Air CO2 Levels Research Articles

Digital Technology, Education, and Economic Growth in a Green Economy in Indonesia

This study investigates digital inclusion in the form of internet users, education, economic growth, and CO2 emissions to understand the digital economy and green economy in Indonesia. This research examines data from 2000 until 2020 to be able to produce "autoregressive vectors" that may be used to evaluate the causal link between variables. Based on secondary data from the World Bank, the following multivariate regression model was used to investigate the causal link between Internet Users, Economic Growth, Education, and Carbon dioxide expenditure in Indonesia. Carbon Dioxide encourages investment in Education to solve environmental problems so that the higher levels of CO2 in Indonesia's air encourage the Indonesian government to invest in education in terms of CO2 problems. Where education itself significantly increases public awareness so the relationship between education and CO2 has a significant negative correlation. And education drives future education and significantly boosts economic growth. High economic growth or a more established economy actually has a significant negative correlation with CO2 levels, which means that a green economy can be applied in Indonesia. The interesting thing is that there is a significant positive relationship between internet users and the increase in CO2 levels in the air in Indonesia. This is very interesting because the use of the internet in Indonesia has an impact on the business sector and ordering or online shopping increases the use of transportation for shipping goods which actually increases CO2 levels in Indonesia's air.

Review of the assumption of ideal mixed ventilation and estimation of attendances at trade fairs in exhibition halls

During the SARS-CoV-2 pandemic, large-scale events were initially suspended categorically without consideration of ventilation technology. In this study, CO2 concentrations were measured during three trade fairs in the fall of 2021 at Messe Frankfurt with the aim of assessing air mixing and dilution of loads emitted through human respiration. 24 sensors were installed on columns near aisles, in peripheral areas and exhaust/ambient air ducts. At three positions, in addition to a height of 2 m, measurements were taken at 3.2 m height to reveal potential stratification effects. Finally, attendances were estimated based on exhaust/ambient air CO2 levels and ambient air volume flows. Results show that the maximum CO2 concentration during visiting hours never exceeded 835 ppm. Indoor air quality thus qualified as hygienically insignificant at all times. Furthermore, no stratification was detected, indicating that air was mixed well without apparent local accumulations of CO2 and thus potentially infectious aerosols within the breathing zone. Estimated mean attendance corresponds to information provided by Messe Frankfurt. Finally, results indicate that the exhaust CO2 concentration represents a good indicator to assess air quality within the occupied zone in large-scale halls, making elaborate measurements within the occupied zone obsolete. Further evaluation is needed to support this.

Membrane Processes for Direct Carbon Dioxide Capture From Air: Possibilities and Limitations

The direct capture of CO2 from air (DAC) has been shown a growing interest for the mitigation of greenhouse gases but remains controversial among the engineering community. The high dilution level of CO2 in air (0.04%) indeed increases the energy requirement and cost of the process compared to carbon capture from flue gases (with CO2 concentrations around 15% for coal power plants). Until now, solid sorbents (functionalized silica, ion exchange resins, metal–organic frameworks, etc.) have been proposed to achieve DAC, with a few large-scale demonstration units. Gas-liquid absorption in alkaline solutions is also explored. Besides adsorption and absorption, membrane processes are another key gas separation technology but have not been investigated for DAC yet. The objective of this study is to explore the separation performances of a membrane unit for CO2 capture from air through a generic engineering approach. The role of membrane material performances and the impact of the operating conditions of the process on energy requirement and module production capacity are investigated. Membranes are shown to require a high selectivity in order to achieve purity in no more than two stages. The specific energy requirement is globally higher than that of the adsorption and absorption processes, together with higher productivity levels. Guidelines on the possibilities and limitations of membranes for DAC are finally proposed.

