Air pollution related adverse respiratory health outcomes in California’s San Joaquin Valley: evidence from 2016 linked emergency department and hospital records

The San Joaquin Valley (SJV) of California has been consistently identified as having one of the highest levels of air pollution in the US. Despite federal and state standards, the SJV has been in non-attainment status for daily PM2.5 concentrations, extreme non-attainment for 8 hr O3 levels, and attainment for NO2. An epidemiological time-stratified case-crossover design was used to estimate the relationship between exposure to NO2, O3, PM2.5 and adverse health outcomes in asthma and upper respiratory infections (URIs). This study compared pollutant exposure effects for each case during limited time intervals and adjusted for seasonality. Elevated concentrations of three criteria outdoor air pollutants are associated with increased asthma and URI-related ED visits and hospitalizations in the SJV for all ages. NO2 exposure increased the odds of having an ED visit by 2.4% in lag 1 (95% CI: 1.017, 1.031). Lags 2, 3, 4, 5, 7, 9, and 14 were statistically significant. O3 modestly increased the odds of ED visits by 0.3% (95% CI:1.000, 1.006) after immediate exposure in the warm season. In the cold season, PM2.5 estimates were significant for all lags except for lags 4 and 12. The two-week lag increased the odds by 28% (95% CI:1.218, 1.345) for ED visits, and 16.5% (95% CI:1.009, 1.345) increased the odds of being hospitalized after cumulative exposure to PM2.5. Findings suggest that SJV residents experience adverse health effects due to elevated exposure to NO2 despite attainment of federal and state pollutant standards. This study provides new evidence about the effects of three criteria air pollutants and adverse health outcomes in the SJV region. The air quality regulatory and public health governing bodies should consider revisions to regional pollutant thresholds and local public health strategies to prevent adverse health outcomes during short and prolonged periods of air pollution exposure.


Introduction
Robust scientific evidence suggests that anthropogenic air pollution is a serious public health and environmental concern.Increases in air pollution are associated with polyclinic attendance for asthma, upper respiratory infections (URIs), acute conjunctivitis, bronchitis, emphysema, pneumonia, and lung diseases (Sheldon and Sankaran 2017).Worldwide, the concentrations of two criteria air pollutants, PM 2.5, and ozone, resulted in 7.8 million years of life lost and approximately US$1 trillion in health damages (Anenberg et al 2019, Gao et al 2021).Asthma in children, adults, and the elderly has been clinically defined elsewhere (Chanez et al 2007, Yáñez et al 2014, Castro-Rodriguez et al 2016).The American Thoracic Society recognizes outdoor air pollution as a critical trigger and irritant for asthma exacerbation, shortness of breath, and wheezing (Sockrider and Fussner 2020).Furthermore, in 2019, the U.S. Environmental Protection Agency (EPA) determined that air pollutants (e.g.PM 2.5 , NO 2 , and O 3 ) are likely to cause respiratory effects, such as asthma symptoms and exacerbations (Environmental Protection Agency EPA 2019a).

Pollution control policy standing
The U.S. EPA monitors and regulates over 189 hazardous contaminants, including six criteria pollutants: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, lead, and nitrogen dioxide (EPA 2018).Despite federal and state emission standards, the region has been classified as a non-attainment area since 1997 for fine particulate matter (SJV Air Pollution Control District 2021), which the target set by the state of California is 12 µg m −3 for 24 hr and annual and is more robust than federal air quality goals.In 2019, the EPA announced its decision to reclassify the SJV as an Extreme non-attainment area for 8 hr ozone in the federal register (EPA 2019 b) and has not met the federal and state 8 hr standards of 70 parts-per-billion (ppb) (SJV Air Pollution Control District 2016).As per NO 2 , federal standards consist of 1 hr 100 ppb and annual 53 ppb concentrations, thus the region has achieved attainment status for NO 2 under these thresholds.
Federal and State laws require emission control measures in areas where air pollution exceeds standards or in non-attainment areas (US EPA 2017).The SJV Air Pollution Control District is a public health entity entrusted with the development of local plans and implementation of air pollution control measures.There are plans currently available to target PM 2.5 and ground-level ozone emissions to achieve regional standard goals, but no plans are in place to address adverse outcomes related to SJV residents' exposure to NO 2 .
The SJV Air Pollution Control District is funded by DMV fees, stationary sources and permit fees, and federal/state grants, and is governed by an appointed board made of elected officials and two public members appointed by the Governor (San Joaquin Valley Air Pollution District 2019).Likewise, local county public health departments are commissioned to protect the public's health, prevent illnesses, and respond to endemic factors that complicate the attainment of their constituency's full health.Several local health jurisdictions have found that their communities would like specific diseases, such as asthma and air pollution, need to be addressed in their national public health accreditation action plans (FCDPH 2020, TCHHSA 2017, MCDPH 2023).
This study examined the transient effects of three criteria air pollutants on health endpoints: asthma and URIs.Ground-level ozone and PM 2.5 were interrogated to assess their effects on asthma and upper respiratory morbidity given the region's endemic standing on extreme non-attainment and non-attainment status.NO 2 is included to investigate whether being in emissions attainment status, short-term adverse outcomes are associated with the reported pollutant levels in 2016.The central research question of this study focuses on whether SJV residents exposed to higher concentrations of NO 2 , PM 2.5 , and O 3 have increased odds of visiting the emergency department (ED) and hospitalizations for asthma and upper respiratory complications within 14 d of exposure.

