonal changes in ambient light cues, suppressing melatonin levels and delaying births in the tammar wallaby. These results highlight a previously unappreciated relationship linking artificial light at night with induced changes in mammalian reproductive physiology, and the potential for larger-scale impacts at the population level.

Daily and annual cycles in thermoregulatory behaviour and cardio-respiratory physiology of black and white tegu lizards.

This study was designed to determine the manner in which metabolism is suppressed during dormancy in black and white tegu lizards (Tupinambis merianae). To this end, heart rate (fH), respiration rate (fR), and deep body temperature (Tb) were continuously monitored in outdoor enclosures by radio-telemetry for nine months. There was a continuous decline in nighttime breathing and heart rate, at constant Tb, throughout the late summer and fall suggestive of an active metabolic suppression that developed progressively at night preceding the entrance into dormancy. During the day, however, the tegus still emerged to bask. In May, when the tegus made a behavioural commitment to dormancy, Tb (day and night) fell to match burrow temperature, accompanied by a further reduction in fH and fR. Tegus, under the conditions of this study, did arouse periodically during dormancy. There was a complex interplay between changes in fH and Tb associated with the direct effects of temperature and the indirect effects of thermoregulation, activity, and changes in metabolism. This interplay gave rise to a daily hysteresis in the fH/Tb relationship reflective of the physiological changes associated with warming and cooling as preferred Tb alternated between daytime and nighttime levels. The shape of the hysteresis curve varied with season along with changes in metabolic state and daytime and nighttime body temperature preferences.

Spring and summer night-time high ozone episodes in the upper Brahmaputra valley of North East India and their association with lightning

Simultaneous and round the clock measurement during thunderstorm and lightning has been used to study the impact of lightning generated NOx (LNOx) on O3 mixing ratio within the boundary layer during night-time. Lightning flash rate obtained from Lightning Image Sensor (LIS) on board TRMM over the Brahmaputra valley centred around Dibrugarh has been used to identify the events in which NOx was elevated with simultaneous dip in O3 for a short duration followed by subsequent elevation of O3 in spring and summer of 2012–2014. Seasonally averaged O3 attains higher values at night on thunderstorm days as compared to that on clear and cloudy days both in spring and summer i.e. as against a minimum night-time (1700–0500 h) values of ∼3 ppb on clear days, the mean night-time level on thunderstorm days is ∼18 ppb in spring and ∼12 ppb in summer. The estimated steady state O3 concentration is well correlated with the NO2/NO ratio and found to be ∼33% of the measured O3. One day isentropic concentration weighted trajectory (CWT) analysis carried out for the spring and summer seasons reveal that part of GWB and Bangladesh are the potential additional source of O3 in both the seasons. LNOx is found to contribute to ∼33% of the measured O3 during the study period. Enhancement of O3 is well correlated with the lightning radiance indicating direct photodissociation of O3 due to lightning. ΔO3 is independent of the location of the flash rather depends on flash intensity.

Measuring ambient particulate matter in three cities in Cameroon, Africa

This is the first study of particulate matter (PM) air pollution in Cameroon. In this study, mass concentration and PM size fractions as well as carbonaceous contribution to PM are measured in Bafoussam, Bamenda, and Yaoundé, Cameroon. Average concentrations in Bafoussam, Bamenda, and Yaoundé of PM2.5 are 67 ± 14, 132 ± 64, and 49 ± 12 μg/m3 and PM10 are 105 ± 29, 141 ± 107, and 65 ± 21 μg/m3, respectively. Daytime levels of PM2.5 and PM10 are seen to be higher than nighttime levels in all cities except Bamenda where nighttime levels are higher for both PM sizes. In Bafoussam, the average PM1.0 particle number concentration during the day is 19,800 pt/cc and during the evening is 15,200 pt/cc. PM2.5/PM10 mass ratios are 0.65 ± 0.05, 0.75 ± 0.05, and 0.78 ± 0.09 for Bafoussam, Bamenda, and Yaounde, respectively. Elemental carbon (EC) and organic carbon (OC) contribution to PM2.5 in Bafoussam, Bamenda, and Yaoundé are 3.9%, 2.9% and 12% for EC and 17.7%, 23.6%, and 34.2% for OC, respectively. After conducting spatial variability of PM mass concentration and size fractionation sampling at various locations within each of the three cities, we find that PM2.5 averages are highest during commercial meal preparation in Bafoussam (684 ± 546 μg/m3), and on the road in Bamenda (417 ± 113 μg/m3) and Yaoundé (110 ± 57 μg/m3). Additional air quality research in Central and West Africa is necessary to begin implementing policy steps that influence change and to advocate for improved health conditions in this rapidly expanding region of the world.