Demonstration of Electrochemically-Driven CO2 Separation Using Hydroxide Exchange Membranes

Hydroxide exchange membrane fuel cells (HEMFCs) are a potentially lower-cost hydrogen fuel cell technology; however, ambient levels of CO2 in air significantly reduce HEMFCs’ performance. In this work, we demonstrate an electrochemically-driven CO2 separator (EDCS) which can be used to remove ambient levels of CO2 from air upstream of the HEMFC stack in fuel cell vehicles, protecting it from CO2-related performance losses. The EDCS operating window was explored for current density, anode flow, and cathode flow with respect to its impact on CO2 separation performance. Additionally, gas-phase mass transport was improved by selecting flow fields and gas diffusion layers conducive to the EDCS operating regime. The use of a carbon-ionomer interlayer at the cathode was explored and improved CO2 removal performance from 77.7% to 98.2% at 20 mA cm−2. An analytical, 1-D model is used to explain the experimental observations and design improvements. A single-cell, 25 cm2 EDCS using the aforementioned improved design demonstrated greater than 98% CO2 removal at a cathode flow rate of 1300 sccm for 100 h with 2.7% hydrogen stack consumption.

Development of Electrochemically-Driven CO2 Separator for Hydroxide Exchange Membrane Fuel Cells in Transportation Applications

Hydrogen fuel cell vehicles are a promising, emerging alternative to the internal combustion engine but the commercialized proton exchange membrane fuel cells (PEMFCs) are comparatively expensive. Hydroxide exchange membrane fuel cells (HEMFCs) are a potentially lower cost hydrogen fuel cell technology under development; unfortunately, ambient levels of CO2 in air reduce HEMFC performance and impede HEMFCs from becoming competitive with the incumbent fuel cell technology.1 Current levels of atmospheric CO2 have been shown to decrease fuel cell performance up to 200 mV.2 The hydroxide produced during the electrochemical reaction in a HEMFC reacts readily with CO2 in air at the cathode due to its acid-base reaction and transports CO2 across the hydroxide exchange membrane. At the anode, the bicarbonates build up lowering the local pH until CO2 evolution is favorable, concurrently the pH gradient saps cell voltage. However, this transport results in the effective separation of CO2 from air. By optimizing a HEMFC for CO2 capture, rather than power production, an electrochemically-driven CO2 separator (EDCS) was developed using a poly(aryl piperidinium) membrane.3 The continuous and compact EDCS has the potential to enable HEMFCs to operate efficiently with ambient air in automotive applications.This work will demonstrate the ability of the EDCS to effectively and continuously remove CO2 from air at ambient levels using minimal hydrogen flow to power the separation. This work will explore the effect of operating conditions such as flow rates, current density, and relative humidity on CO2 separation performance with the innovative EDCS. A carbon-ionomer interlayer between the catalyst layer and membrane was added to improve CO2 capture by creating an accessible volume for hydroxide and CO2 gas to react. Additionally, various design features of the cell were investigated to improve the mass transport such as flow fields and gas diffusion layers. The CO2 removal performance of a single-cell 25 cm2 EDCS is shown in Figure 1. Currently, the optimal design configuration of the EDCS has achieved 98% CO2 removal for 100 hours (Figure 2) with the potential to improve CO2 removal as well as processed gas throughput by further development of the module’s design.

Simulated global increases in atmospheric CO2 alter the tissue composition, but not the growth of some submerged aquatic plant bicarbonate users growing in DIC rich waters

Current global change scenarios predict an increase in atmospheric CO2 from the current 380 ppm to a value ranging from 540 ppm to 960 ppm by the year 2100. The effects of three air CO2 levels (400, 600 and 800 ppm) on five submerged aquatic plants that utilize HCO3− were studied, using the elevated CO2 Open Top Chamber facility at Rhodes University (Grahamstown, South Africa). Plants grew in water with two different initial dissolved inorganic carbon (DIC) concentrations of 1.5 and 3.0 mM. Overall, the growth rates and biomass allocation to roots were not affected by the initial DIC and air CO2, even though differences between the species were found. Furthermore, no overall effects were found on net photosynthesis, chlorophyll and starch content, even though significant effects of CO2 and DIC were observed in some species. In contrast, with increasing DIC and air CO2 a significant global decline in leaf nitrogen content linked with an increased C:N molar ratio was observed. The results indicate that submerged aquatic HCO3− users will be less affected by atmospheric CO2 increases when growing in DIC rich waters, in comparison to obligate CO2 users growing under CO2 limiting conditions as documented in previous studies. However, the changes found in plant nitrogen illustrate that atmospheric CO2 increases will affect nitrogen absorption by submerged plants, with subsequent ecosystem level effects.