Data and participants
The data for this study were obtained from the California Department of Health Care Access and Information (HCAI), formerly known as OSHPD, non-public ED and hospitalization health care utilization reports for 12 months in 2016.The year 2016 had the lowest reported number of wildfires and forest fires in California ex-ante and ex-post (National Centers for Environmental Information 2017).
SJV residents' visits seen at local hospitals for selected health endpoints: asthma (ICD-10: J45), URIs (ICD-10: J00-J06) and contact with air pollution ICD-10: (Z77.110) were used to select patient records (date of visit/admission, sex, age, race, ethnicity, and zip code).Exposures were assigned using daily values recorded at regulatory monitors located within 15 km of the patient's residential zip code boundary using GIS proximity analysis (ArcGIS ESRI 2023).The methodology to model population-level exposure to air pollution using GIS is widely used in environmental and public health research (Bowen et al 1995, Moore and Carpenter 1999, Maantay 2007, Kanakiya et al 2015).Nevertheless, our study used the proximity tool performing Euclidean analysis to determine distance and proximity to the nearest regulatory station.Based on previous regional studies, an extensive proportion of the SJV region was covered by this methodological grid (Gharibi et al 2018, Entwistle et al 2019).

Cases inclusion and exclusion criteria
For both ED visits and exclusion criteria for inclusion and hospitalizations were as follows: The inclusion criteria were as follows: (1) Having an HCAI unique identifier assigned, known as the record linkage number (RLN); (2) patients older than 2 years of age; and (3) cases with selected health endpoint ICD-10 codes as the principal diagnosis.
The exclusion criteria were as follows: (1) duplicate cases identified through the RLN, (2) cases without an RLN, (3) patients younger than 2 years of age, and (4) cases without a selected health endpoint as the principal diagnosis.

Study design
This epidemiological study used a time-stratified case-crossover design that is appropriate for analyzing the associations between exposure and adverse health outcomes (Maclure 1991, Malig et al 2016).This strategy minimizes endogeneity, as each case serves as its own control when comparing the exogenous exposure variables during the day of the health event to three or four similar periods calculated on the same days of each week during the same month of the hazard period (e.g. the reported date of admission/visit).
To replicate the prevalent pollution conditions in the SJV, single day lags up to 14 d prior to the event day were estimated for each pollutant, and cumulative lags were calculated to investigate the acute role of PM 2.5 , O 3 and NO 2 in asthma hospital admissions and emergency room visits.

Exposure assessment
The source of air pollutant (O 3 , NO 2 , PM 2.5 ) data was retrieved from the U.S. EPA National Ambient Air Quality Standards system, 40 CFR part 50, and is publicly available.This study utilized pollutant concentrations and meteorological data from 18 sampling regulatory stations in the region to create exogenous variables of exposure for each pollutant and meteorological indicator.There was no geographical overlap between any regulatory stations.The measurements for NO 2 and PM 2.5 are the daily average values, and the measure for ground-level ozone was the daily 8 hr average.The meteorological variable temperature was computed as the mean daily degree Celsius ( • C).

