Source apportionment for indoor air pollution: Current challenges and future directions

Source apportionment (SA) for indoor air pollution is challenging due to the multiplicity and high variability of indoor sources, the complex physical and chemical processes that act as primary sources, sinks and sources of precursors that lead to secondary formation, and the interconnection with the outdoor environment. While the major indoor sources have been recognized, there is still a need for understanding the contribution of indoor versus outdoor-generated pollutants penetrating indoors, and how SA is influenced by the complex processes that occur in indoor environments. This paper reviews our current understanding of SA, through reviewing information on the SA techniques used, the targeted pollutants that have been studied to date, and their source apportionment, along with limitations or knowledge gaps in this research field. The majority (78 %) of SA studies to date focused on PM chemical composition/size distribution, with fewer studies covering organic compounds such as ketones, carbonyls and aldehydes. Regarding the SA method used, the majority of studies have used Positive Matrix Factorization (31 %), Principal Component Analysis (26 %) and Chemical Mass Balance (7 %) receptor models. The indoor PM sources identified to date include building materials and furniture emissions, indoor combustion-related sources, cooking-related sources, resuspension, cleaning and consumer products emissions, secondary-generated pollutants indoors and other products and activity-related emissions. The outdoor environment contribution to the measured pollutant indoors varies considerably (<10 %- 90 %) among the studies. Future challenges for this research area include the need for optimization of indoor air quality monitoring and data selection as well as the incorporation of physical and chemical processes in indoor air into source apportionment methodology.

Formation of indoor nitrous acid (HONO) by light-induced NO2 heterogeneous reactions with white wall paint

Gaseous nitrogen dioxide (NO2) represents an oxidant that is present in relatively high concentrations in various indoor settings. Remarkably increased NO2 levels up to 1.5 ppm are associated with homes using gas stoves. The heterogeneous reactions of NO2 with adsorbed water on surfaces lead to the generation of nitrous acid (HONO). Here, we present a HONO source induced by heterogeneous reactions of NO2 with selected indoor paint surfaces in the presence of light (300 nm<λ<400 nm). We demonstrate that the formation of HONO is much more pronounced at elevated relative humidity. In the presence of light (5.5 W m(-2)), an increase of HONO production rate of up to 8.6·10(9) molecules cm(-2) s(-1) was observed at [NO2]=60 ppb and 50% relative humidity (RH). At higher light intensity of 10.6 (W m(-2)), the HONO production rate increased to 2.1·10(10) molecules cm(-2) s(-1). A high NO2 to HONO conversion yield of up to 84% was observed. This result strongly suggests that a light-driven process of indoor HONO production is operational. This work highlights the potential of paint surfaces to generate HONO within indoor environments by light-induced NO2 heterogeneous reactions.

Atmospheric photosensitized heterogeneous and multiphase reactions: from outdoors to indoors

This proposal involves direct photolysis processes occurring in the troposphere incorporating photochemical excitation and intermolecular energy transfer. The study of such processes could provide a better understanding of ·OH radical formation pathways in the atmosphere and in consequence, of a more accurate prediction of the oxidative capacity of the atmosphere. Compounds that readily absorb in the tropospheric actinic window (ionic organic complexes, PAHs, aromatic carbonyl compounds) acting as potential photosensitizers of atmospheric relevant processes are explored. The impact of hotosensitation on relevant systems which could act as powerful atmospheric reactors,that is, interface ocean-atmosphere, urban and forest surfaces and indoor air environments is also discussed.

Interaction of protein nutrition and laidlomycin on feedlot growth performance and digestive function in Holstein steers

Two isonitrogenous diets (12.5% CP) containing 20 (20% NPN) or 40% (40% NPN) of the N as nonprotein N were evaluated with 0 or 10 mg laidlomycin propionate (LP)/kg in a 2 x 2 factorial arrangement. Changes in dietary NPN:N ratio were developed by partial substitution of urea N for fish meal N. In Trial 1, four Holstein steers (349 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on digestive function. Total tract OM digestion was slightly greater (1.2%, P < .10) for diets containing 20% of N as NPN, due to greater (3.4%, P < .05) postruminal OM digestion. Supplemental LP decreased passage of microbial N to the small intestine (7.4%, P < .10) and ruminal degradation of dietary CP (DIP, 8.1%, P < .10). Decreasing the NPN:N ratio decreased microbial N flow to the small intestine (7.5%, P < .10) and DIP (15%, P < .01) and increased (6%; P < .05) the flow of indispensable amino acids to the small intestine. Supplemental LP increased (P < .10) ruminal pH. There were no treatment effects (P > .10) on ruminal molar proportions of acetate or propionate. In Trial 2, 120 Holstein steers (122 kg) were used to evaluate treatment effects on growth performance. Decreasing the NPN:N ratio increased ADG (P < .01) by 36, 40, and 16%, respectively, for the initial three 56-d periods of the trial. Overall, ADG was 17% greater (P < .01) for cattle consuming diets containing 20 vs 40% NPN. Decreasing the NPN:N ratio increased (P < .01) gain efficiency by 17 and 14%, respectively, for the initial two 56-d periods. Overall, gain efficiency was 6% greater (P < .01) for diets containing 20% NPN. Dietary NPN:N ratio did not influence (P > .10) the NE value of diets. Supplemental LP did not affect DMI (P > .10) but increased ADG (6%, P < .01) and gain efficiency (5%, P < .05) and decreased (11%, P < .05) the maintenance energy requirements. Protein nutrition limited growth performance of calves receiving the 20% NPN diets during the initial 112 d of the trial. With the 40% NPN diets, protein nutrition limited growth performance throughout most of the trial (d 1 to d 224). We conclude that LP will enhance daily weight gain and gain efficiency of calf-fed Holstein steers. Conventional urea-based diets will not diminish response to LP, although they may not meet the metabolizable amino acid requirements of calf-fed Holsteins during the first three-quarters of the feeding period.