The use of modern technologies in carbon dioxide monitoring

Abstract Indoor environment has huge influence on person’s health and overall comfort. It is of great importance that we realize how essential indoor air quality is, considering we spend on average as much as 90% of our time indoors. There are many factors that affect indoor air quality: specifically, inside air temperature, relative humidity, and odors to name the most important factors. One of the key factors indicating indoor air quality is carbon dioxide (CO2) level. The CO2 levels, measured in prefab apartment buildings, indicates substantial indoor air quality issues. Therefore, a proper education of the occupants is of utmost importance. Also, great care should be directed towards technical and technological solutions that would ensure meeting the normative indoor environment criteria, especially indoor air CO2 levels. Thanks to the implementation of new emerging autonomous technologies, such as Internet of Things (IoT), monitoring in real-time is enhanced. An area where IoT plays a major role is in the monitoring of indoor environment. IoT technology (e.g. smart meters and sensors) provide awareness of information about the quality of indoor environment. There is a huge potential for influencing behaviour of the users. Through the web application, it is possible to educate people and ensure fresh air supply.

Elevated atmospheric CO2 enhances grazer‐induced morphological defense in the freshwater green alga Scenedesmus obliquus

AbstractAtmospheric CO2 level is increasing and considerably influences aquatic ecosystems. Grazer‐induced defenses in phytoplankton stabilize the structures of aquatic food webs. Costs associated with defense have resulted in a situation in which the effectiveness of inducible defenses depends on environmental conditions. To investigate the grazer‐induced defense responses to elevated air CO2 levels, the algae Scenedesmus obliquus was cultured under two air CO2 concentrations (390 ppm and 750 ppm) in the absence or presence of predator‐derived cues (Daphnia filtrate). In response to Daphnia filtrate, colonial populations such as eight‐celled colony were largely formed in S. obliquus. When air CO2 was elevated to 750 ppm, the inorganic carbon contents in media increased, thereby stimulating algal reproduction and photosynthesis. Moreover, the volumes of unicells and two‐celled colonies were enlarged under elevated CO2 conditions. These physiological changes satisfied the material and energy demands for the formation of larger colonies. Based on the consistent surface area per volume of the large colony under ambient and elevated CO2 conditions, the increased inorganic carbon (by CO2 enrichment) facilitated the carbon uptake of the multi‐celled colony. Thus, the morphological defense in phytoplankton was enhanced with more eight‐celled colonies formed in populations grown in a high‐CO2 environment. The present result verified the hypothesis that inducible defense is less costly and has higher effectiveness with increasing carbon availability. The enhancement of anti‐grazer morphological defenses in phytoplankton potentially alters the trophic cascades between phytoplankton and zooplankton and contributes to the redirected energy and nutrient flow in ecosystem‐level processes under a CO2‐rising climate.

Comparative susceptibility of Corcyra cephalonica (Lepidoptera: Pyralidae) eggs to carbon dioxide and nitrogen at different temperatures

The aim of this study was to evaluate the susceptibility of the egg stage of the rice moth Corcyra cephalonica to modified atmospheres (MAs) enriched with CO2 or N2 at 25, 30 and 35 °C combined with various exposure times. The tested modified atmospheres containing CO2 were 20% CO2, 16% O2 and 64% N2; 40% CO2, 12% O2 and 48% N2; 60% CO2, 8% O2 and 32% N2 and 80% CO2, 4% O2 and 16% N2. The tested modified atmospheres containing N2 were 97% N2 and 3% O2 and 98% N2 and 2% O2. The results showed that the hatchability responding to modified atmospheres enriched with either CO2 or N2 decreased significantly with an increase in exposure time, gas content (%) and temperature. All tested combinations provided complete (100%) egg control in less than 4 days. Based on 100% mortality, shorter exposures were obtained with 80% CO2 than with N2 at most tested temperatures. The modified atmospheres enriched with 98% N2 were more effective than 97% N2 against C. cephalonica eggs, especially at 35 °C. It is recommended to use high levels of CO2 in air (80%) and N2 (98%) in controlling 0–24-h-eggs of C. cephalonica within 24–36 h for CO2 and 18–72 h for N2.