Statistical analysis
Conditional logistic regression was used to estimate the association between O 3 , NO 2 and PM 2.5 and asthma and URI-related visits to the ED and hospitalizations.Because this study aimed to estimate the transient acute effects of three criteria air pollutants on attendance to emergency rooms and hospitalizations in 2016, it was appropriate to employ a time-stratified case-crossover analysis.Lags up to the 14th day were estimated to capture the acute health effects and presentation to the ED and hospitalizations after exposures above the averages.
All exposure models were adjusted for meteorological conditions in temperature using the restricted cubic spline (RCS) method with three degrees of freedom (3 df).
Its function was based on prior studies (Gharibi et al 2018, Entwistle et al 2019, Cisneros et al 2021): Y k is daily counts of asthma and URI events on kth day.
, and )) stand for the case covariates, that is, the control day or the day that a patient attended the ED or was hospitalized. ( , and )) are covariates for up to four matched controls within the same month.
l is the number of days before the event day (l = 1-14 d before the event day).Furthermore, match control days are shifted subsequently by l day ((k − l) j).β = β1, β2, β3 refer to the coefficients of each covariate.Finally, β * denotes the paired coefficients of the meteorological variables included in the RCS.Note that the RCS with k-knots was equal to three in this study.Seasonality is a major factor in the presence and effects of each of the pollutants included in this study, specifically for ozone in the prolonged regional summer months and the winter season for PM 2.5 .Therefore, the analyses were stratified by regional warm (June, July, August, and September) and cold (November, December, January, and February) seasons to measure the temporal effects.During the cold season, PM 2.5 is sequestered by temperature inversion layers that may impact concentration variability.
In the sensitivity analysis, humidity and wind were found to have moderating effects, causing asymptotic errors, and were removed from the spline.
To avoid case duplication, each data set for ED visits and hospitalizations was analyzed individually.The cases included in this case-crossover sample were evaluated for associations between socio-demographic characteristics of SJV residents who were patients in the ED or hospitalized in 2016 for asthma or URI events.A categorical variable was created from the continuous values of each pollutant concentration at the lowest and highest percentiles.
This study received IRB approval by the State of California Health and Human Services Agency Committee for the Protection of Human Subjects #2021-051.All analyses were conducted using Stata V17 software (College Station, TX, USA).

Demographics of ED and hospital data in 2016
Table 1 presents the patient characteristics of asthma and URI visits to the emergency room and hospital admissions of SJV residents.This study included 34 591 ED visits and 4693 hospitalizations during the 12 months of 2016.For both ED visits and hospitalizations, there were more females (56.4% and 51.4%, respectively) than males (43.5%-48.6%).The proportion of patients by race and ethnicity for ED visits and hospitalizations showed that most patients who visited the emergency rooms in SJV were Hispanic (46.2%), and for hospitalizations, half of all patients were Caucasian/White (50.1%).African Americans accounted for approximately 13% of patient ED visits and hospitalizations, and Asian Americans had a higher proportion of hospitalizations (9.2%) and 5.4% of 2016 emergency room visits for asthma and URIs.The mean age for patients who went to the ED for asthma and URI events was 36.06 years old (±23.87),and for those admitted to the hospital, the mean age was 60.63 years old (±22.28).The analysis by age group shows the highest proportion of ED visits was for patients aged 19-40 years (31.5%), and for hospitalizations, those who were 65 years and older accounted for almost half (49.2%) of all hospital admissions.Lastly, Medi-Cal accounted for 58.9% of all ED visits by payer source, and Medicare was the insurer for 54.9% of hospital admissions due to asthma and URIs.For the latter, the average length of stay per inpatient care episode was 6.3 d, and the median was 3 d.

Descriptive analysis of criteria air pollutants and meteorological factors
Table 2 describes the daily 8 hr concentration of O 3 , the daily mean concentrations of PM 2.5 , NO 2 , and the temperature from sampling stations in the SJV during 2016.After adjusting for seasonality, mean concentrations for the cold and warm seasons were included based on temporal pollutants and primary/secondary behavior.The temporal relationship for each pollutant concentration was investigated,   Table 3 reports the characteristics of emergency room and hospitalization patients who were exposed to the 75th percentile to the maximum level registered by sample monitoring stations in 2016, and the estimated p-value.The likelihood-ratio test was used to estimate the associations between exposure to ambient air pollution and SJV patients' county of residence, sex, race and ethnicity, age group, and payer source for the visit and hospitalization.
The patient's county of residence, race, ethnicity, and age group were likely to be associated with exposure to the highest level of every pollutant registered in 2016 included in the study.The probability of sex association was only statistically significant, with the highest exposure to ozone percentiles for hospitalized patients and for ED patients for exposure to high levels of nitrogen dioxide.In addition, for hospitalized patients, the association between high exposure to all three pollutants was likely significant.For patients who visited the ED, only the relationship with high exposure to PM 2.5 was found to be significant.In this study, the payer source is utilized as a potential proxy for income levels and access to care in the SJV, which could explain why the largest percentage of patients in the sample were self-pay at the time of visit or admission.