Factors affecting sleep in the critically ill: An observational study

PurposeThe aims of the current study were to describe the extrinsic and intrinsic factors affecting sleep in critically ill patients and to examine potential relationships with sleep quality. Materials and MethodsSleep was recorded using polysomnography (PSG) and self-reports collected in adult patients in intensive care. Sound and illuminance levels were recorded during sleep recording. Objective sleep quality was quantified using total sleep time divided by the number of sleep periods (PSG sleep period time ratio). A regression model was specified using the “PSG sleep period time ratio” as a dependent variable. ResultsSleep was highly fragmented. Patients rated noise and light as the most sleep disruptive. Continuous equivalent sound levels were 56 dB (A). Median daytime illuminance level was 74 lux, and nighttime levels were 1 lux. The regression model explained 25% of the variance in sleep quality (P = .027); the presence of an artificial airway was the only statistically significant predictor in the model (P = .007). ConclusionsThe presence of an artificial airway during sleep monitoring was the only significant predictor in the regression model and may suggest that although potentially uncomfortable, an artificial airway may actually promote sleep. This requires further investigation.

Su2063 There Is No Relationship Between the Fructose Transporter, GLUT5 and GLUT2, Protein or mRNA Expression Levels in Irritable Bowel Syndrome With Fructose Malabsorption and Intolerance

Purpose: Poor sleep is commonly reported by patients with IBS. When stressed prior to bedtime patients with IBS show dysregulation of the pituitary-adrenal axis during sleep. Evidence suggests the tryptophan (TRP) metabolic pathways are also altered in patients with IBS. Our purpose was to determine whether alterations in TRP metabolism may be linked to cortisol in women with and without IBS. Methods: Women, ages 18-45, (n=46 IBS [Rome III]; controls [C; n=24]) were studied in a sleep laboratory and serum samples obtained on the third night following the introduction of a social stressor (anticipation of public speaking). Samples were obtained 2 hours following sleep onset (time 1) and 1 hour prior to awakening (time 2). All subjects completed a demographic data sheet, Rome III Diagnostic Questionnaire for Functional GI Disorders, Pittsburgh Quality Sleep Index (PSQI) and 28-day symptom diaries. Serum cortisol levels were determined by ELISA and metabolite levels by targeted liquid chromatography-mass spectrometry (LC-MS). Results: More women with IBS reported symptoms of insomnia (PSQI) as compared to C group (40% versus 24%) and reduced sleep efficiency by polysomnography (p<0.05). As reported previously cortisol/ACTH ratios were higher in IBS as compared to C women. Of the 6 kyneurinine pathway metabolites (primary TRP metabolic route) only niacinamide was significantly higher in women with IBS. However, 5-hydroxytryptophan levels were higher (p<.052) in women with IBS. None of the 3 methylation metabolites were significantly different between IBS and Cs. When ratios of metabolites were calculated significant differences were observed as shown in Table 1. Significant negative correlations between cortisol/ACTH and 5-hydroxytryptophan, methionine, kyneurinine, and betaine were found at one or both time points. TRP levels were significantly correlated with sleep quality (diary) in the IBS group. Conclusion: Nighttime levels of cortisol/ACTH are associated with metabolites in the TRP metabolic pathway particularly those associated with methylation. Whether these associations fully account for the frequent reports of poor sleep in women with IBS requires further study. Table 1

Light-enhanced primary marine aerosol production from biologically productive seawater

Physical and biogeochemical processes in seawater controlling primary marine aerosol (PMA) production and composition are poorly understood and associated with large uncertainties in estimated fluxes into the atmosphere. PMA production was investigated in the biologically productive NE Pacific Ocean and in biologically productive and oligotrophic regions of the NW Atlantic Ocean. Physicochemical properties of model PMA, produced by aeration of fresh seawater under controlled conditions, were quantified. Diel variability in model PMA mass and number fluxes was observed in biologically productive waters, increasing following sunrise and decreasing to predawn levels overnight. Such variability was not seen in oligotrophic waters. During daytime, surfactant scavenging by aeration in the aerosol generator without replenishing the seawater in the reservoir reduced the model PMA production in productive waters to nighttime levels but had no influence on production from oligotrophic waters. Results suggest bubble plume interactions with sunlight-mediated biogenic surfactants in productive seawater significantly enhanced model PMA production.