Cave ventilation and rainfall signals in dripwater in a monsoonal setting – a monitoring study from NE India

Detailed monitoring of subterranean microclimatic and hydrological conditions can delineate factors influencing speleothem-based climate proxy data and helps in their interpretation. Multi-annual monitoring of water stable isotopes, air temperature, relative humidity, drip rates and PCO2 in surface, soil and cave air gives detailed insight into dripwater isotopes, temperature and ventilation dynamics in Mawmluh Cave, NE India.Water isotopes vary seasonally in response to monsoonal rainfall. Most negative values are observed during late Indian Summer Monsoon (ISM), with a less than one-month lag between ISM rainfall and drip response. Two dry season and two less-well distinguishable wet season dynamic ventilation regimes are identified in Mawmluh Cave. Cave air temperatures higher than surface air result in chimney ventilation during dry season nights. Dry season days show reduced ventilation due to cool cave air relative to surface air and cold-air lake development. Both, high water flow and cooler-than-surface cave air temperatures result in air inflow during wet season nights. Wet season daytime ventilation is governed by river flow, but is prone to stagnation and development of cold air lakes. CO2 monitoring indicates that PCO2 levels vary at diurnal to annual scale. Mawmluh Cave seems to act as CO2 sink during part of the dry season. While very likely, additional data is needed to establish whether wet season cave air CO2 levels rise above atmospheric values. Drip behavior is highly nonlinear, related to effective recharge dynamics, and further complicated by human influence on the epikarst aquifer.

Eco-Friendly Houses: Green Future Ahead

“April 2014 average CO2 value was 401.33 ppm in air, the first monthly average over 400 ppm in human history” – tweeted the Scripps Institution of Oceanography in San Diego, US on 1 May 2014. The tweet was indeed alarming as the 400 parts per million (ppm) CO2 level in air was exceeded for the very first time in 800,000 years. The constant rise in the levels of greenhouse gases viz. CO2, CH4, N2O, O3 and CFCs has led to global warming and many other environmental adversities necessitating immediate mitigation of climate change. It is observed that the last decade between years 2000-2010 caused more damage than any of the previous eras. This decade led to the rise of 0.850C of combined ocean and land temperature, rising sea levels, diminishing snow and ice sheets, shrinking glaciers, shifting seasons, ocean acidification and affecting food productivity.

Between Scylla and Charybdis: energy, carbon dioxide, and indoor environmental quality

Between Scylla and Charybdis: energy, carbon dioxide, and indoor environmental quality

Differences between rice and wheat in RuBP regeneration capacity per unit of leaf nitrogen content

Light-saturated photosynthesis in air CO2 levels for a given leaf-N content is higher in wheat than in rice. This is caused by a greater Rubisco capacity in wheat (Makino et al., 1988, Planta 174, 30-38). In this study, we found that CO2-saturated photosynthesis is also higher in wheat than in rice. This means that RuBP regeneration capacity is also greater in wheat. Therefore, we examined the biochemical factor(s) for differences in RuBP regeneration capacity between rice and wheat. Insoluble-N, soluble protein-N, and TCA soluble-N contents did not differ between the two species. The activities of several Calvin cycle enzymes such as Rubisco, NADP-triosephosphate dehydrogenase, phosphoglycerate kinase and choroplastic fructosebisphosphatase activities per unit of leaf nitrogen were all higher in wheat than in rice. Although sucrose-phosphate synthase (SPS) is a key enzyme during Pi regeneration, the Vmax activity for UDP-G was almost the same between the two species and its Km value was a little lower in rice. Chl content and Chl a/b ratio did not differ. Cytochrome (Cyt) f content was greater in wheat than in rice, whereas coupling factor 1 content was greater in rice. Among them, Cyt f content was most highly correlated with CO2-saturated photosynthesis, irrespective of the two species. In addition, the regression line between Cyt f content and CO2-saturated photosynthesis in both species fell on the same line. The results, thus, suggest that higher RuBP regeneration capacity in wheat leaves is caused by a greater Cyt f content.