Unadjusted and adjusted pollutant models for ground-level Ozone
Table 4 shows the association of ozone with ED visits and hospitalizations of SJV residents during the warm season months.The unadjusted single pollutant model estimated a 0.3% (95% CI:1.000, 1.006) increase in the odds of visiting the ED for asthma at lag 0. No other lags were statistically significant.In the model for hospitalization, lag 0 had 0.5% increased odds of being admitted for asthma; however, the estimate was not statistically significant.
Table 5 shows the associations between asthma ED visits and hospitalization using ozone models adjusted for temperature.The second model was adjusted concomitantly in a multi-pollutant scenario with temperature and NO 2 .None of the estimates for admission or emergency room visits were statistically significant during the warm season.

Unadjusted and adjusted pollutant models for NO 2 (warm season)
Further unadjusted estimates, shown in table 6, of the associations between air pollution and asthma, found that NO 2 was associated with ED visits and hospital admissions during the warm season.For ED visits lags 0-5, 7, and 14 were statistically significant, with the highest increased odds of having an ED visit for an asthma event at lag 0 of 3.1% (95% CI:1.026,1.037) to 1.2% (95% CI:1.005-1.020) in lag 7. The acute effects of NO 2 for cumulative lag 0-7 were 12.8% (95% CI:1.029, 1.238) and 24.7% (95% CI:1.116, 1.393) at lag 0-14 to attend the emergency room for asthma and URIs, respectively.The model for hospitalizations associated with NO 2 showed that lags 0, 1, and 7 were statistically significant; thus, the odds of being hospitalized during the warm season for asthma due to air pollution were 3.6% (95% CI:1.017, 1.048) on lag 0 and 2.6% (95% CI:1.007, 1.046) on lag 7. A cumulative lag of 0-7 for NO 2 exposure was associated with a 37.7% (95% CI:1.082, 1.753) increase in the odds of being hospitalized for asthma in the warm season.Adjusted models for NO 2 associations with asthma and URIs, ED visits, and hospitalizations included temperature, and a multi-pollutant model adjusted for temperature, ozone, and PM 2.5 ; see table 6.When controlling for temperature, in lag 0, SJV residents had 2.1% (95% CI:1.015, 1.027) increased odds of visiting the ED.In the multi-pollutant model and controlling for temperature, during the warm season, increases in NO 2 exposure increased the odds of having an ED visit, ranging from 1.3% (95% CI:1.006, 1.020) in lag 5%-2.4% (95% CI:1.017, 1.031) in lag 1. Lags 2, 3, 4, 5, 7, 9, and 14 were statistically significant for the increased odds estimates of having an ED visit due to NO 2 pollution.The cumulative lag 0-14 provided an estimate of 27.4% (95% CI:1.140, 1.424) increased odds of visiting the ED for asthma exacerbation or a URI.The adjusted single-and multi-pollutant models for hospitalization are also included in table 7. When controlling for temperature, at lag 0, exposure to NO 2 was associated with 2.3% (95% CI:1.006, 1.040) higher odds of being hospitalized due to an asthma or URI event during the warm season.Including ozone and PM 2.5 modifies the significance of lags 1 (95% CI:1.007, 1.045) and 7 (95% CI:1.007, 1.046) to 2.6% higher odds, as well as cumulative lag 0-7 (95% CI:1.073, 1.737) to 36.5% higher odds of being hospitalized for asthma or URI events.Lag 0 increased in magnitude by 2.8% (95% CI:1.008-1.048)higher odds.