Influence of tempering on the feeding value of rolled corn in finishing diets for feedlot cattle

Crossbred yearling steers (n = 125; 372 kg) were used in a 109-d finishing trial. Steers were fed an 88% concentrate diet containing 65% corn (DM basis) as 1) dry rolled corn (DRC); 2) tempered rolled corn (TRC), 43 mg surfactant (SarTemp)/kg corn; 3) TRC, 172 mg surfactant/kg corn; 4) TRC, 430 mg surfactant/kg corn; and 5) steam-flaked corn (SFC). Corn moisture was greater (3.5%, P < .01) for TRC than for DRC but less (10%, P < .05) than for SFC. Starch enzymatic reactivity was less for TRC than for either DRC (18%, P < .05) or SFC (42%, P < .01). Tempering increased the integrity of rolled corn and reduced the amount of particles less than 2 mm in diameter by 54% (P < .01). Steam flaking corn increased (P < .01) proportion (78%) of the grain having a particle size distribution of greater than 8 mm, as compared with TRC (25%) and DRC (3%). Compared with DRC, tempering enhanced (P < .10) ADG (9%), feed efficiency (5%), and dietary NE (3%). Daily weight gain was similar (P > .10) for TRC and SFC. Feed efficiency (P < .10) and dietary NE (P < .01) were greater (6%) for SFC than for TRC. There were no differences (P > .10) between DRC and TRC in ruminal and total tract digestion of OM, N, and starch, and in ruminal microbial efficiency. Ruminal digestion of OM decreased (linear effect, P < .05) and ruminal microbial efficiency increased (linear effect, P < .05) with increasing surfactant concentration. Ruminal digestion of OM and starch, and flow of nonammonia N to the small intestine were greater (31, 56, and 14%, respectively, P < .01) for SFC than for TRC. Postruminal and total tract digestion of OM, N, and starch, and dietary DE were greater (P < .01) for SFC than for TRC. We concluded that tempering corn will enhance animal performance. Increasing the concentration of surfactant used in tempering may enhance ruminal microbial efficiency and lean tissue growth.

Influence of dietary magnesium level on growth-performance and metabolic responses of Holstein steers to laidlomycin propionate

We used 216 Holstein steers (151 kg) in a 262-d trial to evaluate the influence of dietary magnesium level (.19, .25, and .32%) and laidlomycin propionate (LP; 0 vs 11 ppm, air-dry basis) on growth performance and NE value of the diet. During the initial 112 d of the trial, LP increased (P < .01) ADG (6.3%) and feed efficiency (4.2%). From d 112 until slaughter, LP increased (P < .05) ADG (9.7%) and feed efficiency (4.5%). Across the 262-d feeding period, LP supplementation enhanced (P < .01) ADG (8.9%) and feed efficiency (6.3%). There was an interaction (P < .05) between dietary Mg and LP on NE value of the diet. The enhancement in NE value of the diets owing to LP with .19, .25, and .32% dietary Mg were .5, 3.0, and 5.9%, respectively. Six Holstein steers (302 kg) were used in a 6 x 6 Latin square experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. There were no treatment interactions (P > .10) on site and extent of digestion of OM, starch, and N. Supplemental Mg increased (quadratic effect, P < .10) ruminal OM digestion. Neither LP nor dietary Mg level affected (P > .10) ruminal digestion of starch and feed N. Supplemental LP decreased (15%, P < .05) ruminal microbial efficiency. Total tract digestion of OM and N increased (linear effect, P < .01) with increasing dietary Mg level. There were interactions between LP and dietary Mg level on ruminal soluble-Mg concentration (linear effect, P < .01) and Mg absorption (quadratic effect, P < .05). Apparent total tract Mg digestion increased owing to LP (P < .01) and dietary Mg level (linear effect, P < .01). There were no treatment effects (P > .10) on ruminal pH. Dietary Mg level did not influence (P > .10) ruminal VFA concentrations or molar proportions. Supplemental LP increased (14%; P < .10) total ruminal VFA concentration but did not affect (P > .10) VFA molar proportions. We conclude that LP will increase daily weight gain and feed efficiency of calf-fed Holstein steers and that this response may be enhanced by increasing dietary Mg level.