Gas Exchange Characteristics in Leaves of the Euphorbiacea Aleurites montana as Consequence of Growth under 700 ppm CO2 in Air A Study on Photosynthesis and Photorespiration in the Chinese Tung-Oil Tree

Abstract Three months old plants of the Chinese tung-oil tree Aleurites montana (Euphorbiaceae) were cultivated for 4 months in air containing 700 ppm CO2. These plants, which grow substantially better in the CO2-enriched atmosphere, were analyzed by mass spectrometry for photosynthesis and photorespiration together with control plants grown all the time in normal (350 ppm CO2) air. Thereafter part of the plants was subjected for two weeks to 0.3 ppm SO2 in the atmosphere and again analyzed for photosynthesis and photorespiration. Aleurites montana exhibits a strongly CO2-dependent photosynthesis which partially explains the observed stimulatory effect of 700 ppm CO2 on growth of the plant. In control plants grown in normal air, photorespiration measured simultaneously with photosynthesis via the uptake of l80 2 in the light, is much lower than in C3-plants like tobacco (H e et al., 1995, Z. Naturforsch. 50c, 781-788 ). In Aleurites grown in 700 ppm CO2, however, photorespiration is completely absent in contrast to tobacco when grown under 700 ppm CO2. In tobacco, photorespiration is not inhibited to the extent of the in vitro experiments in which plants grown at 350 ppm CO2 are measured under the increased CO2 content of 700 ppm. Gas exchange measurements carried out by mass spectrometry show that the ratio of O2 evolved to CO2 fixed is about 0.5. Apparently, part of the CO2 fixed is channelled into a metabolic path without concomitant O2-evolution. Although the plant has no succulent appearance (its leaves somehow resemble maple leaves) apparently a Crassulacean type metabolism is performed. When Aleurites plants grown all the time in normal air with 350 ppm, are exposed for two weeks to 0.3 ppm SO2 the treatment completely inhibits this CO2-fixing portion which is tentatively attributed to a Crassulacean type of metabolism. This is demonstrated by a normal C3-type ratio O2 evolved /CO2 fixed of 1. When Aleurites plants, grown for 4 months in a CO2-enriched atmosphere of 700 ppm CO2, are subjected for two weeks to 0.3 ppm SO2, the features of control plants show up again. When these plants are tested under 350 ppm CO2 the Crassulacean type CO2-fixation apparently is not inhibited by SO2. Photorespiration, although low, is present in the same activity as in the controls. Seemingly, an increased level of CO2 in air tends to alleviate the impact of the SO2 at least in the Chinese tung-oil tree.

Ethanol Accumulation as an Indicator of Sensitivity of Different Horticultural Produce to 30% CO2 in Air Storage at 7C

Controlled atmospheres (CA) have been used as auxiliary to refrigeration for the storage and transportation of food crops. Commodities sensitive to high levels of CO2 experience fermentation. This study was focused upon the effects of CO2-enriched atmospheres on ethanol (ETOH) accumulation as an indicator of the sensitivity of 22 different produce to short-term exposure to 30% CO2 in air for 2 days at 7C. Commodities were obtained from a wholesale or grocer supermarket. ETOH was determined by gas chromatography (GC). Differences in response to 30% CO2 in air were observed among commodities. Kiwi fruit and broccoli had initial low levels of ETOH, which greatly increased after the first day of storage. Cherries and spinach maintained approximately a constant increase in ETOH accumulation during the whole period of storage. Pickling cucumber and zucchini squash had high ETOH accumulation at the early period of storage, which was even higher by the second day of exposure to 30% CO2 in air. In most of the commodities under study ETOH accumulation increased as a response to 30% CO2 levels in air. There was no apparent influence of plant organ on ETOH accumulation.