Unadjusted and adjusted pollutant models for PM2.5 (cold season)
The unadjusted estimates for ED visits associated with PM 2.5 , shown in table 8, were significant for all lags except lag 4, ranging from 0.05% (95% CI:1.001, 1.009) to 1.7% (95% CI:1.013, 1.020) increased odds.The cumulative lag 0-14 was associated with 28.1% (95% CI:1.219, 1.346) increased odds of having a visit to the ED during the cold season.For hospitalization, the unadjusted estimate for lag 0 was associated with 1.9% (95% CI:1.010, 1.029) increased odds of having been admitted to the hospital due to asthma exacerbation or a URI.The cumulative exposure lag 0-14 was found to be associated with 17.3% (95% CI:1.016, 1.353) increased odds of hospitalization.
Table 9 shows the adjusted models for ED visits and hospitalizations when controlling for temperature during the cold season and concomitant NO 2 .The estimates of the association between exposure to PM 2.5 and asthma, and URI health endpoints continued to be significant for all lags except for lags 4 and 12.The cumulative lag 0-14 found a similar association as the single pollutant unadjusted model in which SJV residents had 28.0% increase in the odds of attending the emergency room due to asthma or URIs.For hospitalizations, lag 0 while controlling for temperature and NO 2 showed a significant 1.5% (95% CI:1.004, 1.026) increased odds of hospitalization.The cumulative lag 0-14 shows an association of 16.5% (95% CI:1.009, 1.345) with increased odds of hospitalization after cumulative exposure to PM 2.5 .

Discussion
This study identified the increased odds of ED visits and hospitalization for asthma exacerbations and URIs resulting from exposure to higher concentrations of three criteria pollutants: PM 2.5 , O 3 , and NO 2 .The results confirmed that SJV residents were increasingly vulnerable to short-term increases in outdoor pollution, asthma, and URIs.The study also reports the patient characteristics of SJV residents who were exposed to higher pollution, in which relative differences between counties, age groups, and race/ethnicity are likely to be significant.Sex was not significant; however, the payer source yielded mixed estimations.The payment source was utilized as a proxy for the income level of patients and illustrated that emergency rooms and hospitals may be the only source of care for uninsured SJV residents when asthma and respiratory health are exacerbated by pollution exposure.Inquiring about the effect modification in the association between exposure to ambient pollution and asthma by socioeconomic variables and its mechanisms was not part of this study but could be worth investigating in future work.
For the year 2016, the cases included in this time-stratified case-crossover study found an unadjusted association between higher levels of exposure to ground-level ozone during lag 0 in the warm season, with 0.3% increased odds of visiting the ED for asthma or URI events and not for hospitalizations.In their single pollutant model, Gharibi et al (2018) found 2.7% increased odds of an asthma ED visit on lag 1 during the warm season in the SJV region for years 2005-2015, whereas Entwistle et al (2019) found 4.2% increase in the odds of an ED visit for asthma for a 5 ppb increase in the daily mean maximum exposure to ground-level ozone.The adjusted and multi-pollutant O 3 models did not estimate the associations between higher exposure and attendance to the ED or hospital admissions.This study findings for O 3 in a multi-pollutant model differ from those of previous studies conducted in the region, but those analyses included 11 year  pooled data (Gharibi et al 2018, Entwistle et al 2019), and this study included reported ED and hospital data for a single year.Because this analysis did not investigate variations in O 3 distribution in rural and urban areas, and because of the lack of pollutant data from important rural population centers in the region, the ozone paradox was not investigated (Cisneros andPerez 2007, Malashock et al 2022); alas it could have contributed to the modest health outcome effects.However, similar exposure studies conducted in Northern California, France, and a meta-analysis did not find a conclusive association between asthma and exposure to ozone (Laurent et al 2008, Anderson et al 2013, Chang et al 2016).
In federal standard attainment status, NO 2 emerged as the cause of the increase in asthma ED visits and hospitalizations during the warm season for SJV residents exposed to marginal elevations in pollutant concentrations.The ozone and NO 2 concentration distributions in the region were inversely related to their chemical reactions, as nitrogen dioxide is a precursor of ozone formation.These findings are consistent with existing studies (Brandt et al 2014, Tavallali et al 2020, Cisneros et al 2021).
Thus, during the 2016 warm season, NO 2 estimates indicated that increases in exposure increased the odds of hospitalization and ED visits for asthma and URIs in the single-, adjusted-, and multi-pollutant models.The estimates increased in magnitude when the model was adjusted for PM 2.5 and O 3 and controlled for temperature, which may be indicative of the synergistic effect of NO 2 and concomitant pollutants on human health.While studying the cumulative effects of NO 2 , the multi-day lag of the preceding two-week exposure indicated 27.4% increased odds of having an emergency visit for asthma and URIs.Relatedly, Cisneros et al (2021) found 29.6% increased odds of an asthma ED visit associated to two-week exposure to NO 2 for SJV residents and other regions of California using data from 2005-2015.
Although PM 2.5 has been associated with mortality [and higher monetization], its transient effects on SJV cases of nonfatal asthma and URI-related morbidity were studied.Modeling included adjusting for the cold season to address the nonlinearity of pollutant and meteorological factors.Other studies have included temporal interactions in their exposure modeling to determine if regional seasons are mediators of health outcome associations, and several studies have found a relationship between asthma and the impact of PM 2.5 as an irritant (Gleason et al 2014, Fan et al 2016).
The single pollutant model for PM 2.5 indicates that during the cold season in the SJV, every single day exposure to PM 2.5 is significantly associated with increases in the odds of ED visits, except for lag 4. The cumulative effects of 14 days of precedent exposure resulted in a 28% increase in the odds of visiting the ED for asthma exacerbation.Single-day estimates of PM 2.5 exposure (lag 0, 13, and 14) showed increased odds of hospitalization due to asthma and URIs, and cumulative exposure (lag 0-14) increased the odds of hospitalization for asthma by 17.3%.The adjusted model, controlled for NO 2 and temperature, had a similar magnitude of effect for single-and multi-day exposure to PM 2.5 .Short-term exposure to ambient particulate matter has been linked to children and adult hospitalizations for respiratory diseases, and the findings of this study are consistent with the existing literature (Li et al 2018, Tian et al 2019, Wang et al 2021).Because PM 2.5 may be emitted as a primary pollutant through the combustion of fossil fuels, and as a secondary pollutant through the chemical interactions with other pollutants, it is clear that microscopic particulate matter is deterministic for adverse respiratory health outcomes.Furthermore, due to the unique geography of the SJV, during the cold season, PM 2.5 is sequestered by temperature inversion layers, resulting in concentration and distribution spikes.