Numerical Experiments o Possible Changes in Maize Canopy Climate due to Increasing CO2 Levels

The sensitivity of canopy climate to the air's CO2 level increment is investigated using a canopy flow model based on the mean turbulent field (MTF) closure models. Leaf processes in the model are highly parametrized using the experimental results obtained from the dependence of stomatal diffusion resistance on the CO2 level. An increase in stomatal resistance with the CO2-level was greater in C4 plants (maize) than in C3 plants (rice), indicating that changes in maize canopy climate are more significant than in rice canopy. In a model maize canopy, daily sensible heat loss increased along with CO2 levels, with concomitant decreases in daily latentheatloss. Somewhat hotter and drier air conditions within maize canopies at higher CO2-level are anticipated to be unfavorable for the growth and yield of maize crops.

Measurement of Photosynthetic Gas Exchange in Controlled Environments

Early controlled-environment research used growth chambers primarily as “photoperiod rooms” to study effects of environment on long-term plant developmental processes (Downs and Hellmers, 1975). More recently, growth dynamics analysis has been used to measure photosynthetic productivity of crop canopies or individual plants in controlled environments over periods of only a few days (Knight and Mitchell, 1983). However, as the emphasis of controlled-environment research shifts toward definition of optimum growth conditions (Hoff et al., 1982), there will be increasing demand to measure instantaneous photosynthetic response within modified controlled environments. Net photosynthesis and respiration are measured most conveniently as CO2 consumption or evolution, respectively, by a given area or mass of plant tissue over a defined period. At ≈ 3 5 0 μmol·mol –1(μl·liter –1, vpm), CO2 is a trace gas compared to the major components of air (N2, O2, H2Ov). As such, CO2 is detectable to 1 μmol·mol –1 by thermal conductivity gas chromatography (TCD-GC) or infrared gas analysis. The infrared gas analyzer (IRGA) is amenable to continuous-flow monitoring of the CO2 level in air and will detect near-real-time changes in gas-exchange rate by plants as environmental conditions vary. Modem electronic detector systems permit a degree of miniaturization of IRGAs that allows their portability into growth chambers as well as to the field. Gas exchange by chamber-grown plants may be measured for individual attached leaves, entire shoots, or leaf canopies of multiple plants. Various plant enclosure techniques are used for each type of measurement. Because a limited number of off-the-shelf assimilation chambers are available on the commercial market, many researchers have developed their own cuvettes for specific applications. Assimilation chambers often are constructed from transparent acrylic (plexiglass) or polycarbonate (mylar) plastic. Because these plastics adsorb water vapor (H2Ov) and, consequently, CO2

The 5'-flanking region of the gene encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase is crucial for growth of the cyanobacterium Synechococcus sp. strain PCC 7942 at the level of CO2 in air

Transformation of the high-CO2-requiring mutants (hcr) O221 and E1 derived from the cyanobacterium Synechococcus sp. strain PCC 7942 by a wild-type DNA library restored their ability to grow at the level of CO2 in air. A plasmid (pE12) containing a 10-kilobase DNA insert was rescued from a O221 heterogenote and proved to transform both O221 and E1 to the wild-type phenotype. The capacity of the pE12 subclones to confer the wild-type phenotype to O221 transformants enabled the mapping of the mutation in O221 (designated hcrO221) within a 232-base-pair PstI-BstXI DNA restriction fragment. Sequence analysis revealed two open reading frames (ORFs) at positions -1745 to -1262 (ORFI) and -1218 to -393 (ORFII) upstream of the rbcL gene. A 3-kilobase PstI fragment of O221 was cloned, and hcrO221 was found to be a point mutation within the PstI-BstXI region -1309 nucleotides upstream of the rbcL gene. The significance of this flanking region for adaptation to air levels of CO2 was further demonstrated by the generation of new hcr mutants following insertional inactivation of wild-type DNA in the BstXI site. Electron microscopy revealed aberrant carboxysome structures in growing cells of the hcr mutants, a defect that was possibly related to the mutation, since transformation with pE12 derivatives restored the carboxysome structure to normal.

Characteristics of lung mechanoreceptors in spotted gar, Lepisosteus oculatus.

Single unit and whole nerve activity were recorded in situ from pulmonary mechanoreceptors in Lepisosteus oculatus in response to step inflation and ramp or flow through ventilation of the lung with air and varying levels of CO2 in air. Slowly adapting receptors (SAR), rapidly adapting receptors (RAR), and CO2-sensitive SAR were identified. Whole nerve activity was often present when transpulmonary pressure was 0 cmH2O and increased due to recruitment and elevated discharge of already-active fibers as lung volume rose. SAR became tonically active once the lung exceeded their threshold volume and demonstrated a rate-sensitive burst of activity on inflation and a rate-sensitive inhibition of activity after deflation of the lung. RAR responded to lung inflation or deflation with a burst of activity. Six of eleven SAR were inhibited by ventilation of the lung with from 6 to 10% CO2 in air, even when lung pressure and volume were kept constant. These receptor discharge characteristics, which were similar to those found for lungfish and amphibians, may account for the reflex responses of gar to lung volume changes.

Prevention of Mold Growth and Toxin Production through Control of Environmental Conditions

Environmental conditions influence mold growth and mycotoxin production. Such things as water activity (aw), temperature, pH and atmosphere can strongly affect and profoundly alter patterns of growth and mycotoxin production. Generally, maintenance of low temperatures will prevent aflatoxin production in stored products, whereas other toxins such as penicillic acid, patulin, zearolenone and T-2 toxin may be produced at low temperatures. Toxic Penicillium and Fusarium species are generally more capable of growth at low temperatures than are toxic species of Aspergillus. Temperature interacts with aw to influence mold growth and mycotoxin production. Aflatoxin B1 can be produced at conditions of aw and temperature which are close to the minimum aw and temperature for growth. On the other hand, patulin, penicillic acid and ochratoxin A are produced within a narrower range of aw and temperature, compared with those for growth. In fact, production of patulin and penicillic acid by Penicillium species appears to be confined to high aw values only. In optimal substrates, the minima of aw and temperature for growth and toxin production may be lower than in other substrates. It appears that pH and substrate composition have no great effect on growth of toxic molds, but may have a great influence on toxin production. Presence of CO2 and O2 influences mold growth and mycotoxin production. A 20% level of CO2 in air depresses aflatoxin production and markedly depresses mold growth. Decreasing the O2 concentration of air to 10% depresses aflatoxin production, but only at O2 levels of less than 1% are growth and aflatoxin production completely inhibited. With patulin- and sterigmatocystin-producing molds, concentrations of 40% CO2 depress growth and toxin production, but a level of 90% CO2 is needed to completely inhibit production of these toxins. Decreasing O2 concentration to 2% depresses production of patulin and sterigmatocystin but does not affect fungal growth. Only at levels down to 0.2% are growth and toxin production completely inhibited. Controlled atmospheres with increased CO2 (above 10%) and decreased O2 (2%) can be used to retard mold growth. Exclusion of O2 by vacuum packaging in materials with low O2 permeability will depress or even prevent aflatoxin production. Presence of other microorganisms may also restrict fungal growth and mycotoxin production. Aflatoxin production by Aspergillus flavus in mixed cultures with Aspergillus niger is less than in pure culture. Mixtures of fungi growing in grains and nuts in competition with A. flavus seem to prevent aflatoxin production. Other organisms including Rhizopus nigricans, Saccharomyces cerevisiae, Brevibacterium linens and some lactic acid bacteria have been shown to reduce growth and aflatoxin production by Aspergillus parasiticus. In general, mold growth and mycotoxin production can be prevented by employing various measures based on knowledge of the factors involved. Choice of the measures depends upon the type of product, storage period and available techniques.