Limitations
Because pollutant data within a 15 km radius from any sample station were not available from important population centers in the SJV, such as Los Banos City and the town of Oakhurst in the hills of Madera County, the odds of attending the ED or being hospitalized due to asthma and URIs could have been underestimated.The lack of pollutant data for some rural areas allowed for the exclusion of ED visits and hospitalizations due to the respiratory effects of their residents.Despite the importance of these communities in the region, federal pollution monitoring is absent.
Misclassification could have occurred because the levels of ambient pollution were used to ascertain the personal exposure of the residents.Air pollution exposures were assigned to each of the patient's residential zip codes 15 km from the sampling station, which could have caused weak correlations between pollutant concentrations and the health endpoints included in the study.
Another limitation is the potential for case exclusion because only principal diagnosis codes were used, and selected health endpoints reported as secondary, or tertiary were not included in the analysis.This may have resulted in a lack of specificity, but there was a tradeoff in the selection of inclusion/exclusion criteria to avoid non-ambient air pollution-related outcomes.

Conclusion
This study adds to the limited available knowledge on monitoring and surveilling adverse health outcomes and morbidity associated with air pollution for the SJV.This evidence is particularly important because SJV is a region disproportionally affected by poor air quality, and more recently forest fires and wildfires have further challenged the state of public health.
Compared to 2015, California experienced considerably fewer wildfires in 2016 than the previous record-setting year (NCEI 2017).This fact could have affected this study's ozone exposure association estimates, which had modest effects on asthma and URIs ED visits and no association with hospitalizations.This includes the unavailability of pollutant data from notable rural population centers in the region resulting in the exclusion of residents' ED visits, and hospitalizations.
Despite being within federal standards attainment status, exposure to single-and multi-day exposure to NO 2 was associated with increased odds of ED visits for asthma, URIs, and hospitalizations.This suggests that nitrogen dioxide is the cause of most ED visits and hospitalizations for asthma exacerbations during the warm season in SJV at levels considered 'Good' in the established air quality standard.
Further research is needed to estimate the tangible and intangible costs of air pollution to the residents of the region to support the inclusion of non-fatal health endpoints in decision-making and to evaluate what mitigation and control efforts are more likely to be supported by SJV residents.This has critical implications for public health agencies, whose pivotal role is to prevent illness and disease using an equity framework, and for regulators who develop and revise standards using evidence of pollutant effects on health outcomes.

O3Figure 1 .
Figure 1.Temporal distribution of pollutant concentrations for the SJV region in 2016.

Table 1 .
Characteristics of ED and hospitalizations for Asthma/URIs.

Table 2 .
Distribution of air pollutants in the SJV from sampling stations.

Table 3 .
Patient characteristics for exposure to highest pollutant concentration percentiles.